Synthesis of Scientific Knowledge and Uncertainty about Population Dynamics and Diet Preferences of Harbour Seals, Steller Sea Lions and California Sea Lions, and their Impacts on Salmon in the Salish Sea

Technical Workshop Proceedings May 29-30, 2019

Editors: Andrew W. Trites David A.S. Rosen

Hosted by:

Marine Mammal Research Unit Institute for the Oceans and Fisheries University of British Columbia Vancouver, BC, Canada

Synthesis of Scientific Knowledge and Uncertainty about Population Dynamics and Diet Preferences of Harbour Seals, Steller Sea Lions and California Sea Lions, and their Impacts on Salmon in the Salish Sea Technical Workshop Proceedings May 29-30, 2019 UBC Marine Mammal Research Unit

Editors: Andrew W. Trites David A.S. Rosen

These workshop proceedings should be cited as:

Trites, AW and Rosen, DAS (eds). 2019. Synthesis of Scientific Knowledge and Uncertainty about Population Dynamics and Diet Preferences of Harbour Seals, Steller Sea Lions and California Sea Lions, and their Impacts on Salmon in the Salish Sea. Technical Workshop Proceedings. May 29-30, 2019. Marine Mammal Research Unit, University of British Columbia, Vancouver, B.C., 67 pages.

The information contained in this document is provided as a public service. Although we endeavor to ensure that the information is as accurate as possible, errors do occur. Therefore, we cannot guarantee the accuracy of the information. It is important to note that the opinions and suggestions contained in this document do not necessarily reflect a consensus of every workshop participant, nor the institutions or organizations they represent.

Cover image credit: Harbour seal, photograph by Andrew Trites

Marine Mammal Research Unit Institute for the Oceans and Fisheries University of British Columbia Room 247, AERL, 2202 Main Mall Vancouver, B.C. Canada V6T 1Z4

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Table of Contents Workshop Summary ...... 6 Workshop Structure ...... 8 Goals...... 8 Scope ...... 8 Participants...... 8 Agenda...... 8 Knowledge Gaps and Research Priorities...... 8 Group Reflections on State of Knowledge ...... 9 How good are the pinniped abundance data? ...... 9 Are better diet estimates needed to make management decisions? ...... 10 What additional data are required to resolve the impact of pinnipeds on salmonids? ...... 11 What else needs to be factored into a full assessment of predatory impacts of pinnipeds? ...... 12 Other fish...... 12 Stock-specific analyses...... 12 Other predators...... 13 Role of hatcheries...... 13 Man-made objects...... 13 Reconciling contrary trends...... 13 How can estimates of consumption and predation rates be improved? ...... 14 Improving predation estimates...... 14 Improving consumption estimates...... 14 Would removing pinnipeds increase juvenile salmon survival? ...... 15 Other mechanisms that affect predation...... 15 Compensatory mortality – is it a major factor? ...... 15 Next Steps—Resolving Uncertainty ...... 16 1. What are the biggest knowledge gaps that need to be filled to draw sounder conclusions about the role of pinnipeds in the ecosystem? ...... 16 Broader ecosystem considerations ...... 16 Pinniped numbers and diet ...... 17 Fish dynamics ...... 18

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2. How can the impact of predation by seals on salmon be assessed without doing an experiment? .. 19 3. What experiment could be done and what is the time frame to assess the outcome?...... 19 Vary hatchery production ...... 20 Enhance fish survival ...... 20 Non-lethal removal of pinnipeds ...... 20 Lethal removal of pinnipeds ...... 21 4. What are the research priorities going forward? ...... 21 Pinniped abundance ...... 21 Pinniped diet ...... 21 Impact of predation on salmon ...... 21 Conclusions ...... 23 What Actions to Take ...... 23 Future Refinement and Planning ...... 23 Acknowledgements ...... 23 Appendix A: Participants ...... 24 Appendix B: Agenda ...... 26 Appendix C: Summary of State of Knowledge and Uncertainties ...... 31 Pinniped abundance & trends ...... 31 Pinniped diets & trends ...... 32 Prey abundance & trends ...... 33 Pinniped foraging behaviour ...... 35 Perspectives on pinniped impacts on prey species ...... 36 Rates of predation on salmonids and amounts consumed by pinnipeds ...... 36 Cowichan focal area—rates of predation ...... 38 Factors that affect pinniped predation of salmonids ...... 39 Ecosystem considerations ...... 39 Appendix D: Participant Presentation Summaries ...... 41 Day 1 – Pinniped Abundance, Distribution, Sex and Age Composition, and Seasonal Movements ...... 41 Day 1 – Pinniped Diets and Diet Trends: Seasonal and Inter-Annual Year Variability; Sex-Based Variability; Specialization ...... 43 Day 1 – Pinniped Prey Abundance, Trends and Availability to Pinnipeds in Salish Sea ...... 47

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Day 1 – Pinniped Foraging Behavioural Diversity, Size Selectivity, and Spatial and Temporal Differences in Predation Pressure on Salmonids ...... 54 Day 1 – Perspectives on Pinniped Impacts on Commercially and Culturally Important Prey Species in Eastern Canada ...... 56 Day 2 – Rates of Predation on Salmon and Steelhead and Amounts Consumed by Pinnipeds in Salish Sea and Coast ...... 57 Day 2 – Rates of Predation And Amounts Consumed – Cowichan Focal Area...... 61 Day 2 –Factors that Affect Pinniped Predation of Salmonids ...... 63 Day 2 – Ecosystem Considerations: Indirect Effects of Pinniped Predation on Salmon Mortality, Effects of Disease on Predation Rates, and Questions Surrounding Additive and Compensatory Mortality .... 64

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Workshop Summary 3) What additional data are required to resolve the impact of pinnipeds on salmonids? This workshop assembled scientists and 4) What else needs to be factored into a full managers with technical expertise on seals, sea assessment of predatory impacts of lions, and salmonids to identify and evaluate pinnipeds? knowledge and uncertainties about the diets and 5) How can estimates of consumption and population dynamics of pinnipeds (harbour predation rates be improved? seals, Steller sea lions, and California sea lions), After hearing all of the presentations, the as well as the impacts that pinnipeds may be workshop groups addressed four pre-defined having on salmonids in British Columbia and questions related to resolving uncertainties Washington State waters. The primary focal area about pinniped impacts: was the Salish Sea, but included coastal Washington and British Columbia. Pinniped 1) What are the biggest knowledge gaps that impacts in the Columbia River basin were not need to be filled to draw sounder conclusions addressed. about the role of pinnipeds in the ecosystem? 2) How can the impacts of predation by seals on The workshop focused on what is known about salmon be assessed without doing an predation by seals and sea lions on salmon—and experiment? how assumptions and uncertainties in the data 3) What experiment could be done and what is affect the conclusions drawn to date about the the time frame to assess the outcome? effect of pinnipeds on salmon. 4) What are the research priorities going Workshop participants listened to presentations forward? on the state of scientific knowledge about 1) It was readily apparent over the course of the pinniped abundance, diets, and feeding workshop that considerable research has behaviours, 2) prey abundance, and 3) rates of occurred over the past decade in the Salish Sea predation on salmon by pinnipeds in the Salish to evaluate the role that pinnipeds may be Sea and within a long-term Salish Sea study site playing in the dynamics of salmonid populations. (Cowichan Bay). They also considered 4) the It has resulted in significant advances in factors that affect rates of predation by identifying the proportion of salmon in pinniped pinnipeds on salmon (e.g., density of other prey diets, including the species consumed by males species, hatchery practices, other predators of and females by time of year, location, and life salmon, presence of transient killer whales, and stage. Research has also contributed to man-made objects and conditions) as well as 5) understanding when and how predation is ecosystem considerations (e.g., additional direct occurring, and the environmental factors that and indirect effects of predation by seals). affect predation rates. Other research has added Following sets of presentations on particular significant insights into the possible direct and themes, workshop participants split into four indirect effects of predation by pinnipeds on groups with an even distribution of expertise. salmon and the Salish Sea ecosystem. They were tasked with discussing: However, this increase in knowledge has also 1) How good are the pinniped abundance data? come with a greater appreciation of the 2) Are better diet estimates needed to make uncertainties, biases and limitations inherent in management decisions? some of the data sets that constrains applying them to draw definitive region-wide conclusions

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about how pinnipeds affect the Salish Sea of animals using the haulouts were also ecosystem. Workshop participants repeatedly identified as research priorities. noted that additional data are needed on The potential impact of pinnipeds on salmon aspects of pinniped foraging. However, they depends on the proportions of seals and sea were equally adamant that additional data are lions that are salmon specialists, which likely also needed on salmon, because ascertaining the vary by region and salmon life-histories. Greater impacts of predation is as much a salmon attention should also be given to sea lion question as it is a pinniped question. predation on adult salmon (as compared to the It was further noted that the system is current primary focus on predation by seals on exceedingly complicated, and that this juvenile salmon). Finally, consideration needs to complexity must be more clearly understood to be given to the alternative hypothesis that make accurate predictions. Ecosystem models bottom-up effects of food supply and food-web are one means for gaining better insights, but competition are primarily responsible for poor they currently lack the necessary data to juvenile survival which inhibits recovery of accurately model the system and therefore salmon. predict the outcome of potential management This workshop was a first step in bringing actions. Many of the data gaps identified by together scientists and managers with pinniped workshop participants relate to uncertainties in and salmon expertise from Canada and the pinniped numbers, diets, and salmon United States to identify and evaluate the impact demographics. that pinnipeds may be having on salmonids. It Reducing uncertainty in estimated numbers of has identified the major knowledge gaps and pinnipeds in the Salish Sea requires better need for focused research to address the key census data. This can be improved by having uncertainties that prevent drawing definitive greater transboundary coordination for aerial conclusions about the role that pinnipeds play in counts, increasing US survey efforts, and the Salish Sea and their impact on other counting seals and sea lions in rivers. Count important ecosystem components such as correction factors used to account for animals salmon. not seen on land during surveys also need to be updated to get more precise abundance estimates by regions and pinniped age-classes. Better pinniped diet data is required to address current uncertainties, including potential biases. Data are needed on species and size-class composition of diets, consumption rates, and other prey populations (such as herring and hake that dominate their diets). It is particularly important to obtain stock-specific salmon diet data to ascertain which salmonid populations are being consumed given divergence in stock- specific survival trends of indicator stocks. Addressing biases in diet description associated with basic methodology, geographic biases, small sample sizes of scats, and the sex and age

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Workshop Structure 3. What additional data are required to resolve the impact of pinnipeds on Goals. To engage scientists and managers with salmonids? technical expertise relevant to: 4. What else needs to be factored into a full A. Providing knowledge about pinniped assessment of predatory impacts of population dynamics and diet preference, pinnipeds? B. Understanding existing scientific know- 5. How can estimates of consumption and ledge about pinniped predation, and predation rates be improved? C. Identifying knowledge gaps and next steps. The final session of the workshop was dedicated Scope. Discussions and presentations focused on to having the four groups address specific the Salish Sea, but included coastal information questions related to knowledge gaps and where relevant. Information sought included research priorities. population dynamics of pinnipeds (harbour Participants discussed the following four seals, California sea lions and Steller sea lions), questions: temporal and spatial trends in diets, characteristics of populations that influence diet 1. What are the biggest knowledge gaps that preference, combined impacts of multiple need to be filled to draw sounder predator species on salmon, and ecosystem conclusions about the role of pinnipeds in considerations (e.g., effects of pinniped the ecosystem? consumption on dynamics of other species). 2. How can the impacts of predation by seals on salmon be assessed without doing an Participants. Participants with technical know- experiment? ledge about pinnipeds, salmon, and fisheries 3. What experiment could be done and what management were invited from Canada and the is the time frame to assess the outcome? United States. These included 39 individuals 4. What are the research priorities going working for state and federal governments, forward? consulting companies, tribes, nonprofit These questions were discussed by the four organizations, and universities (Appendix A). groups to generate independent lines of Focus was on technical expertise rather than thought, and then presented to the entire representation from specific groups. workshop for consideration. The points raised Agenda. The workshop alternated between did not necessarily reflect consensus among all presentations by scientists on their fields of participants, but rather reflected the diversity of expertise, and group discussions and review of opinions. the information presented (Appendix B).

Knowledge Gaps and Research Priorities. Following the end of the scientific presentations

(Appendices C & D), participants were split into four groups with an even distribution of expertise to discuss: 1. How good are the pinniped abundance data? 2. Are better diet estimates needed to make management decision?

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Group Reflections on State of difficulties in relating new estimates to previous results. Knowledge Most survey methods use a correction factor to Following the end of the scientific presentations account for animals that are not visible on land on the state of knowledge (see summaries in when surveys are flown. In some ways, Appendices C & D), four groups of workshop participants with an even distribution of inaccurate correction factors may be more of a expertise discussed five questions related to concern than inaccuracies in counts. Small errors uncertainties, data needs, and ways in which in correction factors can dramatically increase or assessments of consumption and predation decrease estimates of abundance and impacts can be improved. The following consumption since correction factors are a direct amalgamates the central points made during multiplier used to estimate the proportion of group discussions. animals not seen during a survey. Therefore, it is important to account for uncertainty associated How good are the pinniped abundance data? with the correction factor used to derive total Concern was expressed about the frequency and population sizes. consistency of pinniped population surveys in The commonly used Huber et al. correction Canada and the United States. Seals and sea lions factors are 30 years old. They need to be are mobile, and frequently cross the updated using current data on haulout patterns. international boundary in the Salish Sea. There is reason to believe that correction factors Consequently, greater coordination between are not necessarily static, and that they likely managing entities (timing, methods, and quality differ by region. Factors that might influence control) can improve overall estimates of correction factors include changes in predation numbers and their distributions. pressure on seals (caused by transient killer Greater survey frequency will increase the ability whales and terrestrial predators such as wolves to recognize real annual trends (vs. error due to and cougars), exposure and habituation to sampling and process variation) as well as humans (level and type of activity), and physical seasonal fluctuations (important for prey environment (type of haul out and surrounding impacts). However, this may not be feasible over water). Research is being undertaken and may the entire range. Using index sites can help to be expanded to produce suitable species- reduce the costs of increased survey frequency, appropriate correction factors. and would be most appropriate for “stable” For harbour seals, there is concern about populations (in numbers and location; e.g., potential expansion in numbers outside of the harbour seals in the Strait of Georgia). Strait of Georgia. Coast wide surveys were Unfortunately, it is less useful for California and completed in British Columbia in 2018, but will Steller sea lions whose populations are more take a couple of years to yield final estimates. dynamic. Sea lion surveys need to increase in frequency. New methods (e.g., satellite imagery, genetic The range of California sea lions appears to be analysis) might provide better total estimates rapidly changing (perhaps in an unpredictable and more relevant population details (e.g., age fashion), which could have large ecological and sex distribution). However, there may be impacts that change annually. Surveys of Steller sea lions may be more important to address

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 9 because their consumption impact on Sea can vary significantly from year to year, and commercial species may be greater than does not necessarily follow the smoother previously recognized. Riverine surveys also population trends of the total California sea lion need to be undertaken, given the potential population breeding in Mexico and California. concentration of predation impact on salmon. The distribution and abundance of males during the non-breeding season is likely to vary It is often assumed that the level of predation depending on where food resources are pressure depends on the size of the predator abundant. Additional increases in numbers could population. However, there are questions also occur in the Salish Sea if climate change regarding the applicability of applying overall expands the northward distribution of California population sizes of predators to estimate the sea lions. effects of local predation. For example, there The Eastern population of Steller sea lions is may be almost no relationship between total increasing range-wide, but it is unknown seal abundance and salmon abundance whether the Steller sea lions seen in the Salish (although there may be relationships at a Sea reflect the overall increase in abundance or localized level). is due to a change in their distribution. New Changes in population growth rates are rookeries (breeding sites) are being established constrained by the ability of the ecosystem to in BC and WA. It is unknown whether their support the population (i.e., carrying capacity). growth will ultimately be limited by food or by However, carrying capacity is not fixed for any predation. marine mammal population. Understanding what factors limit population size is incomplete Are better diet estimates needed to make management decisions? (i.e., food, predation, haulout space). The consistent survey data from Canada and the Answering this question hinges on how much the less consistent data (in recent years) from reconstructions of pinniped diets are biased due Washington State suggest that harbour seal to methodologies, sampling regimes, etc. — and populations are relatively stable or declining how these biases impact predation estimates. slightly within inside waters (Strait of Georgia Biases in diet estimates may also have been and Puget Sound) indicating they are at or near introduced by the combination of genetic and carrying capacity. However, it is uncertain if this traditional methodologies now being used. is also the case along the outer coast. Timing of There was strong consensus that the different the leveling off trend were similar in OR, WA, and methodologies used to describe diets need to be BC. However, the carrying capacity could be validated using controlled feeding trials with going down with increased predation pressure captive animals, particularly Steller sea lions. and decreased fish abundance. In coastal This should be a high research priority. Washington, there is some suggestion of a declining harbour seal population. There was also concern that a significant bias associated with the sex of the pinnipeds using California sea lions appear to be at carrying haulouts where scats are collected has been capacity. The small breeding sites in Mexico are introduced into some diet estimates. A number declining, while the much larger colonies in (but not all) of the sampling sites have significant California appear stable (although numbers of biases in male vs female scat samples. It is pups born each year has decreased). The unknown whether it is a population bias, a real presence of male California sea lions in the Salish

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 10 sampling bias, or apparent bias due to times (e.g., Johnstone Strait in late summer methodology. when Fraser River bound sockeye pass through).

Resolving the question of sex-bias might be done It is also important to differentiate between by looking at other types of data (e.g., live- estuary and non-estuary data (an example of capture data) relative to fecal samples to see data stratification), recognizing that it is harder whether there is sex-based sampling bias. The to get scats in non-estuary sites. This opinion was problem might also be minimized by using the not universal; others suggest collecting as gender-based data to construct a sex-specific broadly as possible and see what patterns consumption estimate vs complete population emerge, and not to be as concerned by such estimate (assuming that the bias is due to differences as estuary and non-estuary sampling and not analysis). representation. Regardless of the approach, sampling designs should take into consideration Diets are unlikely to be uniform across the relatively high site fidelity of harbour seals individuals or within a species, time, or but very large migratory patterns of California geographic area. This reflects the inherent and Steller sea lions. variability in pinniped diets. For example, the diets of seals using six different haulout sites What additional data are required to resolve within Puget Sound have been found to have the impact of pinnipeds on salmonids? very different diet profiles. However, diet The nature of the question “What do pinnipeds variability can also result from sampling bias eat?” tends to automatically focus discussion associated with small sample sizes or due to within an unrealistic two-species paradigm of changes in the sex ratio of predators. Predation “seal vs. salmon” rather than placing the rates in the Strait of Georgia are based on discussion within an ecosystem framework. “small” spatial and temporal sampling events Ecosystem interactions need to be considered. and limited seasonal scat collections. This includes knowing the impact that pinnipeds Another important distinction needs to be made have on other prey species that may in turn between ecological and statistical differences benefit salmon, or have indirect effects on other and variation in diet estimates. This entails species complexes. Ecological relationships are recognizing the source of variation in diets, such rarely linear; pinnipeds prey on species which, in as whether most pinnipeds are generalists or turn, prey on other species. specialists. Care must also be taken when To ascertain the potential impact of pinnipeds applying previously collected diet data to project and other predators on populations, better data consumption within a changing environment. are needed on diets, consumption rates, and While small sample sizes can result in huge forage fish populations (e.g., anchovy, sand variances, stratification and targeted collection lance). Stock-specific data to ascertain which of scats can improve precision and, in theory, populations of salmon are being consumed is a provide more specific diet information. The high priority. Unfortunately, analysis of scat observed high variation in diet suggests it will be samples has not identified which runs of salmon very difficult to come up with a generalized are preyed on by pinnipeds. Technologies should (range wide) predation value. be explored to help assess impacts by salmon population unit. Understanding salmon An alternative way to derive a generalized population survival, distribution, and residence predation value might be to focus on small time is important to relate to predation. For spatial scales, concentrating on key areas and

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 11 example, lots of juvenile chinook stay and rear in What else needs to be factored into a full North Puget Sound. Many of these fish are from assessment of predatory impacts of pinnipeds? the Harrison and Chilliwack systems which have In many respects, assessing the impact of been bucking broader trends in declining predation on salmon is a fish question and not a numbers. pinniped question. Pinniped scientists can In addition to studying the top-down effects of determine how much salmon is consumed, but predation on salmon, other studies are fishery scientists are better placed to determine addressing the equally important consideration the impact of this consumption on specific fish of the bottom-up effects of food supply on stocks. These very different questions need juvenile survival. Both hypotheses could explain addressing before considering “what to do about declines of some salmon populations. Food it?” Framing this question within an ecosystem competition affecting body growth and survival perspective may ultimately be the best means to could be exaggerated by hatchery increases into answer this management question. the system. Other fish. Assessing the impact of pinnipeds on salmon cannot be done without considering the Predation on adult salmonids should also be dynamics of other fish species such as herring, carefully evaluated, in addition to the recent hake, and anchovy. These species ultimately focus on juvenile salmon. Just because juvenile affect the rate at which pinnipeds prey on predation occurs does not mean it is a driver of salmon (e.g., via prey buffering) --- and their population trends. abundances can change rapidly in response to Another consideration is that diet is not changes in marine water temperatures, as seen constant, but varies between seasons, years, in recent years. species, etc. — even within a relatively Stock-specific analyses. Additional data are also predictable environment. However, seasonal needed at a stock level for salmon to properly diets are rarely quantified. Year-round estimates evaluate impacts that seals may be having. While of pinniped diets are required for a there is considerable summary data for salmon comprehensive overview of diet, as well as sex at a regional and species level, emphasis needs and age composition of the predator population to be placed on what is happening locally and (which will greatly impact consumption how this relates to what is going on with specific estimates). This level of dietary information is fish stocks. Much of the current stock-specific needed to infer ecosystem interactions, but may data reflects logistical and funding require application of novel methodologies. considerations --- and was never designed to Even less clear (and perhaps more important) is answer ecological and conservation questions. how the diet of pinnipeds changes with changes A localized approach to assessing impacts of in prey base within the local ecosystem (i.e., how pinnipeds on specific stocks of salmon could be much of an opportunist strategy do they use?). done using a 3D hotspot mapping analysis that While prey preference appears to be a learned overlays predicted density surface for pinnipeds behaviour, there is considerable debate over with locations where there are shallow dives whether seals switch to target salmon or (salmon) and deep dives (not salmon). This type whether they are just opportunistic feeders. of analysis could show where salmon are spatially most at risk so that more attention could focus on local effects. It would be a valuable means to evaluate the extent to which

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 12 different levels of predation affect salmon extent to which hatchery and wild fish are dynamics. consumed using current research methods (e.g., PIT tagging), although novel methods (e.g., Scaling up from specific localized instances of thermal marks on otoliths for hatchery predation to an ecosystem-wide effect may be populations) might eventually provide data. challenging or not possible. Facilitating a meaningful analysis will require more data It is possible that the mass release of smolts and about which stocks are not doing well, and how fry from hatcheries buffers wild and hatchery that may overlap with the distributions of salmonids from predation and benefits overall pinnipeds and other predators (e.g., sharks, salmon survival. However, there are equally valid birds, etc.). concerns that hatchery releases create predictable, concentrated prey sources for Other predators. A lack of data on other pinnipeds — essentially reinforcing (bad) predators (e.g., numbers and diet information) is pinniped behaviour. Further experiments could concerning, and tends to bias the discussion be undertaken to evaluate the effects of release towards the better studied pinniped predation. timing and size at age on predation rates. This type of information is important given concern over whether mortality rates are Man-made objects. It is recognized that certain additive or not (additive mortality rates may be man-made objects increase predation potential. appropriate if the rates are converted to For example, artificial haul outs such as log instantaneous mortality). Accounting for the booms, docks, and marine floats can increase extent of predation on salmon by all the major local seal concentrations. Impacts from light predators is critical for assessing potential pollution, specifically on bridges, have been mitigation assessments. recognized as an enabling function for increased salmon predation. Bridges and other structures Role of hatcheries. The role of hatcheries must can physically concentrate fish. The question is, also be considered in an ecological analysis of what (if anything) can be done about these the Salish Sea and predation impacts of objects? pinnipeds. There is pressure to increase hatchery production to provide more adult salmon for Reconciling contrary trends. Finally, it is killer whales, but many key questions regarding recognized that the ecological relationship the impact of hatchery fish remain unanswered. between pinnipeds and salmon is complex and For example, information is needed on whether not nearly as easy to predict as many suggest. there are higher predation rates on hatchery fish For example, returns of chinook salmon to the vs. wild fish. Does the pulse of fish caused by Cowichan River have been increasing since 2009 hatcheries result in densities of fish that are despite being preyed upon as juveniles and more susceptible to predation? This is separate adults by pinnipeds. CPUE of juvenile coho has from the concern that increased hatchery also been increasing since 2011, and increases in releases cause increased competition (and adult coho and chinook have been occurring in decreased survival) among juvenile salmonids. other natal rivers, not just the Cowichan system. This increase in survival needs to be reconciled Differences between predation rates on with the model conclusions that seals are hatchery vs. wild salmonids complicates simple causing population declines. Has there been a assessments of the impact of pinnipeds on change over time in the impact that seals have salmon (hatchery fish typically have lower on salmon? survival rates compared to wild fish). Unfortunately, it is a difficult to separate the

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One possible explanation for the apparent • Use data from well-studied sites for a “disagreement” between increased salmon preliminary assessment of variability and survival and harbour seal predation at local selectivity. Results will help to identify the scales is that the relative abundance of their relative importance of inter-annual variability primary diet items has increased (e.g., herring on model predictions, as well as where data and hake). Basically, pinnipeds might consume collections should be undertaken. It is less salmon when their primary prey is more important to do this to get a concept of the available. sources of variability in the well-studied areas The large herring stock in the Strait of Georgia before moving onto other less-studied areas. • should be a boon for chinook and pinnipeds Predation is one source of mortality on alike. The degree of piscivory in juvenile coho salmonids. Non-predatory sources of and chinook is highly variable and correlated to mortality could be leading to decreasing marine survival. For chinook, the switch from populations of salmon, and could also make euphausiids to piscivory appears to be critical for them more susceptible to predation (e.g., enhanced growth and survival. However, ocean conditions/temps, food availability, substantial levels of piscivory by juvenile disease). Marine survival needs to be linked salmonids has not been observed within the to all of these other factors (not just pinniped Strait of Georgia where chinook are primarily predation). consuming euphausiids. • A model like Atlantis may be the best type of model to account for direct and indirect How can estimates of consumption and effects. However, such models require a lot of predation rates be improved? input data, which has been a struggle for assessing impacts of predation in the Salish Improving predation estimates. Inter-annual Sea. variability is a pervasive “problem” in ecology. It is a major source of uncertainty that needs to be Improving consumption estimates. A number of incorporated into decisions about how data are things are required to improve estimates of used, and how uncertainty in model estimates amounts of salmon consumed by pinnipeds. are expressed. This means including variability of One of the most critical is to calibrate and salmon stock characteristics (numbers, size) into validate the methods used to describe pinniped predictive ecosystem models, as well as diet across the three primary pinniped species. incorporating variability in the abundance of Current methods (a combination of genetic and other prey species (e.g., herring and other forage hard part analysis) have only been partly fish). The general preferred approach is to look validated, and only for harbour seals. It is at data across the years to better understand essential that additional validation studies how this system is changing. But it is important (controlled feeding experiments) be performed to use the right statistical approach. with captive animals to improve diet estimates via scat analysis for Steller (and California) sea A number of things could be done to incorporate lions. and reduce uncertainties in model predictions associated with inter-annual variability. These Even if individual diet estimates are assumed to include: be accurate, there is no consensus on how to weigh habitat and sex-specific diet differences. • Coordinate dietary methodologies used by DFO is partly addressing this by broadening its researchers to better determine size sampling effort, but it will inevitably be limited selectivity (e.g., use of vertebrae from scats).

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by habitat type (especially tidal areas). The been investigating other sources of mortality influence of various types of sampling sites that affect marine survival and decrease salmon needs to be weighed (i.e., a correction factor) to abundance. This includes studies of both get accurate, overall consumption estimates. bottom-up and top-down effects. A majority of the predation studies have been focused on Impact assessments will also be improved by harbour seals due to the correlations between knowing more about both predator and prey increased abundance of seals and concurrent demographics. Most notably: declines in coho, steelhead, and chinook marine • The apparent sex bias in scat analyzed needs survival. However, there are other potential to be addressed, as indicated by the Strait of predators of juvenile salmon such as Humboldt Georgia data. Sex identification can be tested squid, resident salmon, great blue Pacific herons, through captive studies. Pacific harbour porpoise, Pacific white-sided • Refining prey size is also important; both dolphins, Pacific hake, river lamprey, salmon absolute size and growth rates of fish being sharks, sturgeons, tuna, grey and humpback consumed will provide important predation whales, northern fur seals, piscivorous birds, etc. information. It might be possible to look at More information regarding impacts from these otoliths from scats to see if they are feeding on multiple predators could contextualize the slower or faster growing fish. impact of harbour seals and broaden understanding of where salmon are most Collectively, this new information will help affected. identify which component of the fish population is being taken and the indirect effect of other There are a host of environmental factors environmental factors on susceptibility of affecting the rate at which salmon are preyed salmon to predators. upon, which may require greater attention. These include the extent of kelp forests, habitat Would removing pinnipeds increase juvenile complexity, water temperature, stream water salmon survival? height and flow, man-made obstructions to fish Other mechanisms that affect predation. Many passage (bridge, dam, etc.), proximity to believe the basic premise that increasing smolt pinniped haul outs, alternative prey availability, numbers (and their survival) will increase adult fishing efforts, and hatchery fish. However, the returns. However, substantial questions remain indirect effects of these environmental factors regarding the relationship between increased makes it difficult to incorporate them into the number of smolts and smolt-to-adult ratios structure of current predictive models. (SARs). Increasing the number of smolts in the These factors reflect the inherent complexity of system (i.e., through hatchery releases or the ecosystem we are dealing with. Creating a decreased pinniped predation) may increase simplified model will be faster and will yield competition, thereby ultimately lowering ocean “results”, but it is disingenuous and dangerous to survival. This hypothesis is partly backed by assume these predictions will be accurate. research on chinook salmon in other study areas. Compensatory mortality – is it a major factor? Other studies have noted increased marine Additive mortality is when all of the predation in survival in the face of increased predation by the system is independent; i.e., removing a pinnipeds. specific predator means that those prey will not The US-Canada Salish Sea Marine Survival be consumed by other predators in the system. Project (www.marinesurvivalproject.com) has Compensatory mortality refers to the situation

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when the potential prey of a predator that is having samples at the right time and place to removed from the system will be consumed by detect salmon in diets, highlighting a gap in other predators or die of other natural causes appropriate study designs. such as disease. The distinction is critical for

predicting how an ecosystem will react to removal of a predator. Next Steps—Resolving There is unlikely to ever be 100% compensatory Uncertainty mortality. In other words, it seems unlikely that all of the juvenile fish eaten by pinnipeds would 1. What are the biggest knowledge gaps that need to be filled to draw sounder conclusions be eaten by another predator in the absence of about the role of pinnipeds in the ecosystem? seals. Instead, some of the morality caused by seals and other predators is likely additive Broader ecosystem considerations mortality (i.e., each predator adds to the A significant knowledge gap identified was a lack increasing total natural mortality rate of of empirical data needed to understand the vast salmon). But how can the degree of array of ecological linkages in the system (Salish compensatory mortality be assessed? Could a Sea). Ecosystem modelling is an important tool comparative study be undertaken to determine for gaining insights into dynamic systems—and there are a number of good predictive the extent to which pinniped-caused mortality is ecosystem modelling approaches that can be additive or compensatory? used. However, real-world data is required to The level of compensatory mortality may vary evaluate which models are most appropriate and depending on how the fish behave and how accurate. This is needed to improve healthy they are. Do they quickly pass through understanding of the biological and physical areas where seals feed or are they more resident drivers that affect salmon populations so that in areas where predation risk is high? The range educated decisions can be made regarding the results of altering aspects of the system. of possibilities may make it difficult to determine susceptibility to predation. Furthermore, the It is important to recognize that there are likely behaviour of the fish may be stage-specific and factors not yet considered that are more may vary between years. important than pinniped populations in driving salmon declines. Environmental factors, for Anecdotal data does not show seals causing a lot example, can be major drivers of salmon of mortality of larger juvenile salmon, which populations—but may not affect all stocks of raises the question of “who is eating them – and salmon alike. when and where is it occurring?” It is a knowledge gap that is important for accurately Drivers of salmon populations are not limited to predicting the potential effect of changes in predation, but are likely a combination of pinniped numbers. interacting factors that differ between regions and salmon stocks. However, the spatial scale Large adult hake or other large predatory fish that is the most appropriate for understanding (possibly salmon shark or some other these interactions is unclear. Determining the unconsidered predator) could be a large appropriate scale would help determine the component of subadult mortality. Other appropriate level of management interventions. pinnipeds and marine mammals (harbour porpoise, white sided dolphin, etc.) could also A broad examination of all salmon mortality contribute to potential compensatory mortality. factors is necessary to properly assess the impact The lack of data might partly be due to not that seals may be having on salmon (e.g.,

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dynamics of other fish stocks, other predators, their numbers can change quickly in time and environmental change). The proportion of space (vs. seals). This is particularly true for salmon mortality that is directly caused by California sea lions whose movement patterns predation also needs careful examination. The are not understood. Pinniped census counts focus also needs to be widened beyond just have tended to focus on harbour seals and harbour seals. Questions to address include: Steller sea lions at marine sites. Census counts should be extended to riverine systems for all • What impacts are others consumers of species. salmon (e.g., herons, cormorants, mergansers, and fish) having in estuaries? It is a tremendous effort to survey all pinniped • How much salmon are other predators haulout sites. Counting at index sites may be a consuming (e.g., other fish, Steller sea lions way to offset this. They can be appropriate for and other marine mammals) once salmon “stable” populations, such as harbour seals in leave the estuary? the Strait of Georgia. However, existing • What predation patterns (e.g., areas where uncertainty with population estimates and predation occurs, and age classes of salmon recent information around spatial re-structuring consumed) have the greatest impact on may negate the value of index sites. Most returns? notably, a shift in animals from index sites to non-index sites would appear as a population The spatial-temporal overlap of pinnipeds and decline when one has not occurred. salmonids needs to be determined. This also Consideration needs to be given to the pros and needs to be done for other predators of salmon, cons of using index sites to census pinnipeds in as well as for the prey that salmon feed upon. the Salish Sea. Pinniped numbers and diet A year-round collection of pinniped scats is Having accurate population estimates of necessary to obtain a comprehensive description pinnipeds is essential for determining predation of diet. Although increasing numbers of scats are impacts on salmon. Canadian harbour seal being collected, there are always practical and estimates are reasonable, but surveys need to financial limits. increase on the US side of the border. In addition, the spatial expansion of harbour seals Basin-wide impacts of pinnipeds on salmon are outside of the Strait of Georgia should be re- being estimated from small samples of diet evaluated to derive a more accurate population samples. These small samples ultimately lead to estimate. uncertainty and low confidence in predicted impacts due to the possibility that they are The Strait of Georgia harbour seal population is biased by age, sex, or sampling location—and believed to be stable, which raises the question are therefore not representative of the average of what is limiting harbour seal abundance in this seal diets. For example, genetic information area. The seals do not appear to be limited by suggests a disproportionate (~3:1) number of food given there are no signs of malnutrition or male scats being collected in some areas. poor body condition. Predation by transient killer whales is a reasonable explanation given Scat sampling can give a snapshot of prey intake, the frequency with which they occur in the Salish but does not reveal anything about the dynamics Sea. between predator and prey. For example, it cannot be used to infer the degree of size Surveys of sea lions also need to be done more selectivity by pinnipeds—in the absence of frequently—perhaps even monthly given that

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information about the sizes of potential prey needed to evaluate management options will available to them. help define the sampling regime. The remains of salmon contained in seal scats For consistency, spatial sampling units should be also cannot yet by broken down to salmon agreed upon between Canada and the USA—and conservation units. New technologies may sampling designs should not just be for salmon. ultimately help refine the estimate of impacts by Recent increases in abundances of forage fish (e.g., anchovy) have been observed. Obtaining salmon population units. information on forage fish populations should be Fish dynamics a priority. Hatchery salmon typically experience higher Not enough is known yet about the interaction marine mortality rates than wild salmon, which between predators and salmon populations. means that it is possible that hatchery fish are Some of the major outstanding questions inflating estimated rates of predation for wild include: fish. Resident chinook and coho may also be • Which fish life-history stage targeted by disproportionately present in seal scats, and lead pinnipeds has the greatest impact on to incorrect conclusions about rates of predation overall population salmon numbers and on hatchery and wild fish. Thus, wild and harvest levels? hatchery fish, and resident and non-resident • What is more important for salmonid salmonids may experience different levels of population survival—predation on smolts predation based on having different behaviours or adults? and life histories. • What proportion of pinniped populations are salmon specialists—and are they smolt Resolving why mortality rates differ between or adult specialists or both? salmon stocks is needed to predict what would • Is predation by pinnipeds on salmon happen if pinniped predation is altered through additive or compensatory—and how would culls or removals. Similarly, understanding the ecosystem change if it is compensatory whether predation by pinnipeds is additive mortality and pinnipeds were removed? mortality is needed to determine the level of seal removal that would make a significant Important clues to help answer these questions difference. might be found by looking at all trajectories of different fish populations and determining Continued focus is also needed on stock-specific whether they are explained by pinniped trends (and underlying causes) of marine predation. For example, there is some evidence survival. In particular, a better understanding is that the dynamics of herring are bottom-up needed of the mechanisms that affect the driven, such that top-down effects play less of a relationships between smolt numbers and adult role in controlling their numbers. However, returns. some have expressed the view that top-down It is currently only possible to determine the effects of predation may explain declines in sizes spatial and temporal aspects of salmon biology and ages of herring. (by species) at certain points in their life- There is also a broader question of “When do histories. Filling in more of the missing pieces will you have enough information to do an require greater surveying effort and experiment?” General trends in ecosystem consideration of how to spatially stratify the way interactions will start to emerge as ecosystem in which samples are collected (e.g., rivers, models continue to be developed, but care must basins, Management Areas, habitat types, and be taken not to extrapolate on too general a oceanographic features). Identifying the data level.

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2. How can the impact of predation by seals on In theory, hind-casting models can identify what salmon be assessed without doing an other sources of mortality exist and put experiment? predation into context. It is important to There was a general consensus that data are recognize, however, that extrapolating insufficient at this time to make defensible relationships based on historic patterns and time model predictions and undertake a broad culling series may be compromised by changing experiment. Making reliable predictions environmental conditions (e.g., climate change). requires a better understanding of indirect There may also be limited historic data to effects of culling, food web relationships, and analyze. the factors that influence the major components However, even if such improved models were of the ecosystem. developed, the following must be considered Ecosystem models need to be developed and before any test cull could be implemented: refined to include: • What threshold of uncertainty is acceptable • freshwater survival by management? In all likelihood, the • fishing removals threshold for this type of management • reduced pinniped levels action will be higher than for other (non- • stage-specific mortalities of salmon lethal) types; and • • life-history variance of salmon (resident How can the inherent model uncertainties and non-resident fish) be reduced to meet the threshold of • changes in diet pattern based on habitat confidence required by management? conditions, forage fish availability, etc. Mathematical models are the only way to assess One means to better understand ecosystem the impact of predation by seals on salmon processes is to construct historical (back-casting) without doing an experiment. However, the models. It may also be possible to take general consensus is that there is too much advantage of “natural experiments” that are uncertainty at this time in the current data to created by either temporal changes in conditions yield reliable predictions. or defined differences between locations such as: 3. What experiment could be done and what is the time frame to assess the outcome? • changes in transient killer whale distribution There are four types of experiments that could • warm water events be done involving a) varying hatchery • known changes in forage fish (prey) species production, b) enhancing fish survival, c) non- • survival of fish populations exposed to seals lethal removal of pinnipeds, and d) lethal vs. those not exposed to seals removal of pinnipeds. All require power • west coast of Vancouver Island vs. other analyses of effect size of a given experimental areas change (and time), and the sampling • inland waters vs. coastal requirements to detect efficacy. All also require careful thought about how the ecosystem will be • changes in hatchery releases to test if buffering of other fish have a negative effectively monitored to track changing impact on salmonids dynamics—as well as the time and cost of doing so. • historic seal removals, e.g., Puntledge River and historic bounty program.

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Vary hatchery production that decrease survival and increase predation Hatcheries provide a relatively easy means to risk might also be modified or removed. experimentally manipulate the system, Deploying PIT tags in young salmon is one means particularly as plans are already in place for to get a clearer picture of when mortality occurs increasing production. For example, there are during the ocean phase. This would facilitate plans for potential massive increase in hatchery properly partitioning mortality, particularly if smolt production in Puget Sound. These actions combined with better detection (i.e., antennae) can be used as an opportunity to further adjacent to pinniped haulouts. understand the system, with the appreciation that they may not actually be an effective Non-lethal removal of pinnipeds solution. As an alternate to culling pinnipeds, non-lethal methods that involve capturing or harassing Instead of culling pinnipeds, more fish can be pinnipeds could be used to mediate their added to the system to see if marine survival predation impact. Experimental designs could stays constant or if it continues to decline. aim to disrupt the effect of pinniped predation at Hatchery experiments can involve not just certain critical times, such as during a pulse of altering overall output but also shifting timing wild and/or hatchery fish. Actions could also be and location of releases (including level of pulse). site-specific. For example, pinnipeds might be It is important to recognize that such excluded from certain west-coast Vancouver experiments may have unintended inlets, but allowed in others. consequences. For example, increased releases may increase competition, and actually Any such action would need to be viewed as an ultimately decrease marine survival. Therefore, experiment, and therefore would need to have a an alternative experiment might be to reduce control to determine potential success and hatchery production to see if it reduces better understand salmon stocks. A downside to competition with wild fish and enhances the experiments that harass or move pinnipeds body growth and survival of wild salmon. around is that they likely cause ‘downstream effects’ (i.e., predation is shifted to other While such hatchery experiments can provide locations). insight into how the fish interact in the ecosystem, it is important to also consider how Potential non-lethal actions include acoustic the effect of such manipulations in relation to deterrence, particularly at bottlenecks. the ecosystem can be monitored. However, acoustic deterrents have not been too effective so far. In theory, something could be Enhance fish survival designed that is specific to pinnipeds, and would Fish numbers can be increased via increased have to be implemented on a schedule that survival, and not just by increasing the number minimizes habituation. Removing or disrupting of fish entering the system. Experimental haulouts in select places, including log boom changes to the physical environment can be removal, might be an effective strategy, undertaken to measure their effect on survival particularly near estuaries. and returns. For example, kelp cover or other natural suitable habitat could be increased, or Contraceptives might be used as an alternate artificial reefs could be built to increase hiding way of controlling overall population numbers. places and forage fish spawning habitat. Artificial However, if used on juveniles, there might be barriers or pinch points (e.g., Hood Canal Bridge) semi-permanent effects (lessons from eastern Canada studies should be heeded).

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Lethal removal of pinnipeds An experimental lethal removal will entail killing A cull would remove a percentage of all Salish large numbers of pinnipeds in urbanized areas in sea pinnipeds (i.e., decrease the population by the Salish Sea. Such actions would also have to fixed amount that does not threaten the long- satisfy UNEP protocols for justification. term existence of the species). Modelling suggests an initial 50% reduction, plus killing 4. What are the research priorities going 3,000 animals per year for harbour seals is forward? required to increase numbers of returning adult Research priorities to address the most pressing salmonids. A short-term removal would be scientific knowledge gaps were identified followed by monitoring smolt-to-adult return through group discussions. They were not ratios in multiple locations (e.g., in Quatsino, prioritized, and do not necessarily represent a Nisqually). consensus. They include:

Experiments require replicates and controls for Pinniped abundance comparison to evaluate the effectiveness of the • Undertake California sea lion counts experiment. Lethal removals similarly require (important for regional impact) some sort of control to determine whether the • Determine abundance and distribution of removals produced the intended effect. The pinnipeds cross-boundary (surveys) timeline to evaluate the effectiveness of killing • Maintain long-term pinniped abundance pinnipeds should be 8-10 years, or longer if time-series compensatory mortality occurs (i.e., other Pinniped diet predators consume the fish that pinnipeds would have taken). This requires good planning • Obtain Steller sea lion diet information, and resources. with attention to stocks, areas • Refine diet assessment methods (including The potential impact of the action would have to identifying biases) be evaluated by comparing similar systems (e.g., • Develop corrections for DNA diet Nanaimo vs Cowichan). It will also require an in- techniques using captive sea lion studies depth monitoring program with associated • Analyze prey clustering – provides insight increase in effort. For example, the current seal into ecology and predation effects assessment surveys done every 5 years would be • Conduct a meta-analysis of all existing diet inadequate for population level monitoring of information (including cross boundary any such experiment. analysis) • Evaluate size selectivity In addition to removing pinnipeds, it may also be • Assess sex ratio bias of scat collections— necessary to concurrently remove other validate using captive studies; also use predators from the system (i.e., herons, alternate data to understand ratio of actual mergansers, otters, raccoons, and trout). population Considerations might also be given to using different approaches for in-river, in-estuary, and Impact of predation on salmon in-ocean predation. River systems where stocks • Initiate studies to better track predation on are nearing extinction and where seal predation salmon stock - genetics, microchemistry, is occurring (such as predation of steelhead on others? the Gould River) could provide a more “closed” • Deploy pop up tags to follow the fate of system for study. salmon (not just pinniped predation, but other sources too)

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• Assess stock-specific vulnerability to predation • Build spatial models of predator and prey distributions • Survey for presence and impacts of pinnipeds in fresh water • Map broader ecological linkages • Determine roles of different pinnipeds and other predators—and obtain information on demographics and diet info (prime example: Steller sea lions) • Use a management strategy evaluation (MSE framework) to design and test candidate management approaches that might be taken to increase marine survival of salmonids • Undertake small scale removals of pinnipeds in conjunction with paired studies of appropriate control population systems. • Identify predation hotspots using predictive models

A possible next step to refine these lists is to conduct a comprehensive survey of scientists and managers to prioritize and more clearly define the research questions and issues raised during this workshop—as well as to rank the research priorities.

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Conclusions Future Refinement and Planning What Actions to Take This workshop was a first step in bringing together scientists and managers with pinniped The four discussion groups had evenly balanced and salmon expertise from Canada and the expertise on pinnipeds, chinook salmon, and United States to identify and evaluate the impact fisheries management — and came to similar that pinnipeds may be having on salmonids. conclusions regarding key uncertainties that prevent drawing definitive conclusions about the Going forward will require focused research to impact of pinnipeds on salmon. address the key uncertainties that prevent drawing definitive conclusions about the role Some of the recommendations to reduce that pinnipeds are playing in shaping the uncertainty included greater transboundary dynamics of salmonids and other species in the coordination for aerial counts, counting in rivers, Salish Sea. and updating correction factors to get more precise estimates by region and age-classes. Better data are also needed on diets, Acknowledgements consumption rates, and forage fish populations. The original concept for this workshop was to It is particularly important to obtain stock- synthesize the considerable body of research specific data to ascertain which populations of funded by the Salish Sea Marine Survival Project salmon are being consumed. Biases in diet on predation by pinnipeds on salmonids. description associated with small sample sizes Interests from managers and scientists from and the sex and age of animals where scats are Fisheries and Oceans Canada and the collected were further identified as research Washington Department of Fish and Wildlife priorities. And finally, consideration needs to be broadened the agenda and led all three to come given to the alternative hypothesis that it is the together to review and assess a much larger bottom-up effects of food supply on juvenile body of knowledge. The workshop was survival that are limiting recovery on salmon. supported by Fisheries and Oceans Canada Careful thought needs to be given to determine through a contract to the UBC Institute for the the top research priorities in light of limited Oceans and Fisheries. We are grateful for the financial resources, the broad scope of identified logistical support provided by Pamela research gaps, and the timeline sought to make Rosenbaum (UBC Marine Mammal Research management decisions. Addressing knowledge Unit). We are also grateful to UBC Earth and gaps needed to inform ecosystem management Oceans Sciences, and to the Institute for the decisions is particularly important. Oceans and Fisheries for providing meeting spaces.

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Appendix A: Participants

Name Affiliation Anderson, Joe Washington Dept. of Fish and Wildlife

Beamish, Dick Fisheries and Oceans Canada (Ret)

Becker, Penny Washington Dept. of Fish and Wildlife

Berejikian, Barry Nat’l Oceanic and Atmospheric Admin

Christensen, Villy University of British Columbia

Couture, Fanny University of British Columbia

Dickison, Jeff Squaxin Natural Resources

Duguid, Will University of Victoria

Freshwater, Cameron Fisheries and Oceans Canada

Fu, Caihong Fisheries and Oceans Canada

Gaydos, Joe SeaDoc Society

Hammill, Michael Fisheries and Oceans Canada

Jackson, Corey Fisheries and Oceans Canada

Jeffries, Steve Washington Dept. of Fish and Wildlife

Jones, Lisa Fisheries and Oceans Canada

Kemp, Iris Long Live the Kings

Kennedy, Eddy Fisheries and Oceans Canada

Luedke, Wilf Fisheries and Oceans Canada

MacConnachie, Sean Fisheries and Oceans Canada

Majewski, Sheena Fisheries and Oceans Canada

McCulloch, Mike British Columbia Fish and Wildlife

Nelson, Ben Nat’l Oceanic and Atmospheric Admin

Neville, Chrys Fisheries and Oceans Canada

Nordstrom, Chad Fisheries and Oceans Canada

Oldford, Greig University of British Columbia

Olesiuk, Peter Fisheries and Oceans Canada (Ret)

Pearsall, Isobel Pacific Salmon Foundation

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 24 Pearson, Scott Washington Dept. of Fish and Wildlife

Pellett, Kevin Fisheries and Oceans Canada

Rosen, David Ocean Wise

Schmidt, Michael Long Live the Kings

Scordino, Jonathan Makah Tribe

Sherker, Zach University of British Columbia

Stenson, Garry Fisheries and Oceans Canada

Szaniszlo, Wendy Fisheries and Oceans Canada

Thomas, Austen SmithRoot

Trites, Andrew University of British Columbia

Tucker, Strahan Fisheries and Oceans Canada

Walters, Carl University of British Columbia

Ward, Eric Nat’l Oceanic and Atmospheric Admin

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 25 Appendix B: Agenda

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Appendix C: Summary of State of Knowledge and Uncertainties

The following summarizes the state of knowledge and uncertainties regarding the population dynamics and diet preferences of harbour seals, Steller sea lions and California sea lion, and their impacts on salmon in the Salish Sea. Bulleted points provided by workshop participants are contained in Appendix D, and are cross-referenced by lettered superscripts.

Pinniped abundance & trends The BC harbour seal population has been stable Harbour seals, Steller sea lions, and California for the past 20 yearsC —but their distribution has sea lions all prey on salmon in the Salish Sea. changed over time. In Washington waters, California and Steller sea lions occur seasonally harbour seals have been generally stable, but in the Salish Sea from August through May, and densities may have fallen in recent years due to are most abundant in central and northern Puget predationA. The most recent counts of seals Sound, and the Strait of Georgia. They may be were done in 2013 in Puget Sound, and in 2014 found year-round on the outer coast of BC and in the Strait of Georgia. Coordinated surveys of WA. In contrast, harbour seals are present year harbour seals will occur this summer (2019) in round in the Salish Sea and along the outer Canada and the United States. coasts. Estimates of numbers of seals in the Salish Sea In the United States, the California sea lion are derived from aerial counts of animals on population only breeds in California—and is haulouts. These counts are multiplied by considered to be within its optimal sustainable correction factors that account for non-visible population range and at or near carrying capacity animals based upon time of day relative to low in recent yearsA,P. They began to occur regularly tideC. The correction factor currently used for in WA and BC in the mid-1960s, and increased correcting Washington surveys was determined from a few hundred to over 3,000 between 1972 30 years ago for a representative sample of adult and 2018A,P. Numbers of California sea lions and immature harbour seals—and needs to be (almost entirely males) and the areas they use in re-evaluated to ensure that it has not changed the Salish Sea vary between years—due to their significantly over time and has not been affected tendency to aggregate where large by killer whale predation. In British Columbia, concentrations of prey occurA. There are often harbour seal counts are corrected by DFO using dramatic fluctuations in numbers of California another method that calculates proportion sea lions at local scales. ashore relative to time of low tide during the Steller sea lions that occur in the Salish Sea are survey (which was also calculated using part of the eastern population of Steller sea lions instruments deployed in the 1990s). With either that range from California to Southeast Alaska. correction method, changes in either human Their breeding populations have been increasing disturbance or transient killer whale foraging since the 1960sP. Like California sea lions, Steller activities could have changed seal haulout sea lions rarely occurred in the Salish Sea prior to behaviour, and ultimately the correction factor. the mid-1960s—but have been occurring in In addition to counting pinnipeds in marine greater number during winter since the 1970s A,B. areas, attention needs to be given to numbers of They are listed as Special Concern in Canada, and seals using rivers and lakes that are not currently were recently delisted from Threatened in the surveyedC. The correction factors only account United StatesP. They have not yet reached for animals in the water that haul out on tidal carrying capacity. haulouts (e.g., Fraser River estuary). Significant

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 31 numbers of seals (from a salmon predation The small percentage of the overall pinniped diet perspective) may be distributed farther upriver made up by salmon smolts (e.g., 1-2% chinook and therefore not accounted for by correction smolts in a given region and month)G factors. There are also likely seals in lakes which extrapolates to a large number of individual fish are not captured by the tidal-site correction when size of fish, numbers of pinnipeds, and factors. energetic demands are accounted for. However, there is considerable variance surrounding the Pinniped diets & trends estimated proportions of smolts consumed. Diets of pinnipeds have been primarily Some of this uncertainty is due to the broadness determined from prey hard parts (bones, teeth, and high variability of diets between sampling scales, cephalopod beaks, etc.) and prey DNA sites. Some of the uncertainty can also be recovered from pinniped fecal samples (scats) attributed to not having collected sufficient scat collected at haulout sites. Some studies have samples to give reliable estimates for species also attempted to assess diets using stable that are consumed in tiny proportions. isotopes and fatty acids. Prey species and their The targeted number of scats collected typically proportions identified in any given scat often reflect costs, ability to obtain samples, and the differ between DNA and hard part analyses, but desired precision of estimating the importance they tend to show consistent results when of a prey species within each sample. It is sample sizes are increased and scat collections generally difficult to collect large numbers of D,F are pooled . harbour seal scats because most haulout sites In the Salish Sea, over 50 species of prey have are tidally washed each day. Accessibility of seal been identified in pinniped scats in a given haulouts differs by time of year, and is regionD,E. However, pinniped diets are particularly challenging during spring when dominated by three families of fish: gadids smolts are entering estuaries. (primarily hake), forage fish (primarily herring Numbers of scats collected in the field typically and sand lance), and salmon (during summer target ~60 samples to accurately determine the and fall). Salmon smolts are consumed by all proportion of species making up >5% of the diet. three species of pinnipeds during spring and However, larger sample sizes (>300 scats) are early summer, but represent a tiny portion of required when trying to accurately estimate total biomass of prey consumed each day by portions of relatively rare species in the diet. In pinnipeds when averaged over a year or within a Washington, samples sizes for harbour seal D given month or season . dietary analyses have been >70 scats, and in In terms of salmon consumption, harbour seals most cases >90. primarily eat adult chum and adult pinks in the Diet methods are generally less accurate for prey fall, and predominantly eat juvenile chinook, species eaten in small proportions—and more coho and sockeye in the spring and early summer accurate for those eaten in greater proportions. F (10-16 cm) . Steller and California sea lions also Accuracy can be improved with larger sample G consume adult chum salmon in the fall . sizes. Steller sea lion diets tend to be dominated by Prey size is also an important consideration that forage fish and gadids with proportions of adult can significantly affect estimates of numbers of salmon increasing in the fall. California sea lions fish consumed. This is particularly pronounced in also consume high proportions of forage fish salmonids such as chinook. Juvenile chinook with high amounts of salmon in the fall—and enter the marine environment at a range of sizes G gadids in the spring . and can reside in the Salish Sea as juveniles, subadults, and adults.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 32 Sizes of fish consumed are best determined by concentrated near some seal haulouts than measuring the lengths of vertebrae and otoliths others. Inappropriately applying the diets from recovered in fecal samples—and then applying one or a few study sites and times to other areas regression equations to derive the and years within the Salish Sea will yield biased corresponding size and weight of fish that were estimates of predation rates. originally eaten. Referencing specific size classes A recently recognized factor that may also over- and habitats where the fish are consumed (e.g. inflate the estimated proportion of salmon in-river, estuary, nearshore, offshore) would smolts consumed is the sex and size of the avoid the ambiguity of broadly categorizing fish predator. Diets differ between male and female as smolts, juveniles, or subadults. pinnipedsP, and between large and small Smolts and subadult salmon are sometimes individual animals. Female harbour seals appear collectively referred to as juveniles. However, to feed closer to shore compared to males, with juvenile salmon have, by definition, undergone larger individuals of both sexes feeding further smoltification while smolts have not. Subadult from shore than smaller individuals. It also fish already in the Salish Sea are joined by smolts appears that males eat more salmon than of the year coming out of rivers in a number of femalesG,P, and that scats are collected more different size ranges—all of which are potential frequently from male seals than from females. prey for pinnipeds. Misclassifying subadults as Of concern is an apparent significant sex bias in smolts in diet estimates will inflate the estimated scat samples analyzed—which can be corrected numbers of smolts actually consumed by seals. in part using DNA to determine the sex of the Attention needs to be given to correctly individual that deposited the scat. determine the sizes and proportion of each life- Optimally, scat samples need to be collected stage of salmon consumed by seals. This is more broadly across the Salish Sea, and important because some “juvenile” fish throughout the year. Dietary analyses may also consumed by pinnipeds may actually be 1-year need to incorporate weighted stratification old fish that stayed in the Salish Sea rather than migrating to the open ocean. Estimates of schemes to account for seasonal and geographic consumption will drop significantly if seals and differences in diet and shifts in the distribution sea lions preferentially eat the larger fish. Size is of animals. A better understanding of pinniped needed to derive reliable estimates of population demographics and the size of prey consumption. consumed are also important. Harbour seals are thought to prefer fish between Prey abundance & trends 10 and 16 cm. A possible length cutoff between the two size categories of juvenile salmonids is Pacific hake and Pacific herring constitute the 12 cm. However, the high variability in size-at- greatest portion of Salish Sea pinniped diets. age of different stocks may mean that there is no Broadly speaking, there has been variation, but simple cutoff between smolts and subadult fish no significant declines in the overall abundance (or fish returning from the ocean). of groundfish over the past 60 years in Puget SoundJ. Overall abundance of herring has also Another concern about the current estimated been stable in recent yearsJ. Regionally, proportions of smolts contained within scats is however, some stocks of herring have declined that may not be representative of seals while others increased. Declines have also throughout the Salish Sea (i.e., site selection may occurred for other forage fish species, as well as be biasing population diet profiles). Diets are true cods and some rockfish species. known to vary significantly by year, season, and location—particularly between estuary and non- In the Strait of Georgia, herring biomass is at all- estuary sites—and smolts may be more time high levels, but spawn distribution has

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 33 changed over timeK. Anchovy, another and exhibit an extensive offshore ocean important forage fish in pinniped diets, has migration). increased in recent yearsK. Range wide (throughout the Northeast Pacific), Five Pacific salmon, as well as steelhead trout, the abundance and size-at-age of the oldest age spend at least some portion of their marine life- classes of chinook have declinedL. Possible history in the Salish Sea. Species, and explanations for the decline in size include size populations within species, exhibit consistent selective predation (killer whales and sea lions), differences in their duration of residence within fisheries (sport and commercial), a changing the Salish Sea, their trends in abundance, and ocean environment and hatchery practices. the available information needed to evaluate In the Strait of Georgia, chinook numbers management actions or conservation status. declined in the late 1970s, coho in the late 1980s, Recent work on chinook, coho, and steelhead sockeye in the late 1990s. There does not appear has shown declines in marine survival or lower to be any connection between the timing of marine survival since the 1980s for many Salish these declines. In general, stocks of salmon that Sea populations compared to coastal have shorter periods of freshwater residence, populations. longer periods of coastal residence, and smaller In terms of juvenile salmonids that are size at marine entry (e.g., chum and pink salmon) consumed by pinnipeds, a proportion of coho currently have better status. L salmon are now remaining resident in the Strait In Puget Sound, hatchery-produced coho salmon of Georgia—a behaviour that has been missing are twice as abundant as naturally-produced for 20 yearsL. In contrast, chinook salmon have fish, and hatchery-reared chinook salmon are much more life-history variation. Those that 10-times more numerically dominant than their spend at least one year in freshwater move wild counterpartsN. Resident chinook and coho quickly through the Salish Sea and travel salmon that rear year-round in Puget Sound offshore (stream-type or yearling)—while those likely have greater exposure to pinniped that spend weeks to months in freshwater predation than do those that leave the Sound for generally tend to rear in estuaries or nearshore extensive offshore migrations. However, marine coastal waters (ocean-type or subyearling)L. survival of the coastal coho populations appears Most of the Salish Sea populations of chinook are to have improved. the ocean-type. These smolt variants generally coincide with adult run timing (with stream-type Naturally-produced chinook smolts migrate from returning during spring and ocean-type January through July. They are initially small in returning during fall). January (~ 4.5 cm), but show consistent growth beginning in April, and eventually reach sizes of In the Strait of Georgia, yearling chinook have ~6–10 cm by JulyN. Hatchery-produced chinook had generally stable survival rates (smolt – age are predominantly released in mid-May; while 2), while the Salish Sea sub-yearling chinook had naturally-produced and hatchery-produced high survival in the 1970s followed by low but coho salmon smolts both migrate mid-April to stable survivalL. mid-MayN. In recent years, numbers of adult chinook Trawl surveys for juvenile fish in the Strait of returning to some east-coast Vancouver Island Georgia over the past 20 years show that coho rivers have been increasing (ocean-type that rear smolts from all stocks mix through the Strait of in coastal marine waters)L, while the early Georgia, and that their numbers are more arriving Fraser River spring chinook have concentrated northward in the fallO. However, declined (stream-type that rear in freshwater the majority of these juvenile coho will migrate

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 34 though Juan de Fuca Strait later that fallO. About seals on shore increases from June to August 30% of coho are of hatchery origin. during the annual pupping season and fall moult. There is no trend in haulout behaviour of Rearing of chinook smolts in the Strait of Georgia subadults, suggesting the change in adult sex is life-history dependent. The majority of ocean- ratios is due to moulting and reproductive type fish will remain and rear through their first behaviour (breeding and pupping)P. summer in stock-specific areas (e.g., Cowichan River smolts rear around the Gulf Islands, Big Steller sea lions (mostly males) move into the Qualicum and Puntledge Rivers around East Salish Sea in late summer/early fall and are Vancouver Island, Chilliwack and Harrison Rivers present in higher numbers during the winter and around the San Juan Islands and Puget Sound, spring, and are largely absent during summer South Thompson River along the mainland side when they return to their rookeries. Male from Fraser up through Malaspina Strait). California sea lions similarly move into the Salish Sea in late summer/early fall and are seen most In June, coho smolts average ~17 cm, chinook frequently during winter and spring. Most leave are ~13 cm, chum are ~12 cm, and pink and by the end of May to return to rookeries in sockeye are ~11 cmO. California with a few individuals remaining in the Survey catches of juvenile chinook are 2–10 Salish Sea during summer P. times greater in Puget Sound than in the Strait of In British Columbia, electronic tags were glued to GeorgiaO. Differences in habitat need to be the fur of 20 harbour seals at the Big Qualicum considered when comparing predation risks River and estuary to document predation of PIT posed by pinnipeds to different salmon stocks in tagged coho smolts released from a hatchery Q,S. different regions of the Salish SeaO. It revealed that most predation occurs in the In Puget Sound, a statistical analysis undertaken evening and night. Four of 20 seals tagged near to identify ecosystem indicators that correlate the hatchery and in the surrounding estuary ate with marine survival of chinook, coho and PIT tagged fish. Over a 9-day period, each seal steelhead marine survivalM found that ate between 10 and 50 smolts per day. Predation freshwater delivery was a poor explanatory was concentrated in the 9 days following release. variable, while those related to predation, Adjusting these estimates for the total number competition, and water quality explained more variance in marine survival (although only 30- of seals present (tagged and untagged) suggests 40% for the best models). Seal abundance was that a relatively small number of seals ate ~6% of an important negative explanatory variable for the hatchery-released coho smolts. all three species. However, seal abundance The tagging study also revealed 4 types of seals explained much more variance in the steelhead (based on different foraging strategies)Q. One trout and coho salmon data (22% and 30%, consisted of seals that that specialized on coho respectively) than it did for Chinook salmon smolts while they were present, and ignored M (<8.6%) . It is important to note that the chinook in the river mouth—while a second methods for estimating SAR (survival) varied group of seals appeared to target larger fish that among the three species, which may account for preyed on chinook smolts near the river mouth. some of the differences in observed The two other seal groups identified did not feed M relationships . at the river mouth in association with the concentrated numbers of smolts, but either Pinniped foraging behaviour remained resident and fed near their main haul- There are differences in the haulout behaviours out sites, or were transient and left the study of male and female seals, and between pups, area all together. subadults, and adults. In Puget Sound, the For estuary-associated harbour seals, there probability of finding adult male and female appears to be individual foraging and diet

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 35 specialization—with a small number of seals (often a major data gap). Resolving the impact of specializing in consuming coho smolts (primarily seals on fish requires the expertise of fishery at dusk)S. Interestingly, these smolt specialists scientists. did not appear to respond to the large pulse of Understanding the impact of other ecosystem smaller-bodied chinook smolts as they entered components on fish populations of concern is the ocean, suggesting some size selectivity. equally critical to properly place seal consumption estimates into the context of prey This tagging study effectively characterized seal population dynamics. For example, capelin and predation on smolts in an estuary, but was fisheries are important drivers of cod condition, unable to effectively characterize smolt mortality and abundance off eastern predation outside of estuaries. Scat data are the Newfoundland—while predation by seals has only means currently available to assess the not been found to significantly impact northern overall impact of harbour seals on juvenile cod stock levels. In contrast, the collapse of salmon. However, diet and foraging behaviour southern groundfish stocks in the Gulf of St. outside of estuaries may also be site specific— Lawrence coupled with high levels of grey seal and not representative of overall Salish Sea predation appears to have created a predator feeding behaviour. pit, where grey seal predation may be limiting the recovery of cod, hake and skate—even in the Perspectives on pinniped impacts on prey absence of fishing. species Rates of predation on salmonids and amounts In eastern Canada, concerns about the impact of consumed by pinnipeds grey seals and harp seals on commercial fish species increased following the collapse of cod in Rates of predation and amounts consumed have the early 1990s. Many of these cod stocks have be calculated at different scales and species U,V,W,X,Y not recovered. Considerable research has been using different data sets and assumptions . undertaken to determine the impact of seal One study postulates that the currently stable T predation on cod . harbour seal population may be much higher The first step to assess the impact of pinnipeds today than it has been for several millennia when W on fish stocks in eastern Canada was to estimate seals were harvested by First Nations . the amounts consumed, which is a function of This study further concludes that three lines of abundance of seals, their energy requirements evidence point to seals as a potential cause of and their diets. In general, numbers of harp and increases in first-ocean-year mortality rates: grey seals are relatively well known and correlative, diet, and seal behaviorW: precise—and tend to be relatively constant from one year to the next. Energy requirements are 1. There is a significant linear correlation also well understood. Most of the uncertainty in between first ocean year mortality rate and estimates of consumption are due to uncertainty seal abundance, for average mortality rates in the proportions of species consumed and how estimated from coded wire tagging for it varies by age, sex and feeding locations of the indicator chinook and coho stocks, as seals. expected if seals take juvenile salmon incidentally while foraging for other prey. The second step in assessing the impact of seals 2. Increases in mortality rate predicted from on fish stocks was to estimate how much of estimates of total juveniles eaten based on natural mortality (M) of fish can be attributed to seal energy requirements and diet seal predation and how much is due to other composition data are highly uncertain, but factors. Ultimately, the impact that seals have on agree broadly with the increases estimated prey populations depends upon the population from correlation studies. dynamics of the prey species, as well as the seasonal distribution of predators and prey

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 36 3. Estimates of potential mortality rate based on A second modelU, using the same diet data, seal foraging behavior (swimming speeds, estimated that seals consume 24% of the reactive distances, foraging times) also juvenile chinook in Puget Sound and 44% of predict the mortality rate increase apparent them in the Strait of Georgia. For coho, the from correlations. model estimates that seals eat 35% of the juvenile coho in Puget Sound and 55% of them in Increases in mortality rates of coho are the Strait of GeorgiaU. Thus, predation rates for consistent with the increase that occurred in seal juvenile chinook and coho appear to be lower in abundance. However, chinook stocks show Puget Sound than in the Strait of GeorgiaU. highly variable responses to seal abundance with the dominant lower Fraser (Harrison) chinook It is important to note that there is high showing about half the change in mortality rates uncertainty and disagreement around these seen in other Georgia Strait indicator stocksW. estimates, and they are subject to change as new data are incorporated and model assumptions Some seal diet data has been interpreted to are refined. show that predation of salmon is not concentrated in estuarine areas, but is spread A field study used acoustic telemetry to assess over the first ocean summer as juvenile salmon predation of steelhead in Puget Sound and Hood disperse widely over the Strait of Georgia and Canal since 2006X. It found an annual variation are exposed to predation by seals from both in survival of smolts ranging from 6% to 38%X— estuarine and non-estuarine haulout sitesW. and concluded that there appears to be a However, concern has been expressed that negative relationship between presence of seals these data from Belle Chain are not and this early marine survival of steelhead representative of non-estuary sites. Scat smolts. collection sites in the San Juan Islands may also Other factors influencing juvenile steelhead be similarly biased. survival include ocean temperatures, anchovy Most of the uncertainty in assessing the impact recruitment, and presence of alternative prey for of seals on salmon is due to uncertainty in the seals to feed on. Predation by killer whales on small proportions of juvenile salmon found in seals may also affect steelhead survival rates by seal scats. Small proportions of salmon in the influencing seal behaviour and their foraging seal diet extrapolate to high predation rates due locationsX. to the energetic requirements of harbour seals, The harbour seals feeding in Puget Sound and their high numbers, and the small body size of the Strait of Georgia likely have different juvenile salmon in the spring and summer foraging ecologies because of basin-specific months U. differences in habitat and prey availabilityU. Current estimates of numbers of coho and Current models do not account for the chinook consumed are sensitive to assumptions movement of seals and salmon between these about the size of juvenile salmon being two regions. A Salish Sea-wide model of the seal consumed, as well as the number of prey population may improve current model (hatchery and wild) that are available and formulations that are based on each region vulnerable to seals after freshwater and post- being a closed spatial box. release mortality has occurredU,V. The estimated Steller sea lions also consume salmon smolts. numbers of salmon eaten would be significantly While smolts comprise a miniscule part of the lower if the sizes of juveniles they are eating are diet in terms of biomass, the consumption larger than currently assumedU,V. In contrast, represents large numbers of smoltsY. However, estimates of consumption would be higher if the impact on chinook stocks is probably freshwater and post-release mortality is higher minimal when viewed in the context of the than currently assumed. Research is underway number of smolts produced, and the number of to improve these estimates. smolts dying before attaining adulthoodY.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 37 Preliminary analyses indicate that Steller sea Pinniped diet analysis shows the proportion of lions are an important predator of adult chinook salmon in the diet of seals sampled in the estuary in British Columbia. Total chinook consumption, is low in the spring (juveniles of all species) and mainly by northern resident killer whales and increases throughout the fall (predominantly Steller sea lions, has increased dramatically over adult chum). The relative importance of chinook, the last four decades, while chinook fishery coho, and chum varies considerably from season catches have declined. Increased consumption to season, and from year to year. The proportion of chinook by predators may explain the of juvenile chinook in the harbour seal diet has declining exploitation rates in chinook fisheries Y. declined since 2012 from a high of ~6%, to a low BB Cowichan focal area—rates of predation of almost zero in 2018 . Juvenile chinook averaged ~2% of the spring and summer diet The Cowichan River is a well-studied system with from 2013-2017BB. These percentages apply to populations of seals and sea lions preying on the small number of seals that feed in the juvenile and adult salmonids. For the past Cowichan estuary and cannot be extrapolated to decade (since 2009), returns of chinook to the the entire Salish Sea population of harbour seals. Z Cowichan have increased . Possible explanations Diets vary by type of site (estuary versus non- for the increase include reduced marine estuary) and by regional differences in habitat exploitation, increased wild fitness (reduced that support different types of fish. hatchery releases), freshwater habitat restoration, and increased marine survival. Pre- Other predators of juvenile salmon that have not fishery abundance is not yet as high as historic been studied as intensively as seals include trout, levels, but the trend is positive. Removing seal sculpins, mergansers, river otters, raccoons, and predation on salmon might further increase Pacific great blue herons. Significant numbers of returns of adult fish Z. PIT tags were detected at a heron rookery near Cowichan River suggesting the birds consumed Four haulouts used by seals that feed in the 1-3% of tagged smolts released in the Cowichan Cowichan estuary were scanned in 2016 and River annually from 2014-2018 DD. Over 95% of 2017 for the presence of PIT tags (implanted into the tags recovered in the Cowichan Bay heronry chinook smolts prior to release in Cowichan Bay were from river-released fish, as opposed to fish and Sansum Narrows). A total of 18 tags were tagged in Cowichan Bay—suggesting that detected up to 40 km from the estuary. These predation by herons likely occurs in the lower 18 tags were from a wide range of tagging sites river and estuary prior to bay residency suggesting that it was not just recently tagged and more vulnerable fish that were consumed Z. Smaller smolts are more susceptible to heron predation, likely as a result of slower migration Juvenile chinook from the Cowichan River speeds, slower predator evasion, and possible appear to be resident in the Gulf Islands through exclusion from refuge habitats by larger smolts September, and are more likely to stay in the when predation is occurring DD. southern Salish Sea for at least the first winter rather than emigrate. This means that they have Tags were evenly distributed under the nests at continued exposure to pinniped predation. the Cowichan Bay heronry, suggesting that most DD Mortality rates appear to be about 40% during herons prey on salmon smolts . the fall and early winter. Pinnipeds may account for at least 18% of mortality during this time of year based on acoustic tagging data AA. It is not known what factors account for the remaining mortality AA.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 38 Factors that affect pinniped predation of offs between conflicting objectives across salmonids management sectors being considered. Artificial lighting and man-made structures may The models are in development, but data facilitate predation by seals on juvenile salmon. limitations may affect each model’s ability to Significant mortality has been documented at accurately model the system and therefore to the Hood Canal floating bridge where the predict the effect of potential management migration of steelhead smolts is slowed and the actions. mortality is particularly high (up to 50% of the The Strait of Georgia is an ideal area for assessing smolts arriving at the bridge)FF. Indirect evidence the top-down effects of pinniped predators on from temperature and depth tags indicate that their prey. Pinniped predation has increased steelhead are being consumed by harbour seals ~20-fold since 1970, and the diet is rather simple at or very near the Hood Canal Bridge, and this (being dominated by two species, herring and predation appears to account for most of the hake, which comprise distinct Strait of Georgia mortalityFF. Higher numbers of seals occurred stocks) II. near the bridge during one of the two years of study—but densities were fairly uniform The increase in pinniped abundance appears to between locations (near and far from the bridge) have resulted in higher mortality of herring, in the second year. If seals are responsible for particularly in older age-classes, presumably most of the mortality, it is likely caused by very because they have higher energy content. The few seals based on the relatively low density of age- and size-composition of hake has also seals near the bridge. shifted toward younger, smaller fish. Size- selective predation by pinnipeds may be driving The presence of transient killer whales may also declines in size-at-age of older herring and hakeII. affect the rate at which salmon are consumed by changing the haulout and hunting behaviours of Seals may have displaced hake as the the seals and sea lions they are targetingEE. Seals predominant herring predator in the Strait of may no longer be able to feed in areas where the Georgia. During the 1970s and early 1980s when risk of predation is highest. Transient killer pinniped populations were depleted, there was whales were rarely seen in the Salish Sea prior to a large biomass of older, larger hake that preyed 2000, and are now seen hunting for marine on juvenile herring and hake. As pinniped mammals on a daily basis. populations recovered, the biomass of older, larger hake was depleted, which reduced Ecosystem considerations predation on juvenile herring and hake, and resulted in improved recruitmentII. Herring There are at least three ecosystem models being biomass has remained at high levels despite the built by three teams of researchers that can be increased consumption by pinnipeds. used to assess food web interactions and the potential consequence of reducing the Herring and hake stocks are currently dominated abundance of pinnipeds on the ecosystem. by younger, faster-growing fish that are more productive. However, this has had negative Individual-based, spatially- and temporally- implications for fisheries that tend to target explicit ecosystem models that simulate the older, larger fish with higher market valueII. whole life cycle of modelled species can reproduce reasonable diet compositions and Predation is usually framed as a negative achieve good understanding of pinniped impacts consequence for prey populations. However, on prey species. predators can benefit the overall health of prey populations by removing sick and unhealthy Such ecosystem models can be used to project individuals that may compete with others or potential future dynamics of fish species and the spread disease. Salish Sea ecosystem under future changes of climate and management strategies with trade- As pursuit divers, pinnipeds are likely to be more successful at capturing individuals that are in

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 39 poorer condition (slow, weak, sick, stressed) Preliminary results of one ecosystem model also compared to those that are larger and healthier. indicate the vulnerabilities of chinook and coho Juvenile fish that are predated may be more to seal predation may be relatively high, lending disease-agent challenged. A study in BC of fish- additional support to hypotheses that disease eating seabirds (rhinoceros auklets) found this to and physiological stressors may be playing an IJ be the case . The juvenile salmon eaten by the important role. birds carried a higher diversity of infectious agents at higher loads compared to fish that were caught using a trawl net.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 40 Appendix D: Participant Presentation Summaries The following synopses of workshop presentations were provided by participants, and have been edited for style.

Day 1 – Pinniped Abundance, Distribution, Sex • SSLs in the Salish Sea originate from and Age Composition, and Seasonal rookeries in AK, BC, WA, OR and CA Movements • In the NW, SSL abundance varies seasonally with peak counts on rookeries A. Pinniped Abundance and Distribution in during summer breeding seasons Washington (Scott Pearson & Steve • In WA, between 1972 and 2017, SSL Jeffries, WDFW) abundance increased from 500 to over Harbour seals in the Salish Sea: 2,000 • In general, Salish Sea harbor seal stocks • During fall, winter and spring SSLs healthy and robust become seasonally abundant where • In US, for management purposes, NOAA there is sufficient prey biomass that may recognizes 3 inland WA harbor seal include herring, hake and adult salmon stocks: Hood Canal Stock, Southern Puget California Sea Lions in the Northwest Sound Stock, Northern Washington • CSLs in OR, WA, BC and SEAK originate at Inland Waters Stock rookeries in the Channel Islands in CA • Under MMPA, WA stocks within OSP (and most likely rookeries in Mexico range (MNP to “k”) waters as well) • In BC, no stock designations but S of • Between 1975 and 2014, the CSL Georgia harbour seal “stock” reached population in US waters, increased from carrying capacity or “k” by late 1990s or an estimated 88,924 animals to 257,606 early 2000s • The US CSL stock was estimated to be • Evidence for stability to decline in inland within its OSP range (between MNPL and WA harbor seal abundance k) • Predation on harbour seals by Bigg’s killer • CSL abundance varies seasonally with whales may be reducing numbers very few in NW waters during summer • Haulout composition varies seasonally by when they are on rookeries in CA and age and sex Mexico Steller sea lions in the Northwest • In late summer/early fall, 60,000 to • WA and BC SSLs belong to the Eastern 80,000 adult and subadult male CSLs Distinct Population Segment (EDPS) disperse north from their rookeries into which ranges along the west coast of waters off OR, WA, BC and SEAK North America from Southeast Alaska to • CSL counts in the WA waters have central California increased from just a few (rare) to over • EDPS was delisted under the ESA and is 3,000 between 1972 and 2018 not designated as depleted under the • During fall, winter and spring SSLs MMPA become seasonally abundant where • Between 1972 and 2017, over its range, there is sufficient prey biomass that may the EDPS has increased from 12,000 to include herring, eulachon, anchovy, hake 79,000 and adult/juvenile salmon • The Optimum Sustainable Population • Predation by CSLs (and SSLs) on ESA listed (OSP) range for SSLs has not been salmon (adults and juveniles) in the estimated Columbia River is significant

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 41 B. Steller Sea Lions: An Important But • Low tide surveys timed towards the end of Unrecognized Salmon Predator (Peter the pupping season (summer) Olesiuk, Pacific Eco-Tech) • Visual scan of entire coastline, reefs • The Eastern Population of Steller sea • B.C. population update scheduled for 2020 lions has increased dramatically in (surveys flown 2014-2019) recent years. In BC and SE Alaska, which • The last coast wide assessment (Olesiuk, accounts for ~80% of pup production, 2010) estimated 105,000 Harbour seals total and pup numbers on rookeries distributed throughout B.C. with slowing have increased 5-fold since 1960. The population growth rate number of breeding sites has grown • The highest density occurs in the Strait of from 4 to 12. The population is now well Georgia; the most recent estimate of above the levels that occurred when the abundance (based on surveys flown in first assessment was conducted in 1913, 2014) was ~39,000 (stable since early-90’s) which was prior to any large-scale kills. • Next survey planned for August 2019; • During the summer breeding season, coordination with WDFW for combined abundance in BC is estimated to be Salish Sea assessment 35,600 – 39,200 as of the most recent • Telemetry based haulout curves used to published survey in 2013. These refine survey parameters (Olesiuk 2010); estimates were obtained by applying new deployments of GPS satellite tags are multipliers derived from life tables to currently underway in Strait of Georgia pup counts, and by estimating the Steller Sea Lions proportion of non-pups at sea and • Aerial surveys undertaken at the end of missed during surveys based on satellite the pupping season (June 27-July 9) for telemetry and archival tags. total breeding population assessments • During winter, abundance in BC • Range wide surveys for the Eastern increases to 48,500 due to an influx of population conducted on a 4 year interval animals from the south displaced in coordination with US counterparts northward from CA and OR by migrating • Latest population estimate (2013) in BC California sea lions, and by an influx of waters: 33,000-39,000 animals in summer animals from the north dispersing from rookeries and haulouts, approx. 48,500 the large rookery at Forrester Island in animals in winter, showing continued SE Alaska. increase • Steller sea lions have emerged as • Last range-wide survey was in 2017; significant predators, and now likely updated abundance estimates scheduled consume more fish and more salmon for early 2020 than any other predator, including California Sea Lions humans. • Breeding season surveys done outside of B.C. C. Pinniped Abundance & Distribution: Strait • Relative overwintering counts updated of Georgia and Coastal British Columbia opportunistically from fall/winter SSL overview: Data limitations, strengths & surveys weaknesses of DFO datasets (Sheena • Counts of CSL observed during 2016/17 Majewski & Strahan Tucker, DFO) survey are scheduled to be finalized fall 2019 Summary of trends Strengths Harbour seals • Coverage: coast wide surveys designed to • Rotational aerial surveys undertaken every estimate abundance of total population 5-10 years throughout BC

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 42 • Regular standardized surveys allow • Increase winter surveys to support diet assessment of trends, range expansions work and support development of more • Log booms? intensive local studies Opportunities • Coordination of surveys for trans- boundary populations • Increased frequency of index site • Longer term dataset (1970s) surveys outside of SOG for harbor seals • Multi-species perspective to validate trends • Use of abundance surveys to inform design • Species specific (i.e. need dedicated CSL) and support interpretation diet studies • Some of our plans-WCVI index site, drone program, further CF Weaknesses/Considerations • Integration with existing data eg NIMML • Current Steller sea lion surveys not brand resights, UBC diet work, past DFO specifically designed to capture growing pinniped datasets and other species CSL overwintering population in B.C. data (correction factors to estimate abundance, • Anticipating questions large groups of swimmers, expanding range) Day 1 – Pinniped Diets and Diet Trends: • Current Harbour seal surveys occur in Seasonal and Inter-Annual Year Variability; summer and are spread over multiple Sex-Based Variability; Specialization years; not designed to capture animals in rivers/estuaries, on log booms; haulout D. Pinniped diets in Washington State (Scott patterns influenced by disturbance and Pearson, Steve Jeffries, Austen Thomas, predation Monique Lance & Bill Walker, WDFW) • Survey correction factors (is haul-out • behavior of seals the same outside the Important analytical and methods SOG); how to deal with log booms and considerations when reconstructing estuaries haulout patterns influenced by pinniped diet: disturbance and predation • Representative sample is critical • Very resource intensive; are there more • Sampling should be designed to effective ways of estimating/monitoring address the specific question being populations and diet addressed. • Relatively little information on genetic • Sample size considerations stock structure and life-history data (recommend considering the take • Need better coordination with NOAA and home messages in Trites and Joy WDFW for transboundary stocks • Representative of appropriate time • No information on abundance and and space potential impacts of Northern fur seals and • Not uncommon to have > 35 species of elephant seals (and other marine mammal prey consumed by pinnipeds in a given species) on fish stocks of interest area • Use of haulout data to design and • However, only 3-15 species are interpret diet studies typically common (represent ≥5% of the diet) Challenges • The uncommon prey are likely being • available resources vs. frequency and consumed opportunistically or coverage represent secondary prey (the prey • survey correction factors found in the GI tract of the targeted • lag time between surveys and prey) publication • Need very large sample sizes of scat (generally > 90 scats per haulout and

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 43 time period (e.g., month)) when trying • Sex and size differences in diet to enumerate prey items less than 5% (females more nearshore, larger of diet. individuals more offshore) • Salmon smolts/juveniles often • Clustering analysis suggests some diet represent less than 5% of diet specialization among individuals or • Important to propagate uncertainty in these results are also consistent with dietary estimates upwards in any specialized foraging bouts but don’t modelling exercise. know if individuals might switch from • Different techniques (e.g., DNA and one particular specialization strategy hard parts) give very different answers to another or to a more generalist on a sample-by-sample basis but are approach because individuals were strongly correlated given an adequate not identified molecularly. sample sizes for a given space and • Different techniques for time. reconstructing diet (QFASA, Stable • DNA provides greater prey species isotopes, frequency of occurrence) resolution but only hard-part analysis can lead to slightly different results. provides prey age/size information. • Our most recent approach using As a result, it is critical to use these two frequency of occurrence information types of information in an integrative in concert with DNA information fashion allows us to estimate the juvenile and • Only DNA can provide information on adult salmon portion of the diet (and the sex of the pinniped that deposited its associated uncertainty) by species. the feces • This study also found the diet to be • Four large efforts to assess harbor seal diet highly diverse (over 57 species of fish in Puget Sound – these have resulted in a and cephalopods) and that juvenile number of government and peer-reviewed salmon represented are relatively publications small portion (generally less than 5%) • Hood Canal Project (1998-2005) – of the overall diet. Frequency of occurrence information from scat E. Food Habits and Diet Overlap of Steller and • Puget Sound (1995, 1997, 2004) – California Sea Lions in Northwest Frequency of occurrence information Washington State (Jonathan Scordino, from scat Makah Tribe) • San Juan Archipelago (2005-2008) – • The Makah Tribe studied California and Frequency of occurrence, stable Steller sea lion diets for two purposes: 1) isotopes, and fatty acids to better understand the role of the sea • S. Puget Sound (2016-2018) – lions in ecosystem to inform ecosystem- Frequency of occurrence and DNA based management and 2) to evaluate if from feces California and Steller sea lions compete for • Some take home information from these the same prey. studies: • 776 Steller sea lion scat and 262 California • Harbor seals have a very diverse diet. sea lion scat were collected from haulouts Critical components = clupeids, gadids, in Northwest Washington from 2010-2013 cottids, and sandlance (year-round), during all months for Steller sea lions and adult salmon (summer/fall) during spring through fall for California sea • Highly variable diet in space and time lions. (year, season, annual and regional • All hard parts found in scat were identified differences along with time-space- to the lowest taxonomic level possible. season interactions) Salmonid bones were further classified by

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 44 size to small (roughly a first ocean salmon, • The greater occurrence of coho than other i.e. smolt), medium (larger than small up salmonid species was consistent across to about 1 kg), and large (>1 kg, assumed size classes and seasons analyzed. to be returning adult salmon). • A large pink salmon year in 2011 resulted • A representative bone of each salmonid in a 1% SSFO increase of salmonid size class from each scat was genetically consumption as compared to 2012. In analyzed to determine species of 2011, pink salmon were the third most salmonid. common salmon species consumed after • Both California and Steller sea lions had coho and chum. diverse diets with 58 prey taxa identified • The high frequency of salmon observed in representing 27 prey families of fish and both sea lion diets is of note because the cephalopods. study area is not near any large salmon • Common prey (>5% split-sample bearing rivers. frequency of occurrence (SSFO)) were in • Observed consumption of species of ranked order for the two sea lions pooled: concern (i.e. rockfish and salmon) was rockfish species, unidentified clupeid, greater than in a previous study that skate species, spiny dogfish, Pacific hake, detected Pacific hake in a much greater Pacific sardine, Pacific herring, and coho portion of diet. This finding suggests that salmon. considerations of Pacific hake abundance • Steller and California sea lions had is important for reducing impacts on significant diet overlap with Morisita-Horn salmon and rockfish by sea lions for Index values of 0.82 in spring, 0.65 in ecosystem-based management. summer, and 0.83 in fall (index values • Modelling is needed to evaluate the greater than 0.6 are considered impact of sea lions on sensitive and significant). economically important species like • Sea lions preyed upon salmonids in all seasons. Steller sea lions had SSFO of salmon and rockfish. Modelling is also salmonids of 15% in winter, 12% in spring, needed to evaluate how impacts on these 6% in summer, and 14% in fall. California sensitive and economically important sea lions had SSFO for salmonids of 11% in species would change if aboriginal groups spring, 12% in summer, and 13% in fall. hunted sea lions as they did pre-European • The majority of bones identified as contact. salmonids were of the medium size class. Steller sea lions had a large portion of bones identified as small (smolt/first F. Harbour seal diet quantification methods ocean year) in the winter and spring. (Austen Thomas, ) California sea lions predated on more • Choice of diet estimation method can large (adult sized) salmon than Steller sea strongly influence consumption estimates lions. • SSFO overestimates prey eaten in low • Genetic tests revealed that coho was the proportion and underestimates prey most commonly consumed salmonid eaten in high proportion species with 5% SSFO in Steller sea lions • We developed a new method with DNA and 5.7% in California sea lions. Chum metabarcoding, using sequence were the next most frequent. Chinook percentages as an index of proportional composed 0.8% SSFO of Steller sea lion consumption: Relative Read Abundance diet and 0.9% of California sea lion diet. (RRA) We were unsuccessful at amplifying 15.2% • Biases in RRA exist but do not strongly of salmon bones analyzed resulting in an influence diet estimates at the population SSFO of 2.2% for Steller sea lions and 1.2% for California sea lions.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 45 level, when averaging a large number of • Seal diet % alone is not very meaningful in samples terms of prey impacts. The numbers are • Life stage of prey consumption is really only informative when converted to a important, especially for salmon. number of prey consumed, and finally • Small percentages of seal diet can equate expressed as a percentage of the total to large numbers of juvenile salmon juvenile salmon mortality consumed • You need to know how many fish were in • We merged data from seal scat DNA and the system to understand seal impact, and prey bones to estimate salmon prey this fluctuates from year to year. Don’t species, proportion of seal diet, and life expect seal diet % to be a static number. stage (Juvenile vs Adult) • > 1200 scat samples analyzed using the method from 3 estuary sites and one non- G. Pinniped diets: spatial, temporal and sex- estuary site based variability (Strahan Tucker, Sheena • Adult salmon eaten were predominantly Majewski, Chad Nordstrom, Wendy Chum and Pink Szaniszlo, DFO) • Juvenile salmon eaten were • Presentation provides an overview of predominantly chinook, coho, and DFO’s scat sampling 2015-2018 and results Sockeye to date (analysis is not yet complete for all • We hypothesize seals are selecting for datasets) and plans to build on and expand juvenile salmon of species that emerge these datasets. from rivers larger (1+yr), and thus fit the • DFO has 3 primary scat-based diet search image similar to a herring forage datasets: 1) spring through late fall fish multispecies collections in the Strait of • Otolith data support that seals consume Georgia, 2) focal 4 season collections for juvenile salmon in the 10-16cm range in Steller sea lions on the WCVI (with the spring/early summer opportunistic sampling of California sea • Buffer prey such as other forage fishes lions), and 3) opportunistic, non-breeding may be very important for juvenile salmon season collections for Steller sea lions. survival in this temporal window • Results are proportional diet estimates • There is concern that our data are skewed based on genetics analysis. Results to date because of the focus on estuaries. This suggest high inter- and intra-specific may lead to overestimation of juvenile variability in diets. Diets are highly variable salmon consumption between seasons and years and at both • Other published data from the San Juan regional (West Coast Vancouver Island vs. Islands suggest similar levels of juvenile Strait of Georgia) and sub-regional (haul salmon consumption in a non-estuary out or estuary vs non-estuary) spatial area. Those data also indicate high levels scales. of juvenile chinook predation relative to • For harbour seals, we have integrated sex other salmon species markers permitting differentiation • Chad Nordstrom presented data beyond between males and females. In all seasons 2012-13 in which the juvenile salmon and locations, diets varied significantly by proportion of seal diet in Cowichan is sex. In part the difference is due to males much lower consuming more salmon. The sex ration is • Fluctuations in seal diet interannually are highly skewed towards males. We likely driven by differences in the number speculate there is a sex bias in haul out of juvenile salmon available to seals from behaviour-but results certainly suggests year to year, and availability of alternative that diet data is biased towards males. prey

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 46 • The proportion (range across all pinniped reconstruction when it is not possible to samples: chinook:0-4.4%; coho: 0.1-4.3%) accurately estimate the number of prey and occurrence (total scats of all pinniped consumed in a meal. SSFO appears to samples: chinook 140 of 2035; coho 83 of provide reliable estimates for fish prey 2035) of chinook and coho salmon was low when compared to volumetric estimates overall with the majority of occurrences in northern fur seals. representing <20% of total diet • Recent captive studies, when corrected for composition. publication errors, indicate that SSFO gives • The Pinniped Research Program continues results comparable to Biomass to make monthly collections of samples Reconstruction. In contrast, Biomass for diet analysis at key index sites around Reconstruction using Nmin as a proxy for Vancouver Island (Strait of Georgia, Queen the number of prey consumed tends to Charlotte Strait, WCVI). Further, we hope exaggerate the importance of larger prey to contribute to a performance evaluation species consumed in small numbers such of the DNA diet metabarcoding approach as adult salmonids. to evaluate the efficiency, sensitivity, • Serious bias can occur when extrapolating specificity and repeatability of the diet from a small number of platform to validate the identification of unrepresentative sites. For example, the 4 species and limits of detection. sites selected by Thomas et al. (2016) for salmon predation studies, which have H. Reconstructing a century of coastal been widely used to estimate diet in the Salish Sea and have been incorporated productivity and predator trophic position into ecosystem models, do not appear to in WA with archival bone (Megan Feddern, be representative of salmon consumption Gordon Holtgrieve, Eric Ward, NOAA ) when compared to the other 54 sites • Early results from harbor seal bone sampled in the 1980s (Olesiuk et al. 1990). analysis: diet/trophic position snapshots • Researchers are encouraged to collect scat over a 100 year period samples broadly and throughout the year, • Baseline productivity estimated from compound specific isotope analyses (CSIA) and to incorporate weighted stratification is correlated with upwelling, and higher in schemes to account for seasonal and inland waters – likely because of human geographic differences in diet and shifts in inputs of nitrogen in these areas the distribution of animals. • The estimated trophic level of seals appears to have declined 1970-1990, and Day 1 – Pinniped Prey Abundance, Trends and may have increased since – because of Availability to Pinnipeds in Salish Sea sparse samples in recent years, these more recent trends are uncertain • Trophic level appears to be higher on the J. Trends in abundance and distribution of coast compared to inland waters gadids and clupeids in Puget Sound and • Harbour seals are estimated to feed lower coastal waters (T. Essington, E. Ng, D. on the food chain with increased Lowry, L. Kuehne, C. Greene, T. Francis, E. upwelling Ward [presenter]), M. Schmidt, P. Dionne, T. Sandell, NOAA) I. Are diet estimates reliable (Peter Olesiuk) • Overall, groundfish trends from the School • Split Sample Frequency of Occurrence, of Fisheries (UW) and WDFW trawl surveys which has been widely adopted for are stable – species are different in their reconstructing diets from scat contents, is variability, synchrony of recruitment based on the concept of biomass dynamics, etc.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 47 • Spatially, the distribution of gadids is • Increased interactions with seine fleet and highest in northern Puget Sound, around California and Steller Sea lions has been the San Juan Islands documented in recent years. • Looking at gadids, clupeids, and perch, there is a slight increase in trophic level of Juvenile Herring Sampling this community since 1987 – though when • An annual survey has been conducted all fish are combined (including more from 1992-2018 (except 1995). numerous spotted ratfish and English • The sampling is conducted a night using a sole), these trends appear to be reversed small purse seine (183 x 27 m). with a decline in trophic level in recent • The survey is conducted at fixed stations years throughout the strait of Georgia. • The largest herring stock in Puget Sound • The survey results inform the stock (Cherry point) has largely declined, as have assessment for herring. several of the smaller ones. The overall • Although CPUE has decreased in recent abundance of herring seems relatively years, body condition has improved. stable in recent years because of an uptick

of the Hood Canal stock. Anchovy • Anchovy are intercepted during the K. A very brief overview of herring, forage fish juvenile survey. and gadids in the Strait of Georgia (Sean • Population appears to be growing in MacConnachie, Jaclyn Cleary, Jennifer recent years. Boldt, Linnea Flostrand, Sean Anderson, DFO) Eulachon Herring Migratory Patterns • Two indices of abundance are collected for • General migratory pattern is for age 2+ Eulachon herring to move out of SOG post spawning o On the WCVI small mesh multispecies (April/May) and move into the west coast bottom trawl survey is conducted feeding areas annually using a fixed station survey • Juvenile herring are thought to remain design. within the Strait of Georgia for the first o The other relative index of abundance is year an Eulachon egg and larval study conducted on the Fraser River from 1995 to 2018 Fraser River Strait of Georgia herring: stock trends and reference points • Herring biomass is assessed using SCUBA L. Trends in Salish Sea Pacific salmon (and surveys, and formerly surface surveys, data complexity in Northeast Pacific assessing the volume and density of eggs chinook salmon) (Cameron Freshwater, deposited during the spawning season. DFO). • Generally spawn distribution has changed • Five Pacific salmon, as well as steelhead over time with increased volumes of trout, spend at least some portion of their spawn over a smaller spatial scale. marine lifespan in the Salish Sea. • Herring biomass in the SOG are at high o Species, and populations within species, time levels. exhibit consistent differences in their • Since the early 1970 fishery has focused on duration of residence within the Salish roe, and more recently food and bait has Sea, their trends in abundance, and the increased. data available to evaluate management or conservation status.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 48 • Species with limited residence within the . Recent return to Salish Sea residence Salish Sea after ~20 year absence. o Generally highly abundant as juveniles o Chinook salmon (May-Sep), then rear offshore in Gulf of . Substantial life-history variation that Alaska until their return migrations (late can most broadly be defined by summer to late fall). freshwater residence o Modest hatchery influences and • Stream-type/yearling: at least one relatively simple fisheries that are year of freshwater residence; mostly near-terminal and commercial. offshore distribution; minimal o Sockeye salmon interactions with southeast Alaskan . Generally 1-2 years of freshwater and northern BC fisheries residence. • Ocean-type/subyearling: weeks to . Dominant stock aggregate in region months of freshwater residence; spawns in Fraser River, which is majority of Salish Sea populations; relatively data-rich. continental shelf distribution; . Status evaluated using trends in considerable interactions with non- productivity (log recruits per terminal fisheries spawner); productivity has declined in . Estimates of status must account for recent decades and return changes in hatchery contributions, abundances have become more differential natural mortality rates, variabile and synchronized among and impacts of multiple fisheries stocks within the aggregate. • Chinook salmon data o Chum and pink salmon o Smolt-to-age 2 survival . Migrate to the marine environment . Derived from coded wire tag shortly after emergence. (CWT) returns that are largely . Although return abundances appear deployed in hatchery fish (in BC) to be more variable, populations . Assume fixed natural mortality within the Salish Sea have not rate after age-2 to calculate first exhibited consistent declines. marine year survival • Species with protracted residence within . Assume marked fish have the Salish Sea representative survival of o Months to multiple years of unmarked fish o freshwater residence o Escapement o Historically components of certain . Confounds wild and hatchery fish stocks remained resident within the in systems where both are present Salish Sea for their entire life cycle and doesn’t account for changes o Relatively large hatchery contributions in management strategy (e.g. and more complex fisheries exploitation rate, hatchery management due to mix of recreational practices) and commercial fisheries that occur . Different suite of indicator stocks throughout marine residence (i.e. not than age-2 survival rates solely near-terminal) o Common trends in survival and o Coho salmon escapement identified using Bayesian . Data on survival is relatively patchy dynamic factor analysis and derived from indicator stocks • Trends in chinook salmon smolt-to-age 2 (mostly hatchery) survival . General decline in Fraser River with o Divided into four life history-region Interior Fraser coho of particular groupings concern

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 49 o Northern yearlings – survival peaked (Kathryn Sobocinski, Correigh Greene, Joe 1990-2000, followed by modest Anderson, Mara Zimmerman, Neala decline Kendall, Michael Schmidt [presenter]) Salish Sea yearlings – generally stable o • Recent work on Chinook and coho salmon survival and steelhead trout has shown a decline in Salish Sea subyearlings – high survival o the marine survival of many Salish Sea in 1970s followed by stable, but low populations that was not evident in survival populations from coastal regions Southern subyearlings – three o (Zimmerman et al. 2015, Ruff et al. 2017, distinct survival stanzas, high in 1970- Kendall et al. 2017). 80s, moderate 1980-90s, and low • The causes of this decline in marine since survival are likely complex, and may • Trends in chinook salmon escapement include bottom-up processes that drive (Salish Sea only) prey availability, top-down processes, Subyearlings – divergent trends with o including increasing abundances of certain systems increasing in recent predators such as harbor seals that may be years (e.g. Cowichan) exacerbating mortality, as well as a Yearlings – precipitous decline since o multitude of anthropogenic factors such as early 2000s habitat loss, contaminants, and hatchery • Changes in chinook salmon demography management practices that may Consistent, range-wide declines in o contribute to disease, reduced fish abundance and size-at-age of oldest condition, and ultimately increased age classes mortality. The cumulative effects of these May be associated with size selective o factors are unknown. predation, fisheries, or hatchery • While the three species with observed practices declines in marine survival have different • Conclusions life-histories, and are therefore subjected Generally populations with shorter o to variable pressures at multiple scales, periods of freshwater residence and there are some commonalities in factors smaller size at marine entry have better explaining marine survival over the 40- status year time period from the late 1970s to Declines in status of species appear o present. uncoupled – chinook in late 70s, coho in • We developed hypotheses related to late 80s, sockeye in late 90s predation, competition, environmental Differences between survival and o variation, and anthropogenic impacts to escapement difficult to disentangle frame our analysis and to identify a suite with current data, but suggest of factors that was best at explaining uncoupling which warrants caution variation in survival time series for when interpreting status populations in Puget Sound, WA, USA. Recent anomalies should be considered o From these hypotheses, we generated . Increased escapement of time series of available and relevant data Vancouver Island chinook salmon; to use as indicators for each hypothesis. declines in escapement of Fraser We used generalized additive modelling to Springs describe variation in survival with multiple . Return to Salish Sea residence of covariates at ocean, regional, and local coho salmon scales. We used smolt-to-adult return ratios (SAR) as the response variable; M. Salish Sea Marine Survival Project: updates to the survival dataset using the ecosystem indicators development methods of Ruff et al. (2017, Chinook) and

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 50 Zimmerman et al. (2015, coho) allowed for communication). To explore the analysis up through ocean entry year 2015. relationship between seal abundance and For each hypothesis we generated survival further, we evaluated univariate multiple generalized additive models and relationships between each species and used best subsets model selection to seal abundance and found that for all identify the combination of indicators species the relationship was negative. explaining the most variance in salmon However, for steelhead trout and coho marine survival. salmon, seal abundance explained much • In general, hypotheses related to more variance in the data (22% and 30%, freshwater delivery performed poorly, respectively) that it did for Chinook salmon while those related to predation, (<8.6%). It is important to note that the competition, and water quality explained methods for estimating SAR (survival) more variance (30-40% for the best varied among the three species, which models). may account for some of the differences in • For Chinook, the factors with strongest observed relationships. support included sea surface temperature • Seal abundance seems to be one in Puget Sound, spring river flow in Puget contributing variable for explaining Sound, seal abundance, subyearling declines in marine survival. However, Chinook hatchery release date, and depending upon the species, other yearling coho hatchery release date. For all indicators are also important. Lack of data except water temperature, the for some potentially important ecological relationship between marine survival and variables (for example, young of the year the indicator was negative. forage fishes in Puget Sound) may limit the • For coho, the variables with the most explanatory power of our models related support included North Pacific Index in the to marine survival. summer (negative relationship with SAR), spring precipitation (negative relationship N. Enumerating availability of juvenile chinook with SAR), stratification in the Strait of and coho salmon to pinnipeds in Puget Juan de Fuca (parabolic relationship), the Sound (Joseph Anderson & Benjamin CV of Chinook subyearling hatchery Nelson, NOAA) release date (positive relationship with • SAR, where the greater the variation in Hatchery-produced chinook salmon release date, the higher survival is), (~10X) and coho salmon (~2X) numerically maximum spring temperature (negative dominant compared to naturally- relationship with SAR), seal abundance produced fish. (negative relationship with SAR), summer • Naturally produced chinook salmon have a NPGO (positive relationship with SAR), and protracted, six month migration from Strait of Georgia herring abundance January through July. Natural-origin (positive relationship with SAR). These chinook salmon are initially small (~ 45 variables collectively hint at numerous mm) but show consistent growth causes of decreased survival for all three beginning in April, and eventually reach species of interest, from unfavorable sizes of ~ 60 - 100 mm by July. ocean conditions, to increased predation • Hatchery produced chinook salmon and prey limitation. predominantly released in mid-May and • For all three species investigated, seal exhibit long term trend toward abundance was an important explanatory synchronization of release dates. variable. The seal abundance time series • Naturally-produced and hatchery- shows a rapid increase until the early produced coho salmon smolts both 1990s when the population has been more migrate approximately mid-April to mid- steady (B. Nelson and S. Pearson, pers. May.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 51 • Seems likely that pinnipeds consume years. The changes are not consistent resident chinook and coho salmon that between species. rear year-round in Puget Sound rather • With the exception of Pacific herring, than migrate to the Pacific Ocean, but the juvenile Pacific salmon are the dominant abundance of these life-histories types is fish in our daytime catch in the surface not commonly estimated. 75m of the Strait of Georgia in June through October. • The dominant salmon species in the Strait O. Juvenile salmon in the Strait of Georgia of Georgia in the summer are chum (Chrys Neville, DFO) salmon and pink salmon in even years. • DFO has been conducting surveys to Chum salmon is typically 2-10 times more study the abundance, distribution and abundant than Chinook or coho salmon. early marine condition of juvenile salmon In the fall, these species are still common in the Strait of Georgia since 1998. The but are more similar in number to coho surveys are conducted in the early and Chinook salmon. summer (late June/early July) and fall • The size of the juvenile salmon in late (September/October) using mid-water June is similar between most species. The trawl gear fished at variable depths from average length over the past 10 years the surface to 60m. During each survey a ranged from 11 to 13 cm for Chinook, standard track line is fished that covers chum, pink and sockeye salmon. Coho the nearshore and deep water regions of are typically 3-5cm larger during this time the strait from Campbell River in the NW period. There has been an increasing to the Canada/US border in the south. trend in length of chinook, coho, chum Other regions (inlets, Gulf Islands, Juan de and pink salmon in the summer months Fuca Strait, Discovery Islands, Puget over the past 6-8 years. The size of Sound) dependent on vessel time and juvenile sockeye is confounded by cycle research questions . year so does not follow this same trend. • Juvenile from all species of Pacific salmon • The abundance of juveniles in the surveys use the Strait of Georgia as an important has been related to returns for some early marine rearing area. The period of species. For example, the abundance of residence varies by species and coho salmon in the fall is related to sometimes stocks but ranges from 6-8 subsequent returns to southern BC the weeks to several months. Some subsequent year (Beamish et al. 2010). individuals/stocks remain resident in the • Juvenile coho salmon are caught in all Strait of Georgia through their first regions of the Strait of Georgia in both marine winter or longer. The majority of surveys although catch rates are typically coho and Chinook salmon remain and higher in the northern regions (Texada rear in the Strait of Georgia until fall or north) in the fall survey. Acoustic tagging later. Conversely, most Fraser River studies indicate that when these fish sockeye salmon rear in the strait for 6-8 migrate out of the strait in the late fall, weeks and then migrate north over a the majority of them will move through narrow time window (weeks) north Juan de Fuca Strait (Chittenden et al. through Johnstone Strait. Refer to 2009). Beamish (2018), Neville and Beamish • Coho salmon historically utilized the (2018), Neville et al (2017), Beamish et al Strait of Georgia both as juveniles and as (2016), Neville et al (2015), Chittenden et sub-adults. Distribution changes al (2009), Beamish et al. (2010). occurred in the 1990s and this species • Over the 20 year time series of the was mostly absent from the region during surveys there have been changes in the their spring of second marine year. abundance of the juveniles between However, in recent years, sub-adult coho

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 52 have returned or have overwintered in marine residence in the SOG with fish the Strait of Georgia and have been that grow faster having increased survival available to sport fishermen in the spring. (Neville unpublished data). We interpret The reason for the change in behaviour this that a bottom up effect is more has not been identified. However, the controlling adult abundance than top abundance of coho salmon in the fall down effects. survey has increased since 2009. • The catch rates of Chinook salmon in Associated with this increase has been an Puget Sound are consistently higher than increase in the size of the individuals. A in the Strait of Georgia (2-10x higher) in hypothesis is that these fish remain in both the summer and fall. It is expected inside waters over the winter as they that the variation is due to the physical have sufficient energy stores to differences with broader and more open successfully remain over the winter waterways in the Strait of Georgia than in months (Neville and Beamish, 2018). Puget Sound. Puget Sound would be • Juvenile Chinook salmon are found more similar to the Discovery Island throughout the Strait of Georgia. region where catch rates can be very high However, there are stock specific rearing for sockeye, pink and chum in mid-June. areas for many stocks where the majority These habitat differences need to be of the stock will remain and rear. Over considered if comparing potential the last decade, the Chilliwack/Harrison predation pressures between the regions Chinook salmon rear primarily in US (Neville unpublished data). water of San Juan Islands and northern • Chum and pink salmon are found Puget Sound and represent only a small throughout the Strait of Georgia in both percentage (~5%) in the Canadian survey the summer and fall surveys. The region (C. Neville unpublished data). odd/even cycle of pink salmon means • The abundance of Chinook salmon is very low catches in odd years and high often similar between the early summer catches in even years. Stock DNA for and fall survey. However, the stock these two species is not as refined as for mixture changes due to an influx of South other salmon species and only identifies Thompson Chinook summer in mid- regions rather than stocks (e.g. Fraser summer (July). The resulting decline in River). Therefore, we have limited stock abundance of other stocks is primarily specific information for these species. due to mortality within the Strait of Catches in the fall indicate that a Georgia as there is no evidence of large component of the fish that entered the movements of these fish out of the Strait Strait of Georgia remain within this inland of Georgia until fall (Chittenden et al. sea, however, we also encounter these 2010, Beamish 2019). fish in other regions including WCVI, QCS, • The CPUE of Chinook salmon in the early Johnstone Strait, and north. summer survey has remained consistent • The early marine period of Chinook over the past eight years suggesting that salmon from the Cowichan River have early marine mortality has not changed or been studied extensively over the past has decreased (if the number of juveniles decade as a focus of the Pacific Salmon entering the ocean has declined due to Foundation Salish Sea Research Program. declining escapement). This stock remains very localized in the • We have evidence that the return region with catch rates remaining highest abundance of UPFR and MUFR Chinook adjacent to the river through August. salmon is strongly related to the However, faster growing and abundance of these juveniles in July (r2= predominantly hatchery fish can be 0.87). Our speculation is that this is a observed in other regions including result of the growth during the early Desolation Sound by mid-summer (C.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 53 Neville unpublished data). Returning • Males eat more salmon than females adults are being examined to determine if • Predation on harbor seals by Bigg’s killer the increased escapement over the past whales has increased in last 10 years and decade to this system is dominated by may be reducing numbers and changing these faster growing, wild Chinook haulout behaviors salmon. • Within the Cowichan estuary (2013-2016) California sea lions chum salmon, Pacific herring, stickleback, • Between 1975 and 2014, the CASL pink salmon and squid have either been population in US waters, increased from in similar or greater abundance to an estimated 88,924 animals to 257,606 juvenile Chinook salmon. Typically, chum • CASLs in OR, WA, BC and SEAK originate at salmon are at least twice as abundant as rookeries in the Channel Islands in CA (and the Chinook salmon. The size of these most likely rookeries in Mexico waters as two species is similar by June (C. Neville well) unpublished data). • CASL abundance varies seasonally with • The catch and abundance of juvenile very few in NW waters during summer salmon in the Strait of Georgia over the when they are on rookeries in CA and past decade shows no evidence of Mexico increasing predation pressure as the • In late summer/early fall, a wave of 60,000 abundance of all species has either been to 80,000 adult and subadult male CASLs steady or increasing. There is evidence of disperse northward from their rookeries shifts in conditions of the juveniles with into waters off OR, WA, BC and SEAK changes in ocean climate over this time • CASL counts in the WA waters have period. increased from just a few (rare) in 1972 to over 3,000 in 2018. • During fall, winter and spring CASLs Day 1 – Pinniped Foraging Behavioural become seasonally abundant where there Diversity, Size Selectivity, and Spatial and is sufficient prey biomass that includes Temporal Differences in Predation Pressure on herring, eulachon, anchovy, hake and Salmonids adult/juvenile salmon • Predation by CASLs (and SSLs) on ESA P. Seasonal changes in harbor seal and sea lion listed salmon (adults and juveniles) in the behavior and abundance in Northwest Columbia River during the spring is waters (Steve Jeffries, WDFW) significant • The US CASL stock was estimated to be

within its OSP range (between MNPL and Harbor seals k) • Haulout space and/or food do not appear

to be limiting factors for Salish Sea harbor Steller sea lions seal populations • Between 1972 and 2017, the EDPS has • Composition of harbor seals on haulout increased from 12,000 to 79,000 sites varies seasonally by age, sex and • Between 1972 and 2017, in WA, SSL location during pupping season, annual abundance has increased from 500 to over molt and availability of prey 2,000 • Relatively small number of scats are • SSLs in the Salish Sea originate from deposited on haulouts compared to rookeries in AK, BC, WA, OR and CA number of animals hauled out (i.e. most • scats deposited in the water) In the NW, SSL abundance varies seasonally with peak counts on rookeries • Male and female harbor seals have during summer breeding seasons with different diets

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 54 relatively small numbers in the Salish Sea • Predation occurs mostly in evening/night. at this time 31 Total PIT tag detections. All in the • During fall, winter and spring SSLs become estuary. seasonally abundant where there is • We limited the consumption estimate sufficient prey biomass that may include expansion to only the estuary seals. herring, hake and adult salmon Consumption likely occurred outside of • WA and BC SSLs belong to the Eastern the estuary but the probability of a tagged Distinct Population Segment (EDPS) which seal and tagged smolt interacting is very ranges along the west coast of North low outside of spatial constriction of the America from Southeast Alaska to central estuary. California • Consumption peaked 4 days after smolt • EDPS was delisted under the ESA and is not release, at ~50 smolts per seal, per day. designated as depleted under the MMPA • This equates to ~1.0 kg/day or 50% of the • The Optimum Sustainable Population seals daily consumption. (OSP) range for SSLs has not been • 96 seals in estuary, 23,786 total smolts estimated eaten, 6.19% of smolt release. • Hassen Allegue’s work on the same animals indicates the seals responded to Q. Using new technologies to quantify juvenile the pulse of 384K coho smolts, but did not salmon predation in the Salish Sea (Austen show a foraging response to 3 million Thomas, Hassen Allegue, Chad Nordstrom, ocean-type chinook juveniles. Andrew Trites) • Overall these data support the idea that seals mainly target larger juvenile salmon • There are clear issues with estimating >10cm, while mostly ignoring the small numbers of juvenile salmon eaten based ocean type Chinook. on seal scat analysis. • Diet data in the SoG suggest the ocean- • We set out to develop an alternative type Chinook may be eaten later method to estimate juvenile salmon (June/July) when they grow into the seal consumption by seals. prey size window (10-16cm). • We developed a head-mounted PIT tag • These data also support the idea that seal scanner for seals that scans the seals predation in estuaries comprises a mouth during foraging to detect PIT tags relatively small portion (~6% of the out- implanted in juvenile salmon. migrating coho) of the overall seal-related • The scanners are accelerometer activated, mortality calculated from scat data (30 – so they only turn on when a seal does a 40%). head-strike to capture fish. • Tank trials with a captive wild seal were used to develop a sampling algorithm that R. Pinniped foraging behavioral diversity, size detects 100% of juvenile salmon eaten in a selectivity, and spatial and temporal large tank. differences in predation pressure on • We deployed 20 devices on seals near the salmonids (Strahan Tucker, Sheena Big Qualicum River, 9 on seals captures in Majewski, Chad Nordstrom, Wendy the estuary and 11 on seals from nearby Szaniszlo, DFO) rocky reef sites. • DFO is undertaking initiatives to address • ~37,000 coho PIT tagged, 19,000 12mm tags, 18,000 23mm tags, 384,000 total elements of foraging patterns and further smolts, Released May 4, 2015. define the spatial and temporal variability in predation pressure on salmonids. • Seal-mounted scanners lasted 2 – 6 • months in terms of battery life. New deployments of GPS satellite tags on harbour seals are currently underway in Strait of Georgia. This is a multiyear project

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 55 with deployments anticipated in other thousands of coho and chinook smolts areas of BC. While the primary objective from the Big Qualicum Hatchery. and impetus of these deployments is to • Comparing the foraging behaviours of provide an updated and precise estimate smolt specialists with non-specialist seals of haul-out correction factor for revealed 4 different foraging strategies. population estimates, half of our tags One consisted of seals (17.6%) that only provide more discrete information on fed on coho smolts and ignored chinook in distribution and foraging behavior. the river mouth, while a second group of • Propose to obtain higher level resolution seals (17.6%) appeared to target larger fish of harbour seal population structure than that preyed on chinook smolts near the currently available through microsatellite river mouth. The two other seal groups did analysis. Harbour seal population not feed at the river mouth in association structure (and sex ratio characterization) with the concentrated numbers of smolts, will be valuable for stock assessments as but either remained resident (52.9%) and current resource management demands fed near their main haul-out sites, or were related to US MMPA require the transient (11.8%) and left the study area all delineation of population management together. units. Current work on characterizing diet • Our results suggest a high degree of composition with metabarcoding will be individual foraging and diet complemented with this technique. The specializations—and show that a small development of an amplicon panel will be number of seals were specialized in used for high-throughput and cost consuming coho smolts (primarily at dusk), efficient screening of scats that have been but did not appear to respond to the large characterized for diet content to identify pulse of the smaller bodied chinook sex, repeat sampling of the individual smolts. animals and assignment to source

population. Day 1 – Perspectives on Pinniped Impacts on • Developing a drone program to address Commercially and Culturally Important Prey variation in haul-out counts. Undertake Species in Eastern Canada frequent drone survey of index haul out sites to address variation in total counts, T. Fisheries Interactions in Atlantic Canada (G. species composition and size-class Stenson & M. Hammill, DFO) composition • Concerns about the impact of seals on commercial fish species have been raised for many decades. However, questions S. Harbour seals: predation on chinook & coho about the impact of grey and harp seals on smolts (Hassen Allegue and Andrew Trites, Atlantic cod stocks in eastern Canada UBC)) increased with the collapse of cod in the • Little attention has been given to early 1990s. Many of these cod stocks understanding where, when and how have not recovered. Considerable harbour seals prey on salmon smolts, and research has been carried out to the extent to which it might be determine the impact of seal predation on opportunistic or specialist feeding cod. From our experience dealing with behaviour by a few or many individual these questions we have found the seals. following: • We documented the spatiotemporal • Consumption is a marine mammal issue – foraging behaviour of harbour seals in the Impact is a fish issue Salish Sea by equipping 17 seals with GPS • Abundance is a major driver of loggers and Daily Diary tags—and tracking consumption estimates. However, the them before and after the release of estimates for harp and grey seals are

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 56 relatively well know and precise. Also Day 2 – Rates of Predation on Salmon and mammal populations generally do not Steelhead and Amounts Consumed by show large interannual variation. Pinnipeds in Salish Sea and Coast • There considerable temporal and spatial variability in diets. Sensitivity analyses U. Quantifying impacts of harbour seal indicate that uncertainty in the diet predation on chinook and coho salmon in accounts for most of uncertainty in the Benjamin Nelson, UBC consumption estimates. the Salish Sea ( ) • Seasonal distribution of predator and prey • Even small proportions of salmon in the are important to quantify to account for seal diet can imply high predation rates. the entire population; this is often a major While there is still uncertainty around data gap several of the key parameters in the • Energy requirements will vary over the bioenergetics models presented here, the year, particularly for capital breeders, and results do show that diet percentage and given seasonal variation in diets, it can the magnitude of predation rates should significantly change estimated not be conflated. In other words, it is consumption of individual prey species. possible that small percentages of juvenile • Things (e.g. diet, body size, distribution) salmon in the seal diet could result in high change over time! predation rates, due to the large energetic • ‘Impact’ depends upon the population requirements of harbour seals, their high dynamics of the prey species. Therefore it abundance, and the small size of juvenile is critical to bring ‘fish people’ into the salmon in the spring and summer months. discussion to estimate how much of M Further, the predation rates are a function (natural mortality) can be attributed to of how many prey are available to seals in seal predation and how much is attributed a given year, which means it is critical that to other factors accurate estimates of hatchery and wild/natural juvenile salmon are known to • Understanding the impact of other make a plausible estimate of ecosystem components is critical in order predation/consumption. to place seal predation into the context of • prey population dynamics Predation rates for both chinook and coho are comparable between the Strait of • The factors influencing the dynamics of Georgia and Puget Sound basins. While different stocks can vary so the important the predation/consumption rates for both drivers may differ species are different, they do appear to be • Capelin and fisheries have been found to comparable in magnitude. We estimated be an important driver of cod condition, the mean consumption of juvenile chinook mortality and abundance off eastern in the Puget Sound was 24%, and 44% in Newfoundland; predation by seals was not the Strait of Georgia. For coho, the mean found to have a significant impact on consumption estimate was 55% in the Northern cod stock levels. Strait of Georgia, and 35% in the Puget • In the southern Gulf of St Lawrence, the Sound. It is important to note that there is collapse of the groundfish stocks coupled high uncertainty around these estimates, with high levels of grey seal predation has and they are subject to change as we created a predator pit, where grey seal continue to incorporate new data, and predation is limiting recovery of cod, hake refine assumptions in the model. & skate, even in the absence of fishing.. • Predation rates are sensitive to model assumptions. Through sensitivity testing, we have concluded that current consumption estimates for both species in both basins are sensitive to assumptions

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 57 about the size of juvenile salmon being body size and hard part morphological consumed, in addition to the number of measurements. prey that are available/vulnerable to seals o Concern over bias against small sized after freshwater/post-release mortality fish due to more rapid digestion of hard has occurred. Larger prey size would lower parts in the seal gut than larger sized estimates of consumption, while higher fish. But two captive field studies freshwater/post-release mortality would suggest the opposite bias, one for increase estimates of consumption. We California sea lions and the other for are currently working with collaborators at harbour seals. Washington Dept. of Fish and Wildlife to o Initial results suggest seals consume improve these estimates. Chinook salmon ranging from 50 to • The Puget Sound and Strait of Georgia are approximately 450 mm. Ongoing effort different, but, they’re also similar. While to identify prey size preferences, given seals in both basins likely have different possible methodological biases in foraging ecology because of factors like sampling. habitat and prey availability, it is • Expressed as a proportion of the total important to note that seals in these two available smolts, our estimates of seal regions—in addition to salmon—are likely consumption of Chinook salmon smolts to move across international boundaries, (see Ben Nelson presentation) is 5 – 70 %, which is not accounted for in the current with a mode of approximately 25%. modelling frameworks. For example, seals o By comparison, total smolt to adult that haul out in the San Juan Islands in the rates for Puget Sound natural and north Puget Sound certainly forage in the hatchery chinook salmon are southern Strait of Georgia, and vice versa. approximately 0 – 1.5%. Thus, ≥ 98.5% Additionally, we know from coded-wire of Puget Sound Chinook salmon smolts tag data and trawl surveys that juvenile die prior to adulthood, and our chinook and coho salmon from Puget estimates of seal consumption account Sound are routinely captured in the Strait for approximately 25% of that of Georgia. Therefore, a Salish Sea-wide mortality. model of the seal population may be an • Efforts to express estimated consumption improvement over current model of juvenile Chinook salmon in terms of formulations that assume each region is adult salmon are fraught with uncertainty essentially a closed spatial box. and major assumptions. o The level of compensatory mortality V. Impact of harbour seals on chinook (Joseph among juvenile salmon is a major source of uncertainty. In other words, Anderson, Scott Pearson and Steve Jeffries, if seal consumption of Chinook salmon WDFW) were somehow reduced, we do not • Our bioenergetic models estimating know how many of the “saved” smolts consumption of Puget Sound juvenile would survive to adulthood, and how Chinook salmon by seals (see Ben Nelson many would be consumed by another presentation) are highly sensitive to predator or succumb to another source assumptions regarding body size of of natural mortality. The Puget Sound juvenile salmon prey consumed. food web is simply too complex for • Ongoing work uses hard part analysis to confident predictions. We suggest that quantify body size of prey consumed. at least some level of compensatory o Otoliths and vertebral bones hold the mortality is likely if the seals are eating most promise for developing salmonid unhealthy or less vigorous fish. species-specific relationships between o Similarly, rates of marine mortality before and after exposure to seals are

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 58 another source of uncertainty in foraging times) also predict the mortality estimating the impact of seal rate increase apparent from correlations consumption of juvenile salmon on the • Coho stocks show consistent patterns of abundance of adult salmon. increase in mortality rate with seal • Assuming rates of total marine mortality abundance, while chinook stocks show approximately similar to current values, highly variable responses with the our estimates of juvenile salmon dominant lower Fraser (Harrison) stock consumed by seals (see Ben Nelson showing about half the response seen in presentation) range from 0 adult salmon other Georgia Strait indicator stocks (assuming 100% compensatory mortality) • Based on diet data, predation mortality to hundreds of thousands of adult salmon rates are not concentrated in estuarine (assuming no compensatory mortality). areas but are spread over the first ocean However, if seal consumption of juvenile summer as juveniles disperse widely over salmon is on the upper end of our estimated range (i.e., 15-25 million) it the Georgia Strait and are exposed to seems unlikely that all of that predation by seals from both estuarine consumption could be replaced by other and non-estuarine haulout sites predators in the absence of seal predation. X. Harbor seal - steelhead interactions in Puget Sound (Barry Berejikian, Megan W. Evidence of high seal predation impact on Moore, Steve Jeffries, WDFW) chinook and coho salmon in the Georgia • Acoustic telemetry research on steelhead Strait (Carl Walters, DFO) trout in Puget Sound and Hood Canal has • The BC seal population is likely much been conducted since 2006 (with a gap higher today than it has been for the last from 2010-2013) and is on-going. Studies several millennia, when seals were have included survival estimation paired harvested by First Nations people with assessments of predation in • Three lines of evidence point to seals as a estuaries, the main basin of Puget Sound, main cause of increases in first-ocean- year mortality rates: correlative, diet, and and fine-scale tracking at the Hood Canal seal behavior Bridge. In 2014 and 2016, harbor seals • There is a strong linear correlation were instrumented with hydrophones, between first ocean year mortality rate acoustic tags, and GPS/TDR tags to and seal abundance, for average quantify interactions with tagged mortality rates estimated from coded steelhead. The following is a very brief wire tagging for indicator chinook and summary of findings: coho stocks, as expected if seals take • Steelhead smolt survival through Puget juvenile salmon incidentally while Sound has varied from 6% to 38%. foraging for other prey • Low survival (2014, 6%) was associated • Increases in mortality rate predicted from with substantial evidence of predation at estimates of total juveniles eaten based Rocky haulouts in Central Puget Sound. on seal bioenergetics and diet High survival (2016, 38%) was associated composition data are highly uncertain, with no evidence of predation at the same but agree broadly with the increases haulout areas. estimated from correlations • Evidence of predation by harbor seals in • Estimates of potential mortality rate the Nisqually estuary (inferred from tag based on seal foraging behavior movement patterns) has increased each (swimming speeds, reactive distances, year and we speculate that it may be related to increasing presence of transient

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 59 killer whales influencing the behavior of • Salmon comprised about 12% of the harbor seals. Peak transient killer whale overall diet, and sea lions consumed an presence in south Puget Sound occurs estimated 17,500 tonnes of salmon during the spring smolt migration period. annually. In the Canadian portion of the • Warm ocean temperatures (PDO) are study area, Steller sea lions consumed conducive to anchovy recruitment in the about twice the biomass of salmon as ocean and survival in Puget Sound. caught in commercial fisheries. • Instantaneous mortality rates (-ln(survival) • Genetic analyses indicate that Steller sea of steelhead smolts are significantly and lions are opportunistic and prey on a wide negatively correlated with PDO (in the variety of salmon species. Some of the year preceding migration) and the one estimates of salmon consumption by index of anchovy abundance available in species appear to be ecologically and/or Puget Sound. economically significant. For example, • It is unknown whether warm ocean Steller sea lions could be consuming conditions have a positive or negative almost one million sockeye salmon in the effect on steelhead after they leave Puget Southern Endowment Area annually, and Sound. Steller sea lions appear to consume more • The presence of alternative, preferred adult chinook salmon than the Southern prey may lessen predation impacts on Resident Killer Whales. These estimates steelhead need to be peer-reviewed and • The Hood Canal floating bridge slows the incorporated into salmon stock migration of steelhead smolts and causes assessments. significant mortality (up to 50% of the • Preliminary analyses indicate that at the smolts arriving at the bridge). ecosystem level (SE Alaska to the Columbia River), Steller sea lions are an important Temperature and depth tags strongly adult chinook predator. Total chinook indicate that steelhead are being consumption, mainly by killer whales and consumed by harbor seals at or very near Steller sea lions, has increased the Hood Canal Bridge, and this predation dramatically over the last 4 decades, appears to account for the most of the whereas chinook catches have shown a mortality. corresponding decline over the same  Except for the extreme southern end of period. Increased consumption of chinook range, abundance of most stocks has not by predators may explain the declining declined in the past 6 years. exploitation rates in chinook fisheries.  Columbia River summer and upriver bright • Steller sea lions also consume salmon smolts. While smolts comprise a miniscule stocks have had recent record high part of the diet in terms of biomass, the abundance. consumption represents large numbers of smolts. While the numbers may appear to Y. Prey requirements and salmon be astronomical, the impact on chinook consumption by Steller sea lions in stocks is probably minimal when viewed in southern British Columbia and Washington the context of the number of smolts State (Peter Olesiuk) produced, and the number of smolts dying • A large-scale assessment in the Pacific before attaining adulthood. Salmon Commission Southern Endowment • Salmon managers should consider Area (Cape Caution to the mouth of the incorporating the growing number of Columbia River but not including the River) salmon removals by predators as part of indicates that Steller sea lions commonly ecosystem-based stock assessment feed on salmon models. This would allow allocation of the

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 60 finite supply of salmon between fisheries (September to March) escapement would and predators and facilitate a discussion of increase 54%. This assumes seal related the tradeoffs of various management mortalities are still occurring before and options (curtailing fisheries versus culling after study period. predators versus recovering threatened • If we assume 18% of all mortalities are due species). to seals from September of the ocean entry year onwards removing that mortality would increase escapement Day 2 – Rates of Predation And Amounts 255% Consumed – Cowichan Focal Area. • If the window is shifted backwards to June (when fish hit “snack size” 100 mm) an18% Z. Cowichan River chinook: population trends reduction in mortality during the marine and survival (Kevin Pellett, DFO) phase would increase escapement 530%. • Chinook escapement to the Cowichan • Ground truthing of seal interactions with River has been increasing since 2009 PIT tagged fish was conducted in 2016 and • Potential contributing factors include: 2017. 18 PIT Tags were detected on 4 haul reduce marine exploitation, increased wild outs up to 40 km from the estuary. Each fitness (reduced hatchery releases), haul out scanned had at least one tag. freshwater habitat restoration (Stoltz Bluff • Taking into account relatively small 2006), increased marine survival numbers of scats on haul outs, detection • Escapement methodology has also probability, proportion of fish tagged and changed – PIT tag based approach consumption rates the expansion factor provides a specific run timing curve for could be very high. each year to accurately expand end of run • ID’s were from a wide range of tagging when fence removed early. We estimate sites suggesting not just recently tagged this could account for a ~+35% increase fish (more vulnerable) were targeted. over standardized run timing curves in • Acoustic study results indicated most fish 2017 and 2018. exit study area to south – no haul outs • The pre-fishery abundance is still not as have been scanned on this route to date. high as historic levels but an increasing More effort scanning haul outs in this area trend is apparent (slide 10). is warranted. • PIT tag based survival work indicates high mortality through first winter AA. 2017 Cowichan chinook salmon acoustic • Paired acoustic/PIT study in 2017 provided tagging study: pinniped predation both survival estimates as well as implications (William Duguid (presenter), proportion of plausible pinniped related Erin Rechisky, Aswea Porter, Francis Juanes, mortalities Kevin Pellett, and David Welch • Good agreement between PIT based • Caveats: Measuring pinniped predation survival estimates and acoustic study was not a primary goal of the study; these results as well as CWT survival to Age 2 conclusions are based on the • Potential ways to double escapement interpretations of Duguid and are subject were explored theoretically. A 7% to revision pending further review of tag reduction in mortality after September of detection details prior to publication of the first marine year was equivalent to results. Select conclusions relevant to doubling smolt production or closing all pinniped predation: marine fisheries. • We experienced some early mortality • If we take acoustic study results at face likely due to tagging and handling, these value and remove observed seal related fish 12/80 were not included in mortality during the study period subsequent mortality estimates

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 61 • Residence of Cowichan River chinook • Salmon consumption inside vs outside salmon in the southern Salish Sea for at the Cowichan estuary in a single year least first winter is likely more common ‘snap-shot’ comparison was: than emigration - This means that these • major in the fall (primarily adult fish) fish have continued exposure to Salish Sea • minor but possibly important in pinniped predation through this period spring (primarily juvenile fish) • We unambiguously estimated high • Annual and seasonal variability influenced (minimum 40%) mortality through fall and diet estimates at a longer term site early winter (Cowichan) across a ‘time-series’ data set • Due to the behaviour of fish in our study (2012-2018) and noted: (extensive milling) pinniped predation was • salmon diet in the Cowichan estuary challenging to unambiguously determine followed an annual pattern (low based on tag movements or final locations; proportions in the spring and that said, our preliminary estimate is that increasing throughout the fall) pinnipeds represented a minimum of 18% BUT of non-tagging related mortality. • the specific seasonal proportion was • Fine scale movement data confirms that highly variable year to year as was the different individual fish within a stock species composition during the exhibit different fine scale distributional spring period (chinook/coho behaviour which may be related to feeding dominated in 2012-13 vs Chum in the (piscivory vs planktivory). This raises the preliminary 2018 data) prospect of growth/survival trade-offs • Overall: mediated by pinniped predation. • Using a single salmon consumption • Suggested areas of required research: value to assess impacts can be • Assessment of the relative degree of misleading (and authors are residence exhibited by different encouraged that the current chinook salmon stocks in the Salish modelling efforts are incorporating Sea... and evidence for changes in variability/uncertainty) residency through time. • Long-term diet monitoring to estimate • Winter ecology of juvenile chinook consumption is the key to correctly salmon in the Salish Sea: Where, how assessing impacts on salmon and deep, what diet, what condition, what other important prey species disease state, and spatiotemporal overlap with pinnipeds CC. Fine-scale catch and effort data with • Trade-offs between growth and emphasis on southern BC areas (Wilf survival - selective implications of Luedke, Bryan Rusch) harvest and predation? • In the Juan de Fuca area recreational BB. Harbour seals consume more adult salmon fisheries were restricted beginning in 2009 in estuaries than elsewhere in the Strait of with greater restrictions starting in 2012 Georgia (Chad Nordstrom (presenter), under ‘Zone Management’ of Fraser spring Sheena Majewski, Austen Thomas, Strahan and summer chinook. Tucker, Andrew Trites) • These restrictions reduced impact on • Salmon consumption is variable in space & larger age 4 and age 5 wild chinook time returning to the Fraser and other areas of • Site selection (field stage) and how those the Salish Sea. sites are later summarized (analysis stage)

influences prey consumption estimates

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 62 DD. Pacific great blue herons: another major with assessments of predation in predator of outmigrating salmon smolts estuaries, the main basin of Puget Sound, (Zachary Sherker (presenter), Kevin Pellet, and fine-scale tracking at the Hood Canal Jamieson Atkinson, Jeramy Damborg, Bridge. In 2014 and 2016, harbor seals Andrew Trites) were instrumented with hydrophones, • Pacific Great Blue herons are a significant acoustic tags, and GPS/TDR tags to predator of outmigrating salmon smolts, quantify interactions with tagged feeding on 1-3% of the tagged smolts steelhead. The following is a very brief released in the Cowichan River annually summary of findings: from 2014-2018. Herons had not been • Steelhead smolt survival through Puget previously identified as a predator of Sound has varied from 6% to 38%. juvenile salmon. • Low survival (2014, 6%) was associated • >95% of the tags recovered in the with substantial evidence of predation at Cowichan Bay heronry were from river Rocky haulouts in Central Puget Sound. released fish, as opposed to fish tagged in High survival (2016, 38%) was associated the estuary, suggesting that predation with no evidence of predation at the same likely occurs prior to bay residency haulout areas. • The highest levels of heron predation • Evidence of predation by harbor seals in occurred in a critically low flow year the Nisqually estuary (inferred from tag (2016). This may be due to the slower movement patterns) has increased each migration speeds of smolts in the year and we speculate that it may be Cowichan River, reduced access to fish related to increasing presence of transient refuge habitat, or a reduced ability to killer whales influencing the behavior of evade heron predation in low water levels. harbor seals. Peak transient killer whale • Smaller smolts are more susceptible to presence in south Puget Sound occurs heron predation, likely as a result of during the spring smolt migration period. slower migration speeds, slower predator • Warm ocean temperatures (PDO) are evasion, and exclusion from refuge conducive to anchovy recruitment in the habitats by larger smolts during predation ocean and survival in Puget Sound. events. • Instantaneous mortality rates of steelhead • Tags were evenly distributed under the smolts (-ln[survival]) are significantly and nests at the Cowichan Bay heronry, negatively correlated with PDO (in the suggesting that most herons take part in year preceding migration) and the one predation on salmon smolts. index of anchovy abundance available in Puget Sound. Day 2 –Factors that Affect Pinniped Predation • It is unknown whether warm ocean of Salmonids conditions have a positive or negative EE. Ecosystem Factors Affecting the Early effect on steelhead after they leave Puget Marine Survival of Puget Sound Steelhead Sound. (Barry Berejikian (presenter), Megan • The presence of alternative, preferred Moore, Steve Jeffries, WDFW) prey may lessen predation impacts on steelhead • Summary of predation by harbor seals on steelhead in Puget Sound and Hood Canal. • Acoustic telemetry research on steelhead FF. Hood Canal bridge assessment: preliminary trout in Puget Sound and Hood Canal has results (Megan Moore, Barry Berejikian been conducted since 2006 (with a gap [presenter]) from 2010-2013) and is on-going. Studies • The Hood Canal floating bridge slows the have included survival estimation paired migration of steelhead smolts and causes

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 63 significant mortality (up to 50% of the constructed using Ecopath-with-Ecosim smolts arriving at the bridge). (EwE) software; Temperature and depth tags strongly • Stock assessments, diet data, indicate that steelhead are being abundance trends, and other available consumed by harbor seals at or very near data were used for 30 functional groups; the Hood Canal Bridge, and this predation • An age structured approach was used for appears to account for the most of the Chinook and coho salmon to capture mortality. important predation changes during the life histories of these species; Day 2 – Ecosystem Considerations: Indirect • The model included the major predators Effects of Pinniped Predation on Salmon and prey of Chinook, coho, and harbour Mortality, Effects of Disease on Predation seals; Rates, and Questions Surrounding Additive and • Several major ecological changes that Compensatory Mortality have been observed were also recreated by the modelling simulation including GG. Spatial and temporal dynamics of recovery of the herring population in the pinniped-prey trophic interactions Strait of Georgia, an exponential growth (Caihong Fu, DFO) of the seal population, and trends in • Observations suggest that pinnipeds are resident killer whale populations; generally opportunistic feeders with • A simulated cull of harbour seals was certain size selectivity. Their diets are then conducted using the model; dependent on spatial and temporal • Results indicated increased abundance overlap with prey species. of Chinook and coho in the absence of • Individual-based, spatially- and harbour seal predation, especially temporally-explicit ecosystem models juvenile fish; that simulate the whole life cycle of • The model is sensitive to several modelled species can produce important factors including the reasonable diet compositions and productivity and diet of hake and achieve good understanding of pinniped present and future predation from impacts on prey species. transient killer whales on seals; • Such ecosystem models can be used to • This model did not replicate results of a project potential future dynamics of fish previous modelling study on the same species and the Salish Sea ecosystem ecosystem (Li et al., 2010) which found under future changes of climate and that the absence of harbour seals management strategies with trade-offs may decrease abundance of commercial between conflicting objectives across fish species (e.g., hake, Chinook); management sectors being considered. • Differences between the modelling results may be accounted for by HH. Seals may not increase exploitable biomass different hake diet and productivity parameter estimates; in the Salish Sea (Greig Oldford, Villy • Future work includes an age-structured Christensen [presenter,] Carl Walters, UBC) parameterization of the model for other • The presentation described ongoing species (herring, seal, etc), spatial activities conducted as part of a Pacific discretion of the model, primary Salmon Foundation activity at UBC, production models and rigorous which is part of the Salish Sea Marine sensitivity analyses Survival Project • A trophic model of the Salish Sea II. Top down effects of pinniped predators on ecosystem from 1966 to 2015 was prey populations in the Strait of Georgia

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 64 (Peter Olesiuk [presenter], Jake Schweigert Central and Northern Coasts. They are and Jaclyn Cleary) pursuit diver which means that in theory, their prey should be more likely to be • The Strait of Georgia is an ideal area for individuals in poorer condition (slow, weak, assessing the top-down effects of pinniped sick, stressed) because are more easily predators on their prey. Pinniped captured. Our juvenile salmon survey was predation has increased ~20-fold since concurrent with sampling at colonies so 1970, the diet is rather simple, being able to contrast the fish consumed with dominated by two species, herring and those available. hake, both of which represent distinct • We provided evidence for both size- stocks in the Strait of Georgia. selective predation and condition based • The increase in pinniped consumption and predation susceptibility of salmon as appears to have resulted in higher mortality both size and condition were significantly of herring, particularly in older age-classes, lower predated salmon than trawl-caught presumably because they’re larger. The salmon. age-composition of hake has also shifted • The proportion of salmon that are small toward younger, smaller fish. Size-selective and in low condition varied substantially predation by pinnipeds may be driving from year to year- a component of this is declines in size-at-age of older herring and thought to be due to ecological factors such hake. as prevailing ocean and feeding conditions. • Seals appear to have displaced hake as the The proportion of salmon in low condition predominant herring predator in the Strait was highly correlated to the timing of of Georgia. During the 1970s and early spring transition. 1980s when pinniped populations were • Disease can also affect condition. We depleted, there was a large biomass of employed a molecular genetic high- older, larger hake that preyed on juvenile throughput quantitative PCR monitoring herring and hake. As pinniped populations platform of 45 different infectious agents recovered, the biomass of older, larger known or suspected to cause disease in hake was depleted, which reduced salmon to see if those that are predated predation on juvenile herring and hake, and tend to be disease-agent challenged. resulted in improved recruitment. Predated fish, relative to trawl caught fish, • Herring and hake stocks are now carried a higher diversity of infectious dominated by younger, faster-growing fish agents at higher loads. We also found an that are more productive, but this has had association with 3 different microparasite negative implications for fisheries that tend species. to target older, larger fish with higher • We also contrasted seasonal pathogenic market value. infectious agents in life-history variants of

juvenile chinook salmon from the Fraser IJ. Juvenile salmon growth performance and River system through the high-throughput vulnerability to predation in marine food quantitative PCR monitoring platform. webs: dynamic links to condition, climate • Life-history variants of Fraser River chinook and infectious disease agents (Strahan salmon currently display divergent stock Tucker, DFO) status with yearling stocks generally in • Seabirds can be ideal models for predation decline and sub-yearling stocks doing studies as some species deliver whole fish comparatively well. to their chicks-so a rare opportunity for us • Variants carried a different infectious agent to actually observe and characterize the profile in terms of (1) diversity, (2) origin or fish which are consumed. Rhinoceros transmission environment of infectious auklets nest at key points along the agents, and (3) prevalence and abundance migration pathways of salmon in BC’s of individual agents. Differences in profiles

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 65 tended to reflect differential timing and fish; this pattern was present for an residence patterns through freshwater, additional five agents in yearling fish only. estuarine and marine habitats. • Similar patterns in diversity are observed in • Shifts in prevalence and load over time other stocks of non-Fraser chinook salmon were examined to identify agents with the utilizing the Salish Sea. At this point we greatest potential for impact at the stock don't know what the fate of any of these level; those displaying concurrent decrease individual fish would be and we did not in prevalence and high load truncation with directly establish links between infectious time. Of those six that had similar patterns agents and disease. However, these results in both variants, five reached higher suggest that agents may play a substantive prevalence in yearling fish while only one role in mortality; a component of which reached higher prevalence in sub-yearling may be increased susceptibility to predation.

Knowledge & Uncertainties about Pinnipeds & Impacts on Salmon—Workshop Proceedings 2019 • page 66

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