Abstracts Stock Assessment, Fisheries Management & Conservation

Abstracts Stock assessment, fisheries management & conservation

14th International Symposium on the Biology and Management of Coregonid Fishes

22 ̶ 26 June 2020 Jyväskylä, Finland Assesment, conservation & management Oral presentation

Capacity of Lake Pyhäjärvi (SW Finland) to support vendace (Coregonus albula) production

1 2 ∗Harri Helminen , Jouko Sarvala 1Centre for Economic Development, Transport and the Environment for Southwest, Finland 2Department of Biology, University of Turku, FI-20014 Turku, Finland, Finland Lake Pyhäjärvi (SW Finland) has been famous for its highfi sh yields for long. The main cause for the ex- ceptionally high vendace (Coregonus albula) yields turned out to be simply a very efficientfi shery. Vendace in Pyhäjärvi grow rapidly: youngfi sh usually attain a length of 13-16 cm during thefi rst year. Up to 90 % of the 0+ vendace are usually harvested in theirfi rst winter. Here we try to estimate the capacity of Pyhäjärvi to support vendace production under changing circumstances. Vendace year-class sizes and growth are known from early 1970s until 2019. During this period Pyhäjärvi has slowly eutrophicated: the P content of water has increased from< 15µg/l to about 20µg/l, and chlorophyll-a from 4-5 to nearly 9µg/l. During 1973-2018 the annual maximum total biomasses of 0+ vendace in Pyhäjärvi reached about 300 tn (20 kg/ha). Due to overfishing, in 1990-1999 the biomass was only about 150 tn (10 kg/ha). When thefi shing pressure was re- laxed, vendace biomass rose again but remained smaller than before 1990, at about 200 tn (13 kg/ha). During eutrophication, roach and perch have increased, and their food competition might be the reason for the reduced biomass of vendace. Assesment, conservation & management Oral presentation

Compensation of regulation induced whiteﬁ sh catch losses with stocking in Lake Inari, northern Finland

∗Teuvo Niva, Sari Raineva, Markku Vaajala, Ari Savikko Natural Resources Institute Finland, Finland The natural Lake Inari supported large commercialfi sheries before the WW2. Due to regulation whitefish catch decreased from 145 tons to 48 tons in the 1960’s. Large scale stocking of whitefish for compensating catch losses begun in late 70’s. All stockings of whitefish have been done with one-summer-old (0+)fi sh, on average 800 000fi sh per year. In the beginning of 2000’s mass marking of the entire hatchery production begun, which made possible to identify if afi sh was originated from natural reproduction or from the stocking. Proportion of stocked whitefish in the catch has varied from 19 to 37 %, average being 28 %. Stocking success was on average 22,0 kg per 1000 stocked whitefi sh. Catch of stocked whitefi sh was on average 16,1 metric tons out of 78 tons of total catch. In summary, catch compensation of Lake Inari whitefi sh with large scale stocking program has not been successful. Compensation target was approximately 97 metric tons, but only 16 tons were realized. It is likely that regulation of Lake Inari has resulted in permanently lower makrozoobenthos production in the littoral zone of the lake, i.e. food shortage of sparsely raked whitefish that is a bottom feeder. Assesment, conservation & management Oral presentation

Estimation of sustainable harvests of Great Slave Lake Inconnu, Stenodus leucichthys, using data limited models.

∗M. Yamin Janjua, Ross Tallman Fisheries and Oceans Canada, Canada Great Slave Lake Inconnu, Stenodus leucichthys, has been under intensive management since the 1980s. The harvest occurs within a much larger multispeciesﬁ shery on Great Slave Lake. The stock is managed since 2012 within the Fisheries and Oceans Canada Precautionary Approach Framework (PA) providing limit reference points. However, the rapid development of data limited models for assessing harvest sustainability occurred subsequent to the initial PA for the stock. We apply various data limited modeling techniques such Depletion Correct Average Catch, Catch- MSY and DMLtools to examine the status of the Great Slave Lake stock and suggest sustainable harvest levels going forward. We propose new limit reference points incorporating the entire catch series for this stock. Preliminary results suggest that the expectations and targets for recovery of this stock may be too ambitious. Assesment, conservation & management Oral presentation

Fast somatic growth may cause recruitment overﬁshing in vendace (Coregonus albula) gillnet ﬁsheries

1 1 2 ∗Thomas Wanke , Uwe Brämick , Thomas Mehner 1Institute of Inland Fisheries Potsdam, Germany 2Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Germany Vendace (Coregonus albula Linnaeus) is commonly assumed at low risk to recruitment overfishing. This as- sumption was confirmed for boreal stocks but might not apply for stocks at lower latitude, where natural conditions are less favourable for recruitment. This study evaluated the risk of recruitment overfishing at the most southern distribution area (Germany) by comparing fecundity, natural mortality andfi shing mortality from two stocks of contrasting growth with an unfished population over three years. Fast somatic growth in one lake resulted from high lake productivity and low stock density, which in turn impaired the stock‘s recruitment potential by reduced egg survival and low number of spawners. Furthermore, fast-growing vendace had substantially higher age-specific fecundity, but this compensatory effect was eroded, because intensefi sheries harvested about 44% of vendace beforefi rst spawning. In contrast, in the slow-growing stock vendace entered thefi shery afterfi rst spawning and the resulting egg production per recruit was similar to that of the unfished population. It is concluded that vendace stocks characterized by fast somatic growth have a higher risk of recruitment overfishing, which can be significantly reduced by protectingfi rst-time spawners from harvest, an aspect that is often overlooked in vendace gillnetfi sheries in Northern Germany. Assesment, conservation & management Oral presentation

Fishery impact on anadromous whiteﬁsh populations in River Tornio

1 2 2 ∗Erkki Jokikokko , Lari Veneranta , Jarno Jääskeläinen 1Luonnnonvarakeskus, Finland 2Luonnonvarakeskus, Finland Tagging of anadromous whitefish indicated that traditional dipnetfi shing can cause significant mortality on summer ascending whitefish population. Carlin and T-anchor tags were used to tag summer ascending whitefish at their spawning run in July-August in the lower part of River Tornionjoki in 1977, 2016 and 2017. The tag return rates in 1977 and 2016 were high, 19.8 and 19.0 %, but in 2017 only 7.5 %. Majority of the returned tags (>90%) came from dipnetfi shery in the river in July-September soon after tagging. Whitefish were also caught with gillnets in October 1977 and tagged with Carlin-tags. Their total return rate was 22%. Opposite to the summer taggings the recaptures of October tagged whitefish came mainly (>90%) from the sea in next years becausefi shing was not allowed in the river in late autumn except this broodfi sh gillnetting. Tag returns showed that thefi shing effort to summer ascending population differs from that of autumn whitefish. Dipnetting in the river has an essential role to the status of summer population whereasfi shing during feeding migration in the sea affects the late ascending populations. Therefore management of whitefish in River Tornio, a spawning population based approach is needed. Assesment, conservation & management Oral presentation

Genetic stock identiﬁcation of marine whiteﬁsh (Coregonus lavaretus) from a mixed stock catch reveals differences in growth and migration patterns among stocks

∗Tuomas Leinonen, Irma Kallio-Nyberg, Marja-Liisa Koljonen, Lari Veneranta, Erkki Jokikokko Natural Resources Institute Finland, Finland Fisheries where genetically and phenotypically distinctfi sh populations aggregate into mixed stocks during feeding migration present a challenge for sustainable management. For example, mixed stocks may include populations with different conservation status or differing productivity, meaning that each population requires a different harvest strategy. Harvesting is often size-selective, and may therefore also induce differential se- lection on populations with different in growth rates and migration patterns. We used a combination of DNA- microsatellite and gill raker count data to probabilistically assign individual European whitefish (Coregonus lavaretus) in mixed-stock sea catches from the Gulf of Bothnia into their source populations. We also quantified differences in migration patterns and growth rates among the identified populations of origin. The mixed-stock sea catches were taken at different parts of the Bothnian Bay, the Quark, and the Bothnian Sea at different times of year, and comprisedfi ve anadromous and two sea-spawning source populations. We found that despite the relatively low neutral genetic differentiation among most of the source populations, there were clear differences in migration patterns and growth rates among the source populations. Our results highlight the importance of considering both genetic and ecological differences the management of mixed stockfi sheries. Assesment, conservation & management Oral presentation

It’s a Trap! Using a new egg trap to sample coregonine eggs in Lake Ontario

∗Hannah Lachance, Cameron Davis, Brian Weidel USGS, USA Multiple partners have expressed their support for restoring coregonines in the Great Lakes. To inform coregonine restoration efforts it’s important to understand where coregonines spawn (i.e. which locations, depths, and substrates). In the past, research in Lake Ontario has focused on a few rocky, shallow shoals within Chaumont Bay with minimal work done outside of Chaumont Bay or at varying depths or substrates. Additionally, previous studies used egg mats and egg pumps which can over or underestimate egg depositions and are difﬁcult to deploy and process. Therefore, to obtain better estimates of egg deposition and to increase the number of traps we can deploy and process, we designed a metal ring trap modeled after the Horne’s trap. Both metal ring traps and egg mats were deployed at various depths, substrates and locations within and outside of Chaumont Bay. The metal ring traps were shown to be successful and comparable to egg mats. Additionally, coregonine eggs were found throughout Chaumont Bay and off of Horse Island, predominantly, but not exclusively, on shallow, rocky sites. Utilizing the metal ring trap can increase the number of traps deployed and processed in a given ﬁeld season, allowing us to expand our coreogonine spawning assessments. Assesment, conservation & management Oral presentation

Natural reproduction of anadromous whiteﬁsh (Coregonus lavaretus) in dammed and undammed rivers

1 2 3 ∗Lari Veneranta , Erkki Jokikokko , Pekka Jounela 1Natural Resources Institute Finland (Luke), Finland 2Natural Resources Institute Finland (Luke) / Research Scientist, Finland 3Natural Resources Institute Finland (Luke) / Senior Specialist, Finland We compared the level of natural reproduction of anadromous whitefish below the lowest dam in the rivers Kemijoki and Iijoki and in undammed river Tornionjoki. Newly hatched whitefish larvae were tagged with alizarin red and a dipnet catch sampling program was initiated immediately after stocking. The sampling covered the entire downstream migration period. Information on the total numbers of stocked alizarin tagged larvae and their number in dipnet catch and naturally reproduced larvae in dipnet catch was used to estimate the rivers’ natural reproduction by using a Petersen method and bootstrap aggregated MLP NN model. The average estimate of natural reproduction was 0.6 million larvae for the river Kemijoki, 0.4 million in the river Iijoki and up to 22 million in the river Tornionjoki. The predicted natural reproduction in the undammed river Tornionjoki was on average 40 to 60 times higher than the estimated values in the dammed rivers Kemijoki and Iijoki. The results show that in regulated rivers the natural reproduction of whitefish is minimal compared to natural rivers despite high number of broodfi sh and existing spawning areas, probably due to high variation in discharge after spawning and reduced surface area of spawning locations. Assesment, conservation & management Oral presentation

Population genetics of a resurging lake whiteﬁsh, Coregonus clupeaformis, population in the Detroit River

1 2 ∗Wendylee Stott , Edward Roseman 1Michigan State University, USA 2USGS-Great Lakes Science Center, USA Ecological restoration programs aim to create a self-sustaining and resilient system. Genetic variation is a prerequisite for evolutionary response to environmental changes, therefore it is important to monitor genetic diversity of restored populations. The Detroit River, connecting the Great Lakes Lake Huron and Lake Erie once supported a substantial lake whitefish (Coregonus clupeaformis)fi shery until the early 1900s, when habitat loss and degradation, pollution, and other factors contributed to the decline of thefi shery. The last reported landing of lake whitefish was 1925. In the early 1970s a series of efforts were initiated to improve water and habitat quality, and in December 2005 a spawning male lake whitefish and viable eggs were collected; thefi rst documented evidence of spawning since 1916. Researchers have continued to track the development of the lake whitefish population in the Detroit River by sampling adults, larvae, and eggs. Microsatellite DNA data have been used determine the relative contributions of Lake Erie and Lake Huron to the resurging population and track changes in diversity. Lake Erie contributed more to the resurging population than Lake Huron. Estimates of genetic diversity have changed over time but are still lower in the Detroit River population than in source populations. Assesment, conservation & management Oral presentation

Sodium and manganese sulphate toxicity to early life stages of European whiteﬁsh

∗Anna Karjalainen, Mikko Mäkinen, Juha Karjalainen University of Jyväskylä, Finland Sulphate occurs naturally in the aquatic environment but its elevated levels are toxic to aquatic life in freshwater environments. Sulphate levels can be elevated by discharges from multi-metal mining, chemical industry, pulp production, agricultural runoff, power plants and municipal wastewater treatment plants. Adultfi sh seem to tolerate high sulphate concentrations in their environments but early developmental stages can be much more susceptible. Many whitefish stocks have declined or are endangered due to deterioration of their breeding areas and weakening water quality. In Finland, there are currently no water quality criteria for sulphate designed to be protective of aquatic life. We will present the toxicity of two compounds, sodium (Na2SO4) and manganese (MnSO4) sulphate, to European whitefish (Coregonus lavaretus) embryonic development from fertilization of eggs to hatching and after hatching to 3 to 5-day-old yolk sac larvae in humic freshwater. Thefi nished 160-d exposure to MnSO4 decreased whitefish embryonic survival, and the lethal concentrations (LC50-values) ranged from 42 to 85 mg/L depending on the parentfi sh. Exposure to Na2SO4 underway have reduced the fertilization rate and early survival of whitefish embryos only in the highest (2 960 mg/L) Na2SO4 concentration. Assesment, conservation & management Oral presentation

St. Marys River Rapids Area Provides Valuable Habitat for Coregonine Reproduction

1 2 3 2 2 ∗Robin DeBruyne , Edward Roseman , Christopher Olds , Wendylee Stott , Stacey Ireland , Eric Adams 2, Jason Gostiaux 1, Jason Fischer 2 1University of Toledo, USA 2USGS Great Lakes Science Center, USA 3USFWS Alpena Fish and Wildlife Conservation Office, USA The St. Marys River is the Great Lakes connecting channel between lakes Superior and Huron with a variety of habitats present. Waterfl ow is regulated through navigational locks and compensating gates directly upstream of the area known as the St. Marys Rapids. This area is considered an importantfi sh spawning and nursery area, although no research has assessedfi sh use or production. During 2018 and 2019, active and passive egg and larval sampling was conducted to measure the timing and abundance of eggs and larvae upstream and downstream of the rapids. Coregonine eggs were found at 3 sites near the rapids in fall of 2018. Drifting Coregonine eggs and larvae were collected during weekly sampling during May and June in both years. Most fish were collected downstream of the rapids as mesolarvae, although some sac-fry stage were collected. None were found above the rapids in 2018 but were collected upstream in 2019. Visual identification of specimens indicates presence of lake whitefish and likely cisco, with genetic confirmation of identities pending. These results suggest that the St. Marys River Rapids area is an important source of Corogeonine production and transport. Assesment, conservation & management Oral presentation

The Future of Coregonine Restoration in the Laurentian Great Lakes

1 1 1 1 2 2 ∗Kurt Newman , Russell Strach , David Bunnell , Devin Murray , John Dettmers , Andrew Muir , Charles Bronte 3, Mike Millard 3 1US Geological Survey, USA 2Great Lakes Fishery Commission, USA 3US Fish and Wildlife Service, USA Restoring native Coregonines is a top priority forfi sheries managers in the Laurentian Great Lakes. Core- gonines, once abundant across the lakes, provided an important prey base and robust commercialfi sheries. Many of the historic populations of these species are significantly reduced in abundance or have gone extinct. Restoration of Coregonine populations could in turn restore ecosystem function, reestablish lost resilience in the lakes, and sustain economically importantfi sheries. Initial efforts at restoration were fractured and lacked common objectives. Recently, the USGS Great Lakes Science Center led an initiative to align United States Department of Interior agencies in their Coregonine restoration efforts. The initiative is focused on ensuring efforts are grounded in the science and principles of restoration ecology and conservation biology rather than relying simply on stocking as a restoration tool. Basin-wide efforts led to the formulation of a conceptual framework to adaptively manage the long-term restoration of Coregonines. The adaptive framework outlines steps for planning and conducting science and implementing appropriate management options towards restoring the species. The framework has now gained bi-national and tribal support and will guide the future direction of science in support of management decisions to restore Coregonines to the Great Lakes. Assesment, conservation & management Oral presentation

The genetic structure of anadromous and sea-spawning European whiteﬁsh stocks and the genetic origin of commercial catches in the Baltic Sea

1 1 1 1 ∗Marja-Liisa Koljonen , Lari Veneranta , Irma Kallio-Nyberg , Erkki Jokikokko , Jarmo Koskiniemi 2, Tuomas E Leinonen 2 1Natural Resources Institute, Finland 2University of Helsinki, Finland Genetic identification of stocks and information on their contribution to commercial catches are the prereq- uisites for stock levelfi shery management. We analyzed diversity levels and genetic differentiation among anadromous and sea-spawning European whitefish (Coregonus lavaretus) stocks in the Bothnian Bay, in the northern Baltic Sea. The current whitefish stocks were identified based on 2211 samples from 27 known whitefish rivers or marine reproduction areas. To estimate the proportion of different stocks infi shery, 1187 commercial catchfi sh were sampled in 2008-2014 fromfi ve coastal areas. In total, the data included genetic variation of 16 DNA-microsatellite loci and the gill raker number distribution in the 27 stocks and individual catchfi sh. Clear, statistically significant genetic differences were found among geographically distant whitefish stocks and between ecotypes. As a result of simulation tests 14 genetically similar stock groups could be defined, and they could be identified in the catches. The stock composition of commercial whitefish catches varied markedly among areas from north to south. This work forms the base for defining management units, for planning whitefish offspring releases, and for the utilization of genetic stock composition analysis of catches. Assesment, conservation & management Poster session

Assessment of Lake Huron coregonines through integrated acoustic and trawl surveys

1 1 1 2 1 ∗Timothy O’Brien , Dave Warner , Steve Farha , Chris Olds , Peter Esselman 1USGS Great Lakes Science Center, USA 2US Fish and Wildlife Service, USA Lake Huron is the fourth largest lake in the world by area, covering nearly 60,000 square kilometers of On- tario, Canada, and the state of Michigan, USA. Historically, Lake Huron had seven endemic forms of ciscoes occupying diverse habitats. Through the effects of overexploitation, invasive species, and habitat modification, most of this coregonine diversity was lost and only the bloater Coregonus hoyi and cisco Coregonus artedi remain. Accurate estimates of the distribution and biomass of these species are necessary for conservation purposes and for understanding their importance to the food web. Acoustic-trawl surveys have proved to be an effective method for surveying large bodies of water because of the ability to sample large water volumes with a large range offi sh sizes. Annual hydroacoustic-trawl surveys were conducted during 2004-2019 to estimate biomass of pelagic preyfi sh communities during late summer. Bloater averaged nearly 70% of annual pelagic fish biomass during the 16-year period and were widespread in deeper areas of the lake. Cisco were relatively rare and restricted to northern waters, but their abundance increased over the time series. This paper focuses on the value of acoustic surveys for measuring abundance and understanding the ecology of coregonines in large systems. Assesment, conservation & management Poster session

Assessment of the state of spawning grounds of sea-spawning whiteﬁsh at Hiiumaa, Baltic Sea: implications for local management and conservation decisions

∗Lauri Saks, Aare Verliin, Kristi Källo, Lagle Matetski, Imre Taal, Redik Eschbaum Estonian Marine Institute, University of Tartu, Estonia The spawning grounds of sea-spawning whitefish (Coregonus lavaretus) have been protected with temporal fishing restrictions for several decades. However, the local reproduction success is sporadic. To assess the efficiency of the spawning stock protection measures precise spawning localities and assessment of the state of spawning grounds were carried out. The results indicated that currently functional spawning sites have shifted and protected spawning localities have degraded below functional quality. Thus, areas with temporalfi shing restrictions have to be reallocated to corresponding spawning sites to enhance conservation measures for this sea-spawning whitefish population. Assesment, conservation & management Poster session

Catch size-at-age of the anadromous whiteﬁsh in the northern Baltic under different mesh size limits in gill nets

∗Irma Kallio-Nyberg, Lari Veneranta, Erkki Jokikokko LUKE, Finland Length-at-age of anadromous European whitefish (Coregonus lavaretus) was studied in the Gulf of Bothnia (GoB) from catch before and after gillnet mesh size change that was set to protect whitefish from highfi shing pressure. In 2013 the lowest allowed mesh size (from knot to knot) in the gillnetfi shing of anadromous whitefish was raised to 43 mm in the GoB from previous 40 mm. As an exception, in the central GoB the minimum mesh size was kept as 40 mm. Commercial gillnet catch samples from years 1998-2017 and spawning population sample from the river Kemijoki was analyzed. Majority of anadromous whitefish are stocked in the rivers located to the northern GoB. These stocks migrate to the southern GoB for feeding and return as maturefi sh to the north. After mesh size changes the length of the whitefish caught in southern GoB increased at ages 3-5, but this was not observed on the northern catches. Still, at the ages 5 and 6 the catch length decreased in the north. Temperature regulates the growth of whitefish, but to increase catch size, a uniform mesh size regulation is needed in the GoB. Assesment, conservation & management Poster session

Monitoring Coregonid catches in three lakes for 35 years shows effects of management, reoligotrophication and climate change.

∗Arthur Kirchhofer, Martina Breitenstein WFN – Wasser Fisch Natur AG, Switzerland The sustainable exploitation offi sh stocks is a primary concern offi sheries regulations in Switzerland. There- fore since 1984 the Coregonid catch of commercialfi sheries is surveyed monthly in three lakes with decreasing trophic state – L.Biel, L.Thun and L.Brienz. Time-series analysis of different parameters over 35 years document the evolution of catch-composition in length, weight and condition, age composition and growth. Changes in mesh size andfi shing intensity are revealed, as well as the effects of reoligotrophication. The latter seriously threatens the commercialfi shery in at least one lake and undermines the profitability of this profession in the other ones. Furtheron strong decreases of growth can be observed in the years with very high summer temperatures. Pos- sible reasons for such an effect of climate change are discussed. Assesment, conservation & management Poster session

Monitoring European whiteﬁsh stomach content is a vital tool for biomonitoring of a rare crustacean (Lepidurus arcticus: Notostraca, Branhiopda) in a large lake

1 2 3 4 3 ∗Hanna-Kaisa Lakka , Antti Leppänen , Heikki Mykrä , Markku Vaajala , Sari Raineva , Terhi Lensu 5, Erno Salonen 4 1Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland 2Eurofins Ahma Oy, Jyväskylä, Finland 3Finnish Environment Institute (Syke), Oulu, Finland 4Natural Resources Institute Finland (Luke), Inari, Finland 5Eurofins Ahma Oy, Jyväskylä, Finland, Finland Detection of rare species from aquatic ecosystems requires numerous samples and sampling events. The Arc- tic tadpole shrimp (Lepidurus arcticus) is a rare and endangered crustacean species in Finland. This large- sized Branchiopoda is important prey for brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) in Fennoscandia, but it has been found only in a few lakes in Finland. In July 2018, three bays in the southern end of Lake Inarijärvi in northern Finland were selected as monitoring stations to examine the changes in the catch and the feeding pattern of whitefish (Coregonus lavaretus). Fish were caught with seine net and stomachs were obtained from 180 individuals. Waterfl eas (Cladocera sp.) were the most abundant prey items, but benthic invertebrates were also common, particularly in the diet of largerfi sh. One L. arcticus was found. Inarijärvi is the only lake worldwide where C. lavaretus has been observed to feed on L. arcticus. Fish stomach content analysis can provide valuable information of occurrence of endangered crustacean species. It would be important to repeat these studies in the future and also conduct them in other subarctic or alpine lakes. Key words: Arctic tadpole shrimp, conservation, Coregonus lavaretus, stomach content analysis Assesment, conservation & management Poster session

New approaches for the Coregonid management in German coastal waters of the Baltic Sea

∗Dominik Bernolle, Gerd-Michael Arndt Mecklenburg-Vorpommern Research Centre for Agriculture and Fisheries, Germany C. maraena migrates from autumn to spring into the inner coastal waters of the southern Baltic Sea to reach its spawning grounds. During this migration localfi sheries are targeting C. maraena using gillnets and fyke nets. The rest of the year the species seems to be widely distributed in the outer coastal waters. A long and continuous decline of the population between the 1970s and 80s resulted 1995 in an all-time low of 3 t per year. Since 1994 various measures have been taken to halt the decline, including annual stocking. These conservation effort have not resulted in a full recovery of the stock however. The goal of this project is to identify parameters and conditions influencing the C. maraena population in the study area. This is achieved by using various methods to identify the utilized spawning grounds, and analysing reproduction processes. By using combined information a well-adapted management plan can be developed, enabling a sustainable use of the population by the localfi shing industry. Assesment, conservation & management Poster session

Results of the introduction of the European vendace Coregonus albula into Karelia’s water bodies

∗Sterligova Olga, Ilmast Nikolay Institute of Biology KRC RAS, Russia The results of the introduction of the various forms of the European vendace Coregonus albula into the water bodies of Karelia, Russia, were analyzed. The vendace was shown to have naturalized in almost all the lakes into which it was released. Its biological parameters under new living conditions (age composition, linear-weight growth and fecundity) were studied. It has been shown that in the lakes studied the vendace formed large self- reproducing populations and became a majorfi shing item. As the vendace has settled, the structure of trophic relationships in the lakes has changed. There are now two matter and energyfl ows: benthos–benthos-eating fish – predatoryfi sh and plankton–vendace–predatoryfi sh. It has been shown that as a result of the premediated introduction of vendace, thefi sh population of the lakes now comprises a valuable species which contributes to the more complete use of food resources. The studies were funded by RFBR Project 18-04-00163a. Assesment, conservation & management Poster session

Spawning ground identiﬁcation by sub-bottom proﬁling and ROV

∗Josef Hrabowski Mecklenburg-Vorpommern Research Centre for Agriculture and Fisheries, Germany With a decreasing Coregonus populations in north German lakes, management plans that protect the remaining stocks and introduce Coregonids to new lakes are badly needed. One of the largest obstacles to developing such plans is the lack of knowledge needed spawning ground conditions for the Coregonus species in the area. In this project potential spawning ground are identified using sub-bottom profilers, lake morphology and general Coregonus spawning behaviour. Once potential spawning grounds are identified the actual habitat usage is assessed by indirect methods, such as gillnet surveys and by direct observation, using a Remotely operated vehicle. While the direct proof of spawning activity has not yet been found for any area, the evidence of indirect methods made it possible to move some areas from the category of potential spawning ground to likely spawning ground. With this knowledge the catchability of mature Coregonus individuals, with the purpose of restocking programs, has already been drastically increased. Using either mounting indirect evidence, or direct observation, we will be able to identify the kind of habitat used by Coregonus species in north Germany and with this knowledge protect those areas and identify lakes with the capability of sustaining a breeding Coregonus population for reintroduction. Assesment, conservation & management Poster session

The contribution of commercialﬁ shers’ catch and effort statistics to understanding Finnish inland vendaceﬁ sheries

1 1 1 2 ∗Tapio Keskinen , Mika Rahikainen , Timo Ruokonen , Timo J. Marjomäki 1Natural Resource Institute Finland, Finland 2University of Jyväskylä, Finland The New Fishing Act was implemented in Finland in 2016. It specifies, in concert with the Act on food and natural resource statistics, that the commercialfi shers in inland waters have to report their monthlyfi shing effort and catch to Natural Resources Institute (Luke) once a year. Coupling catch data withfi shing technology and effort data provides key knowledge for evaluations on the exploitation of inland waterfi sh resource on spatial and temporal scales that are relevant forfi sh stock assessment andfi sheries management. Vendace (Coregonus albula L.) is the most important species in inland commercialfi sheries in terms of quantity and value. It accounts for almost half of the commercial catch volume and over 40 % of value. Proportionally, recreational landings of vendace are typically marginal in commercially exploited lakes. In this study, we evaluate the applicability of the available catch and effort data originating from commercialfi shery forfi sh stock assessment andfi sheries management in different spatial scales. We present statistics onfi shing effort and vendace catch in Finland in years 2016–2018. Further, we evaluate the suitability offi shing effort, vendace catch and CPUE data for making management decisions for targeted vendacefi shery in lake level.