Interim Report of the Stock Identification Methods Working Group (SIMWG)

ICES SIMWG REPORT 2015

SCICOM STEERING GROUP ON ECOSYSTEM PRESSURES AND IMPACTS

ICES CM 2015/SSGEPI:13

REF. ACOM, SCICOM

Interim Report of the Stock Identification Methods Working Group (SIMWG)

10-12 June 2015

Portland, Maine, USA

International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer

H. C. Andersens Boulevard 44–46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk [email protected]

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ICES. 2015. Interim Report of the Stock Identification Methods Working Group (SIMWG), 10–12 June 2015, Portland, Maine, USA. ICES CM 2015/SSGEPI:13. 67 pp.

For permission to reproduce material from this publication, please apply to the Gen- eral Secretary.

The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council.

ICES SIMWG REPORT 2015 | i

Contents

Executive summary ...... 3

1 Administrative details ...... 4

2 Terms of Reference ...... 4

3 Summary of Work plan ...... 4

4 List of Outcomes and Achievements of the WG in this delivery period ...... 4

5 Progress report on ToRs and workplan ...... 5 5.1 ToR a) Review recent advances in stock identification methods ...... 5 5.1.1 Genetic Analysis ...... 5 5.1.2 Life history parameters ...... 6 5.1.3 Body Morphometrics ...... 7 5.1.4 Tagging (conventional, acoustic, satellite)...... 7 5.1.5 Growth marks in calcified structures ...... 9 5.1.6 Otolith Shape ...... 9 5.1.7 Otolith Chemistry ...... 10 5.1.8 Parasites ...... 11 5.1.9 Early life stages ...... 12 5.1.10 Simulation approaches ...... 13 5.1.11 Interdisciplinary analysis ...... 14 5.2 ToR b) Build a reference database with updated information on known biological stocks for species of ICES interest ...... 16 5.2.1 Summary of workplan and progress on database...... 16 5.2.2 Technical reviews ...... 17 5.3 ToR c) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment...... 17

6 References ...... 21

7 Revisions to the work plan and justification ...... 28

8 Next meetings ...... 28

Annex 1: List of participants...... 29

Annex 2: Recommendations ...... 30

Annex 3: Agenda ...... 31

Annex 4: ToR B – Tables ...... 33

Annex 5: Evaluation of Greater Silver Smelt Stock Identity in ICES Subareas I, II, IV, VI, VII, VIII, IX, X, XII and XIV and Divisions IIIa and Vb ...... 38

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Annex 6: Evaluation of Plaice Stock Identity in ICES sub-area IIIa and Adjacent Areas ...... 42

Annex 7: Evaluation of Haddock Stock Identity in ICES Subareas IV and VIa (North Sea and West of Scotland) ...... 48

Annex 8: Evaluation of European Anchovy Stock Identity in ICES Division IXa ...... 56

Annex 9: Evaluation of Megrim Stock Identity in ICES Subareas VIIIc and IXa ...... 62

ICES SIMWG REPORT 2015 | 3

Executive summary

The Stock Identification Methods Working Group (SIMWG) held a meeting at the Gulf of Maine Research Institute in Portland, Maine (USA) on 10–12 June 2015. The work plan for SIMWG in 2015 comprised three Terms of Reference (ToR), most of which, being multiannual, will require additional work over the coming years: a ) Review recent advances in stock identification methods; b ) Build a reference database with updated information on known biological stocks for species of ICES interest; (1) Technical reviews and expert opinions on matters of stock identification, as requested by specific Working Groups and SCICOM; c ) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment. ToR a) is a key, ongoing task of SIMWG in which we provide a comprehensive update on recent applications of stock identification techniques to ICES species of interest, summarize new approaches in stock identification, and novel combinations of existing applications. ToR b) is a multi-annual ToR in which SIMWG is taking steps to build a reference database consisting of SIMWG reviews of issues of stock identity for ICES species. Under this ToR we have also addressed specific requests by ICES working groups for technical advice on issues of stock identity. Specifically, we provided advice on the following species: 1) haddock Melanogrammus aeglefinus (as requested by WKHAD), 2) megrim Lepidorhom- bus whiffiagonis (as requested by WGBIE), and 3) anchovy Engraulis encrasicolus (as requested by WGHANSA). Two additional species were reviewed by correspondence over the past year: 1) greater silver smelt Argentina silus (as requested by ADGDEEP), and 2) plaice Pleuronectes platessa (as requested by WKPLE). ToR c) is a multi-annual ToR that is focused on tracking developments in the application of mixed stock analysis and the integration of this information into assessment and management.

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1 Administrative details

Name of the Working Group Stock Identification Methods Working Group (SIMWG) Year of Appointment: 2014 Reporting year within current cycle: 2 Chair(s) Lisa Kerr, USA Meeting venue Portland, Maine USA Meeting dates 10–12 June 2015

2 Terms of Reference

SIMWGs multiannual ToRs are as follows: a ) Review recent advances in stock identification methods; b ) Build a reference database with updated information on known biological stocks for species of ICES interest; (1) Technical reviews and expert opinions on matters of stock identification, as requested by specific Working Groups and SCICOM; c ) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment.

3 Summary of Work plan

Year 1 Organise a physical meeting for SIMWG for summer 2015, trying to identify a period of the year that would allow best coordination with benchmarking processes. Establish working agreement with ICES web designers for delivery of ToR b. Year 2 Focus primarily on ToR b and assess personnel commitment and feasibility of ToR c. Year 3 Complete the first version of ToR c.

4 List of Outcomes and Achievements of the WG in this delivery period

• SIMWG organized and held a physical meeting in Portland, Maine, 10–12 June 2015

• SIMWG provided an update on recent applications of stock identification methods to ICES species and on recent advances in stock identification methods.

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• SIMWG developed summary materials of past SIMWG reviews on issues of stock identity for ICES species (1998-2014). This information will be used to build an online reference database.

• SIMWG provided expert advice on the following species: 1) Haddock Melanogrammus aeglefinus (as requested by WKHAD) 2) Megrim Lepidorhombus whiffiagonis (as requested by WGBIE) 3) Anchovy Engraulis encrasicolus (as requested by WGHANSA) 4) Greater silver smelt Argentina silus (as requested by ADGDEEP) 5) Plaice Pleuronectes platessa (as requested by WKPLE) • SIMWG provides a review of advances in mixed stock analysis focusing on the key aspect of baselines.

5 Progress report on ToRs and workplan

5.1 ToR a) Review recent advances in stock identification methods In the last year, there have been several notable advances in stock identification methods and a proliferation of applications, with many results relevant to ICES science and advice. Here, we summarize advances and results accounting for research in genetics, life history parameters, morphometrics, tagging, otoliths, early life history stages, parasites, simulation modeling, and interdisciplinary approaches.

5.1.1 Genetic Analysis New genomic approaches to marker discovery have been widely credited with catalyz- ing a shift from traditional low-coverage markers, such as microsatellites, to genome- wide polymorphisms, such as SNPs. Notwithstanding these advances in methodology, the lower costs associated with microsatellite applications will likely guarantee the persistence of these markers in the tool-box of stock identification practitioners (Mariani & Bekkevold 2013). Here we conducted the same bibliographic analysis performed in Mari- ani & Bekkevold (2013), to cover the most recent five years of scientific output (Figure 1), which shows that microsatellites continue to be the most widely used method, and that the relative importance of these classes of markers appears stable over the short-term.

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120 microsatellites

SNPs 100

0 2011 2012 2013 2014 2015

Figure 1. Scientific publishing trend since 2011, comparing outputs of studies using microsatellites (white bars) and SNPs (black bars), as listed in the ISI Thompson-Reuters Web-of-Science. The search criteria were: “fish* AND gene* AND (population OR stock) AND ‘molecular marker*’,” where ‘molecular marker*’ means “Microsatellite*” or “SNP*”. Only papers in the following disciplinary areas were considered: ‘Fisheries’, ‘Ecology’, ‘Environmental Sciences’, ‘Oceanography’, ‘Marine Biology’, ‘Limnology’.

As the operational costs for SNP discovery and genotyping continue to decrease, SIMWG will continue to produce these projections and similar analyses, in order to monitor the short-term changes in molecular marker usage in fisheries science. Additionally, there were a few new applications of genetic methods over the past year that are of direct relevance to ICES advice. Gonzalez et al. (2015) investigated spatial structuring in ling (Molva molva), identifying two genetically distinct groups: 1) a western ‘Iceland-to-Rockall’ unit and 2) an eastern unit distributed between Faroe and Norway. This new finding could have direct implications for assessment and management. Of similar novelty was the finding that lumpfish (Cyclopterus lumpus) was also found to have two genetically distinct groups in the North Atlantic (1) between Maine and Greenland and 2) between Iceland and Norway), plus a separate unit in the Baltic (Pampoulie et al. 2014). Shum et al. (2015) corroborated the genetic separation between deep-sea oceanic redfish (S. mentella) in the Irminger Sea and western Faroes and the more widespread ‘shallow’ population, distributed across most of the distribution range of the species. This study utilized temporally distributed samples and multiple markers on the same fish. Bekkevold et al. (2015) applied SNPs to assign individual Atlantic herring to their regional origin in the Northeast Atlantic. The study reported evidence that herring from the Baltic Sea contribute to catches in the North Sea, and that western Baltic feeding aggregations are primarily comprised of herring from the western Baltic with some contributions from the Eastern Baltic.

5.1.2 Life history parameters An exciting, emerging trend in the investigation of stock structure is the application of newer statistical methods to spatially-explicit life history data. For example, Winton et al. (2014) applied generalized additive models (GAMs) to plot variation in maturity sched- ules of winter flounder (Pseudopleuronectes americanus) in northeastern U.S. waters, an area with three fishery stocks. In terms of model fitting, GAMs perform better than traditional linear models (GLMs) using aggregated data, such as reported by McBride et al. (2013). In another example of novel approaches, Midway et al. (2015) applied a hierar-

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chical Bayesian framework to model size-at-age data of southern flounder, Paralichthys lethostigma. They reported considerable variation in growth rates between, and within, the Atlantic Ocean and Gulf of Mexico basins surrounding the southeastern U.S. In relation to recent genetic and otolith shape analyses on southern flounder, describing only between-basin differences (e.g., Midway et al. 2014), these growth differences are presumably ecophenotypic, but were persistent over time, and as vital rates, they may be relevant to state-managed fisheries plans.

Life history traits were also used as the basis to investigate or explain stock structure of ICES species, in some cases this work built of previous work using other methods. A recent study of European hake, Merluccius merluccius, revealed strong genetic differentiation between Atlantic and Mediterranean basins as well as finer-scale population structure within these basins (Milano et al. 2014). Working within this context, Vittori (2015) compared population structure between the western and eastern shores of Sardin- ia. In terms of life history, length differences were known between these coasts, but closer examination suggested that this arose from more complex spawning pattern on one coast, and not from fundamental differences in growth. Modest coastal differences in fish morphometrics were observed, but no differences between parasite assemblages were observed, leading Vittori to conclude that the hake around Sardinia was a single stock unit. Petersen (2014) examined stock structure of Atlantic cod, Gadus morhua, around the Faroe Islands, where it was well known that cod on the Faroe Bank had higher growth than the cod residing on the colder Faroe Plateau. Petersen found additional life history differences (spawning times, egg size and numbers per batch), and both microsatellite and single nucleotide polymorphism demonstrated genetic differences between these submarine regions of the Faroe Islands.

5.1.3 Body Morphometrics Classic body morphometric approaches continue to shed light on population structure of species in the ICES area. In the past year, this technique has been applied in combination with other techniques and is reported on in the Interdisciplinary Analysis section.

5.1.4 Tagging (conventional, acoustic, satellite) Tagging remains a common approach for studying the distribution, behaviour, and movements of marine fish for application to stock identification. Several recent studies have used newly developed tagging technologies and approaches to study ICES species of interest and species from other regions. These studies have provided new insights into fish migrations and developed advanced analytical methods. While earlier studies relied on conventional tagging to study fish movements, recent studies have increasingly focused on using electronic tags given continued technological advancements with respect to tag design and capabilities. Acoustic telemetry is one type of electronic tag that has become increasingly popular among researchers and the resulting data have provided new insights into fish population dynamics. For example, acoustic telemetry was used to document spawning activity of winter flounder (Pseudopleuronectes americanus) in coastal waters of the Gulf of Maine, a species previously thought to be obligate estuarine spawners (DeCelles and Cadrin, 2010; Fairchild et al., 2013). Acoustic telemetry was also used to study the pre- and post-

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spawning behaviour of Atlantic herring (Clupea harengus) within a coastal ecosystem off Norway (Langård et al., 2015). Acoustic telemetry was also recently used to determine the migratory behaviour of Atlantic cod (Gadus morhua) in relation to the boundaries of marine protected areas in Gilbert Bay, Labrador (Morris et al., 2014). Technological advances have also increased the applicability of acoustic telemetry, thus presenting new opportunities for studying fish movements. For example, Deng et al. (2015) developed the first acoustic transmitter that can be implanted by injection rather than surgery, enabling tagging of smaller fish than possible with previous tags. They used their newly developed tag to study river passage of juvenile salmon. Also, attach- ment of acoustic receivers to underwater gliders can increase the area that can be monitored for tagged fish. For example, Oliver et al. (2013) used an acoustic receiver strapped to an AUV to monitor the movements of Atlantic sturgeon off the east of the USA, while simultaneously collecting oceanographic data to investigate habitat preferences. New technologies and analytical approaches have also enabled researchers to investigate predation (e.g. Gibson et al., 2015) and species interactions (e.g. Lidgard et al., 2014) using acoustic telemetry data. Archival data storage tags (DSTs) which record environmental data (e.g. temperature, depth, salinity) while fish are at liberty have also commonly been used to study fish behaviour and movements. Data from recovered DSTs have been used in multiple geolocation studies which reconstructed migration paths of cod using environmental data (see Neuenfeldt et al., 2013 for review). Geolocation is advantageous because it provides insights into fish movements beyond the release and recapture positions, which are typical- ly all that are known with conventional tagging, and it enables determinations of positions within a broader area than possible with acoustic telemetry receivers. For example, Le Bris et al. (2013a) used DSTs to study cod movements throughout the Gulf of St Lawrence and documented evidence of partial migration behaviour with a combination of resident and migratory individuals. Similarly, Neat et al. (2014) used data from DSTs and geolocation analyses to document a range of behaviours of cod around the British Isles, including migration, site fidelity, and limited home ranging. They used their tagging data to conclude that cod around the British Isles are comprised of at least one more distinct population unit than is currently recognized for management purposes. Additionally, tagging studies are increasingly utilizing multiple tagging technologies to compensate for the respective weaknesses of each type of tag (e.g. financial cost, data resolution). For example, Sólmundsson et al. (2015) used conventional tagging and DST data to study the home ranges and spatial segregation of cod spawning components off Iceland. They found strong evidence of spatial structure within the cod population off Iceland, including within-population diversity, emphasizing the need for considering this population structure in fishery management plans. Le Bris et al. (2013b) combined conventional tagging and DST data to study cod movements in the Gulf of St Lawrence with respect to a spawning closure to evaluate the efficacy of this closure with respect to protecting spawning cod. Kneebone et al. (2014) used data from conventional tags, acoustic telemetry, and pop-up satellite archival tags (light-based geolocation) to study the movement patterns of juvenile sand tiger sharks (Carcharias taurus) along the east coast of the USA. Combining data from all three tag types can be critical to describing both the fine- and broad-scale movements of fish species.

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Efforts are ongoing to incorporate tagging data into stock assessment models, including data from both conventional (Goethel et al., 2015) and electronic tags (Sippel et al., 2015). Such advancements will increase the likelihood for tagging data to be considered in the fishery management processes. The development of these tag-integrated models will likely lead to an increase in tagging studies to support the data needs of these models, thereby also increasing the amount of movement data available for investigating population structure.

5.1.5 Growth marks in calcified structures Otolith structural analysis continues to be used in stock identification research world- wide and ongoing work applying this technique was recently reported on at the 5th In- ternational Otolith Symposium (20–24 October 2014; see the book of abstracts at http://www.ices.dk/news-and-events/Documents/Symposia/Otolith/ IOS2014% 20Book%20of%20Abstracts.pdf for full details). Highlights from the meeting that are directly relevant to stock identity of ICES managed species are reported on below. We also describe methodological advancements in the field. Although these are not papers explicitly focused on stock discrimination, they describe techniques/methods that may be used in the future for stock identification purposes. In an abstract for the 2014 Otolith Symposium, Nava et al. described progress on a potential advancement in the field. The authors are developing a new tool designed to add ef- ficiency to the task of counting and measuring otolith growth increments through automation using computer algorithms. When completed, the software will be made available freely to the scientific community in the open access mode. This type of approach has been pursued before without broad acceptance. The focus of the application is on age estimation, but the ability to quickly and affordably measure growth increments could increase the application of this technique for the purpose of stock identity. In an abstract by Rey (October, 2014), the author described the applications of a plastic inclusion technique designed to enhance daily growth increment observation. The method involves filling the otoliths´ interstitial spaces with polymethyl metacrilate before the process of embedding in resin. The method results in structural reinforcement of the otolith which enables thinner slices that are more resilient than those obtained from the standard process. Although adding additional processing time, this methodological advance may ultimately improve resolution of daily growth increments. Moore et al. (October, 2014) described progress on application of otolith shape and microstructure to stock delineation of sprat in the Celtic Sea Ecoregion. In this study, the widths of daily increments within the larval region of the otolith were used to determine if fish collected from the two key fishing areas in the north and south of the region (ICES Div. VIa and VIIj) had distinct larval growth histories.

5.1.6 Otolith Shape New studies using otolith shape analysis for stock identification dealt with four pelagic species and two flatfish species in the North Atlantic. Bacha et al. (2014) and Jemaa et al. (2015b) investigated otolith outlines of European anchovy (Engraulis encrasicolus) across their distributional range along the Northeast Atlantic shelf (southern North Sea to Iberi- an coast) down to Mauritania and in the Mediterranean, utilizing Elliptic Fourier Analy-

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sis (EFA) and univariate morphometric descriptors. The study of Bacha et al. (2014) focused on the Algerian and Moroccan (Mediterranean and Atlantic) coast, as well as the Gulf of Cadiz. They found a clear distinction between Alboran, northeast Algerian and Atlantic areas. Jemaa et al. (2015b) used an expanded data set, covering the southern North Sea and English Channel, the Gulf of Cadiz, Morocco, Mauritania and western and eastern Mediterranean. With clearly distinct patterns, four regional groups were separated: a northern and a southern cluster in the Atlantic, a group of areas in the Gulf of Ca- diz, off Morocco and Algeria, and a cluster of Mediterranean sampling sites off Turkey, Greece, France and eastern Spain. Using the same methods, Jemaa et al. (2015a) looked at sardine (Sardina pilchardus) from the French Atlantic coast to Morocco, and in the Mediterranean. Interestingly, fish from a sample in the Eastern Channel (ICES Div. VIId) appear separate (in a cluster with Medi- terranean areas) from the Bay of Biscay and from fish sampled off the Portuguese coast. Samples from the Gulf of Cadiz, however, clustered with fish from Morocco and Algeria. A third group of samples was identified in the eastern Mediterranean and the Gulf of Lion/Catalan Sea. Further north, Libungan et al. (2015) tested differences between herring (Clupea harengus) from Iceland, Faroe Islands, Norway, and West of the British Isles, with an outgroup from eastern Canada. The area west of Scotland and Ireland separated well from the other areas, and a clear distinction could be detected between Icelandic summer spawners and Norwegian spring spawners. They used Wavelet analysis in an R pro- gramme package environment, which is also presented in a recent methodology paper (Libungan and Pálsson 2015). Using improved outline analysis techniques for complex contours, Harbitz and Albert (2015) reported on moderate separation between Greenland and Northeast Arctic (Bar- ents Sea) for Greenland halibut (Reinhardtius hippoglossoides). Midway et al. (2014) studied otolith shapes (EFA and univariate descriptors) of southern flounder (Paralichthys lethostigma) and found high classification success on a basin level, separating fish from areas west (Gulf of Mexico) and east of Florida (Georgia, South and North Carolina). Markedly lower classification between States and between finer-scale regions within North Carolina, however, suggested mixing of populations within basins.

5.1.7 Otolith Chemistry In November 2014, ICES sponsored the 5th International Otolith Symposium in Mallorca Spain (http://www.ices.dk/news-and-events/symposia/otolith/Pages/default.aspx), which attracted 329 registrants and 87 students from 45 countries. Symposium themes focused on otoliths as indicators of the (1) environment; (2) community; (3) population; and (4) individual. Population-oriented applications dominated the program, many of which employed otolith chemistry approaches. A themed session with the ICES Journal of Ma- rine Science to be published in 2015 will feature eight articles, half of which are otolith chemistry applications. This set includes a population mixing study: otolith 87Sr/86Sr was analyzed for anadromous Bering Sea cisco Coregonus laurettae by Padilla et al. (in press) to evaluate the relative contribution of three Alaskan river systems to a sample drawn from the coastal fishery. Interestingly the commercial sample was dominated (>97%) by a single system (the Yukon River). The other three applications were more focused on methods development. For NE Pacific albacore Thunnus alalunga, Wells et al. (in press) observed high discrimination above and below 40 °N using otolith stable isotopes δ13C

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and δ18O in concert with Ba:Ca, Mg:Ca, and Mn:Ca, but classification was not stable between years. Arrival into NE Pacific waters by western Pacific juvenile Pacific bluefin tuna Thunnus orientalis was evaluated by Baumann et al. (in press) through high resolution laser ablation ICPMS of Ba, Mg, Co, and Cu. Approximately one-half of the NE Pa- cific sample showed a signal that the authors attributed to the California Current. Otolith δ18O was used to derive ranges of encountered temperatures for West Greenland Atlantic salmon Salmo salar by Power et al. (in press). Several noteworthy studies pertinent to stock mixing and population connectivity were published in 2014. Continued work on Atlantic bluefin tuna Thunnus thynnus stock discrimination using otolith δ13C and δ18O has emphasized new fishery regions and greater sample sizes. Rooker et al. (2014) showed that NE Atlantic and Mediterranean fisheries were ~100% comprised of Mediterranean-origin juveniles but uncovered substantial mixing by both eastern and western (Gulf of Mexico) stocks in the North Central Atlantic Ocean. Niklitschek et al. (2014) conducted otolith δ13C and δ18O analyses in an ambitious- ly scaled study to investigate the relative contributions of the Chile’s entire continental shelf and the Patagonian Inner Sea to recruitments of Patagonian grenadier Macruronus magellanicus, one of South America’s principal groundfishes. They discovered that shelf nurseries dominated recruitments but that the Inner Sea made important contributions (10–35%), and suggested contribution rates may vary due to oceanographic drivers such as the West Wind Current. In a similar effort to separate broad habitat types, Daroven and Halden (2014) found that NW Atlantic capelin Mallotus villosus adults collected in either beach or deep-water spawning habitats showed differences in early Sr and Ba otolith profiles. They suggested contingent structuring may be occurring on the basis of natal homing to either habitat type. Using otolith stable isotopes and Sr/Ca and Ba/Ca, Morat et al. (2014) inferred that Mediterranean Sea common sole Solea solea fisheries in France received contributions of nurseries distributed throughout the Gulf of Lions. Evaluation of principal assumptions in using otolith chemistry to derive stock origin or environmental histories continued to be pursued in 2014 papers. For example, Kajajian et al. (2014) reported that right and left sagittal otolith pairs of Paralichthys dentatus showed asymmetry in otolith composition. Javor and Dorval (2014) observed a weak latitudinal trend in Pacific sardine Sardinops sagax otolith δ18O that was largely driven by lower values for samples taken from Canadian waters. In a literature review of citation statistics, Starrs et al. (2014) noted dominant trends in applying otolith chemistry to dispersal ecology in scores of fishes. Applications leading to population structure and stock mixing applications were not addressed in the review.

5.1.8 Parasites A special issue of the journal Parasitology entitled Parasites in Fisheries and Mariculture was published in January 2015. This issue includes 7 reviews of the use of parasites as biological tags for stock discrimination in different parts of the world (Cantatore and Ti- mi, 2015; George-Nascimento and Oliva, 2015; Lester and Moore, 2015; MacKenzie and Hemmingsen, 2015; Marcogliese and Jacobson, 2015; Mattiucci et al. 2015; Reed, 2015), one paper providing a meta-analysis of the discriminatory power of parasites as tags (Poulin and Kamiya, 2015), one dealing with the problem of cryptic parasite species in biotag studies (Bray and Cribb, 2015), and one case study on a single commercially important host species (van der Lingen et al., 2015).

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Two other biological tag studies on Mediterranean fish were published. Infections of bluefin tunas Thunnus thynnus with monogeneans, digenean metacercariae and parasitic copepods from three localities suggested mixing of Mediterranean resident bluefin tunas with migrants from the Atlantic Ocean (Culurgioni et al., 2014). In the second study, 13 metazoan parasite taxa were identified from Mediterranean swordfish Xiphias gladius using morphological and molecular methods. Significant differences in infection levels were found between Mediterranean swordfish and those from four Atlantic regions, supporting the existence of a separate Mediterranean stock (Mattiucci et al. 2014). Two studies investigated the use of parasites as tags for fish in the western Atlantic. The metazoan parasite assemblages of the Brazilian codling Urophycis brasiliensis, caught at four locations in Brazilian and Argentinian coastal waters, were analysed and five long- lived larval and juvenile helminths were selected as tags. A comparison of their infection levels supported the existence of three different stocks of U. brasiliensis in the study area (Pereira et al., 2014). The second study analysed the metazoan parasite infracommunities of the black grouper Mycteroperca bonaci caught at two localities off the coast of Yucátan, México and identified some long-lived helminth larvae as potentially useful tags for stock identification (Espínola-Novelo et al., 2015). In South Africa, different levels of infection with a species of digenean metacercaria in- fecting the eyes of sardines Sardinops sagax caught off the southern and western coasts were analysed using generalized linear models (GLMs). The results supported the hypothesis of two stocks of sardine, but also indicated that they are not discrete and that some degree of mixing occurs between them (Weston et al., 2015).

5.1.9 Early life stages Dispersal during the egg and larval stage can define the extent of stock structure for a species and several recent studies demonstrate how early life stages can contribute to our understanding of population structure in marine resources. Langangen et al., (2014) estimated spatially specific mortality rates of cod (Gadus morhua) eggs and larvae in the Bar- ents Sea. Their approach combined information from the spring and summer Russian ichthyoplankton surveys with a coupled individual based model that covered a time period from 1959 to 1993. Their analysis showed that spatial variation in the mortality of early life stages may have a substantial impact on recruitment. Their results suggest that there may be trade-offs, as offshore regions of the Barents Sea may be more favourable for early survival, but larvae in these regions were less likely to be advected to favourable nursery areas. The development of a method to estimate spatially specific mortality rates for early life history stages could have important implications for understanding stock structure and recruitment in marine species. Zhang et al., (2015) used an individual based model to examine the transport and connectivity patterns of surfclam (Spisula solidissima) larvae in the northwest Atlantic. Model results demonstrate an along-shore connectivity pattern amongst subpopulations from southern New England to the Delmarva region. Connectivity was highest amongst adjacent regions, and most recruiting larvae were either retained locally or originated from an adjacent upstream population. However, the Georges Bank surfclam population appears to relatively isolated, as there was little evidence for connectivity between Georges Bank and other regions. Sensitivity analyses suggest that active larval behaviours increase dispersal distances and may lead to greater connectivity amongst subpopulations.

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DeCelles et al., (in press) used an individual-based model to investigate the transport of winter flounder (Pseudopleuronectes americanus) larvae spawned in coastal waters of the Gulf of Maine. Model results suggest that certain coastal spawning grounds used by winter flounder may serve as an important source of larvae to estuaries and nearshore nursery areas. The potential influx of coastal spawned larvae could have implications for the resilience and productivity of local populations, and may increase gene flow amongst subpopulations in the Gulf of Maine. Model results also indicated the potential for larval transport from the Gulf of Maine stock to nursery grounds in the southern New Eng- land/Mid-Atlantic stock, and larval exchange between these two stocks should be investigated further. Ospina-Alvarez et al., (in press) constructed a spatially explicit individual based model to investigate the transport and connectivity of European anchovy eggs and larvae from spawning grounds in the Gulf of Lions in the northwest Mediterranean Sea from 2003 to 2009. The initial locations and concentrations of anchovy eggs were informed by an acoustic survey that was conducted each year during the peak spawning period. The model quantified connectivity amongst regional subpopulations, and the results indicate substantial interannual variability in larval drift and the magnitude of recruitment. Esti- mates of larval retention vary across years, but model results suggest that retention rates may be relatively high under certain conditions. The plume emanating from the Rhone River was found to be an important determinant of recruitment success. Kool and Nichol (2015) described the development of an open source, four dimensional (3D x time) biophysical dispersal model that is capable of tracking large numbers of larvae over complex bathymetric surfaces. The model output is saved to a relational database to facilitate data analysis. The model was applied to study connectivity patterns for marine species amongst marine reserves in Australia.

5.1.10 Simulation approaches The application of simulation modelling to test alternative stock structure hypotheses and explore the implications of stock structure to assessment and management is steadily increasing. Here, we report on key recent papers applying simulation methods to improve understanding of stock structure. An interesting advance in the application of simulation methods was the use of simulation modelling to examine the implications of “where we draw the line” in terms of stock boundaries on stocks with isolation-by-distance stock structure (Spies et al. 2014). The study applied a one-dimensional stepping stone model with 10 demes to model isolation- by-distance structure in two species (Pacific cod (Gadus macrocephalus) in the Aleutian Islands and northern rockfish (Sebastes polyspinis) in the Eastern Bering Sea and Aleutian Islands). Overall the simulations demonstrated that splitting a management unit any- where performs better, in terms of avoiding overfishing and maximizing yield, than not splitting it at all, when IBD stock structure is present. Hintzen et al. (2015) used simulation modelling in a management strategy evaluation framework to evaluate the role fisheries-independent surveys can play in an assessment when fisheries and surveys contain mixtures of population units. Failure to account for mixing was shown to be one of the major drivers of biased estimates of population abundance, affecting biomass reference points and MSY targets. Furthermore, the simulations

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demonstrated that when mixing of population units occurs, the role a survey can play to provide unbiased assessment results is limited. Without correct classification of the origin of fish from relatively smaller population units was important, these units are extremely vulnerable to overexploitation.

5.1.11 Interdisciplinary analysis Over the last two decades, SIMWG has adopted, developed and applied an interdisciplinary approach to determining the most likely biological population structure and the most appropriate practical management units. The general approach was applied to the specific terms of reference that are detailed in following sections, and the scientific community continues to apply and further develop the approach as a best practice in stock identification. Several case studies were contributed to the discipline over the last year. The STOCKMED project applied a holistic approach to the stock identification for 19 commercially important species in the Mediterranean (Fiorentino et al. 2014). The large group of collaborators critically reviewed all the available data and publications on growth, maturity, parasites, genetics, habitats and oceanography. They developed a methodology to standardize and integrate heterogeneous data. The methodology was based on spatially-explicit information, using Geographic Information Systems (GIS), spatial analyses, and Multi-Criteria Decision Analysis (MCDA) for multidisciplinary inferences. For practical management considerations, spatial distributions of biological groups were compared with information on the distribution of fishing fleets to identify relatively homogeneous stocks areas to be considered homogeneous for stock assessment and fisheries management. Applications ranged from relatively data-rich to data-poor situations. The collaborators recommend frequent updating of interdisciplinary analyses as knowledge gaps are filled. They identified early life history dispersal studies, the use of advanced genetic markers, and otolith microchemistry as priorities. Welch et al. (2014) provide a holistic evaluation of grey mackerel off northern Australia, considering information on genetics (mtDNA and microsatellites), parasites, otolith chemistry, and growth data from the same specimens. They confront the challenge of analyzing and interpreting patterns of variation from multiple disciplines using a multidisciplinary matrix of pairwise comparisons among sample locations. Their results suggest that grey mackerel are relatively ‘population-rich’, and they recommend six stocks for management purposes. McBride (2014) reviewed the stock identification methods and information used to define stock boundaries for the 25 species managed by the Atlantic States Marine Fisheries Commission, distributed between Maine and Florida, USA and adjacent areas. Stock identification methods included life history traits, other phenotypic traits, genetic traits, natural marks, and applied marks. Interdisciplinary analysis has been applied for a few species. Some marine and catadromous species are assessed and managed as a single unit stock, whereas others are divided into two stocks at Cape Hatteras, which is a major biogeographic boundary. Estuarine and anadromous spawners are managed at finer spatial scales. Most stock boundaries were largely influenced by larval dispersal and mixing of adults in marine environments. Clinal variation of phenotypic characters has contributed to several debates about stock structure. Strategic application of interdisciplinary stock identification is advocated.

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Holmes et al. (2014) examined trends in local spawning-stock biomass among putative stocks based on patterns in vital rates and local fisheries. Spawning group boundaries were delineated based on genetic, tagging, otolith microchemistry, and resource distributions from research vessel surveys. They found asynchronous trends in spawning stock within current cod and whiting stocks. Trends were different between cod from an inshore spawning group and larger offshore spawning group. Trends were also different between northern and southern spawning groups of whiting in the North Sea. No asynchrony was found in North Sea and west of Scotland haddock stocks. For cod and whiting, the combination of distinct spawning groups in stock assessment has masked the different trends in spawning groups. The study demonstrates an interdisciplinary approach to re-evaluating stock identity and the consequences of a mismatch between biological groups and management units. Zemeckis et al. (2014) reviewed all the available information for a multidisciplinary investigation of Atlantic cod in US waters. They conclude that inshore spawning components off Cape Cod and in southern New England are more connected than with inshore spawning components in the Gulf of Maine than on eastern Georges Bank. This perception of biological population structure does not match current management unit boundaries. They advocate for a modification of current stock boundaries to provide a more accurate representation of biological population structure. Until a method is developed to efficiently estimate stock composition of winter and spring-spawning components, separate assessment and management of inshore and offshore spawning components would improve the representation of natural spawning components. McKeown et al. (2015) integrated information from microsatellites and mtDNA with information from otolith chemistry to investigate stock structure and dispersal of Patagoni- an hoki. Analysis of samples from spawning adults off Chile and three feeding ground samples indicated a high level of connectivity among spawning aggregations. Despite this connectivity, genetic data and otolith core chemistry suggest a reproductively isolated population within the overwintering stock. These perceptions of biological population structure do not match the current Atlantic and Pacific management units. Turner et al. (2015) combined otolith chemistry and genetics to discriminate river herring populations. Classification accuracy of discrimination based otolith chemistry variables were improved when classifying individuals to regional genetic stocks. Conversely, at- tempts to classify at finer geographic scales did not perform as well. Their case study demonstrates the importance of identifying possible groups in discriminant analysis and the potential for using information from other disciplines for the prior identification of groups. Valentin et al. (2014) combined microsatellites and geometric morphometrics to study redfish (Sebastes spp.) population structure in the Northwest Atlantic (Gulf of Maine to Labrador). There was good agreement between the genetic and morphometric data sets which both supported weak but consistent population structure for S. mentella and S. fasciatus in the study area. For S. mentella, the data supported a single biological population for the Gulf of St. Lawrence- Laurentian Channel (GSL-LCH) area with some indication of introgressive hybridization with S. fasciatus, a sink population from the GSL-LCH in the Saguenay fjord (Quebec, Canada), and two populations segregated by depth in the Labrador Sea. For S. fasciatus, the authors’ analysis showed the presence of a highly distinct population in the Bonne Bay fjord (Newfoundland, Canada), as well as weak popu-

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lation structure at a large geographic scale between the GSL-LCH area, the Gulf of Maine, and the continental slope from the northern Grand Banks to the mouth of the Laurentian Channel. Darnaude et al. (2014) used interdisciplinary analysis to improve discrimination of three offshore European plaice Pleuronectes platessa sub-stocks in the North Sea using otolith chemistry and archival tagging. Data from a decade of archival tag deployments were used to derive monthly distributions of the fish and corresponding temperature and salinity estimates and to predict δ18O values. The approach achieved >96% correct predic- tion of sub-stock membership using seasonal δ18O values. However, the use of annual δ18O values did not perform as well for stock identification, demonstrating that seasonal behavior and habitats should be considered in the interpretations of otolith chemistry analyses. For Northeast Artic cod, Michalsen et al. (2014) combined information from DSTs and molecular genetics to acquire a deeper understanding of individual behaviour and the spatial dynamics of the resource. An increase in the frequency of interdisciplinary approaches is anticipated in the future given continued advancements in both tagging technologies and laboratory techniques. Fraker et al., (2015) used microsatellite DNA and otolith chemistry to investigate the pa- rental origins of yellow perch (Perca flavescens) larvae in Lake Erie, USA. As part of their analysis, they re-assigned larvae to their hatching site, based on the results of a particle back tracking (i.e., hindcasting) model, which was used to reconstruct the dispersal pathways travelled by the larvae. They found that using the back tracking model improved the ability of the genetic and otolith microchemistry techniques to discriminate amongst local breeding subpopulations. Their results suggest that using particle backtracking could be an important tool for stock composition analysis of marine species. Another emerging approach to stock identification is the application of genetic techniques to identifying parasite species that were previously difficult or impossible to identify, thereby greatly expanding the power and interpretability of parasites as natural tags for stock identification. Several recent interdisciplinary studies found that current management units do not match new perceptions of biological structure. For such situations, expert groups like SIMWG are required to review recent scientific contributions and advise managers on practical management units.

5.2 ToR b) Build a reference database with updated information on known biological stocks for species of ICES interest

5.2.1 Summary of workplan and progress on database At the annual meeting, SIMWG members discussed the desire to build a repository to hold past reviews conducted by SIMWG scientists on issues of stock identity for ICES species. The group proposed developing a table that would summarize existing reviews by SIMWG with the idea that the table would eventually include hyperlinks to the full- text reviews. SIMWG discussed the challenge of communicating the existence of stock identity reviews for ICES species that reside within our annual reports. The members felt that producing a database of past work will serve both the working group and the broader ICES community.

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To date, we developed two tables designed to summarize history and progress of SIMWG by reviewing reports dating back to 1998. Table 1 (Annex 4) provides a history of SIMWG activity, summarizing previous chairs, meeting locations, terms of reference, as well as the species for which issues of stock identity were reviewed. Table 2 (Annex 4) summarizes existing species-specific reviews providing more detail on the ICES stocks and ecoregions. In preparation for developing a database of species reviews, we have adopted a standard format for reporting technical advice on ICES species. In the coming year we plan to excerpt past reviews from our annual reports so that they will serves as stand-alone reports. Next steps will include establishing a working agreement with ICES web designers for delivery of a SIMWG reference database on biological stocks for ICES species of interest.

5.2.2 Technical reviews This year SIMWG was asked to provide technical advice on questions of stock identity for the ICES species listed below. The full reviews are contained in the annex of this report. Annex 5: Evaluation of greater silver smelt stock identity in ICES Subareas I, II, IV, VI, VII, VIII, IX, X, XII and XIV and Divisions IIIa and Vb Annex 6: Evaluation of Plaice Stock Identity in ICES sub-area IIIa and Adjacent Areas Annex 7: Evaluation of haddock stock identity in ICES Subareas IV and VIa (North Sea and West of Scotland) Annex 8: Evaluation of European anchovy stock Identity in ICES Division IXa Annex 9: Evaluation of megrim stock identity in ICES Subareas VIIIc and IXa

5.3 ToR c) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment. In recent years, there have been advancements in the field of mixed stock analysis (MSA) and new applications of the approach, which are relevant to ICES science and advice. Here, we focus our review of advances in mixed stock analysis on the key aspect of baselines (development, advances, and best practices), as this remains the single most important constraint for a sound application of MSA and other assignment-based methods. We also report on new application of mixed stock analysis to ICES species of interest in the past year.

Advances in Mixed Stock Analysis: Baselines

Genetic Baselines Genetic baselines continue to be the basis for analysing mixtures of fish from multiple sources to estimate stock composition or to assign individuals to their respective sources. Development of the baseline in terms of attaining accuracy and precision generally depends on two main factors: i) the robust characterisation of all possible biological populations contributing to a fishery; ii) the availability of reliable, informative loci. Therefore, repeated evaluation of the genetic baseline to determine its utility is an essential component of baseline development. Garvin et al. (2014) introduced a novel method for evaluat-

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ing a genetic baseline called “leave-ten-percent-out cross-validation” (LTO) that is derived from K-fold cross-validation of classification statistics. This method avoids the op- timism of other evaluation methods, uses only observed multi-locus genotypes, accepts haploid and diploid data, applies Bayesian methods of mixed-stock analysis, and is less dependent on large baseline sample sizes. Garvin et al. (2014) also introduced a method for simulating increasing numbers of single nucleotide polymorphism (SNP) loci and using LTO and logistic regression to forecast the number of informative SNP loci that would be necessary to achieve a specified rate of correct assignment of individuals to stock of origin.

Recent Applications of Genetic Mixed Stock Analysis In recent years, most of the development in MSA has occurred with anadromous species, salmonids in particular, because baselines are circumscribed to local riverine habitats and levels of population differentiations are substantial. Studies of Chinook (King) salmon (Oncorhynchus tshawytscha) have driven advances in this field, with a rapid shift from microsatellite to SNP baseline characterisation, which now offer an exhaustive pool of reference baseline genotypes across the whole North Pacific arch, from Southern Japan to California (Seeb et al. 2011; Templin et al. 2011). These baselines have allowed reconstruc- tion of migration, habitat use and catch contributions from sea samples between Kam- chatka and Alaska (Larson et al. 2013) and in California (Clemento et al. 2014). In both cases, the patterns recovered were investigated over multiple years and validated with other data arising from tagging and parasites. Following this lead, similar SNP-based approaches are being also applied to Sockeye salmon (Oncorhynchus nerka; Gilk-Baumer et al. 2015), confirming the power and effectiveness of this approach and laying the foun- dations for long-term usage of readily available SNP genotypic information for reference baselines. Genetic mixed-stock analysis continues to be a powerful tool not only by providing information on the composition of current fisheries but also offering insights on temporal changes in population proportions in catches and the causes of those changes. Using individual assignment of Atlantic salmon to stock of origin, Kallio-Nyberg et al. (2014) inferred spawning-age distributions and sex-ratios of spawners in Baltic Sea salmon stocks. Based on a comparison of contemporary data to published historical data from the 1930s, before hatchery rearing and offshore fishing, they were able to document temporal changes in spawning-age distributions. Differences in spawning age, an adaptive trait, were examined in the context of changing environmental conditions and human-caused activity such as habitat loss, fishery selection, hatchery rearing, etc. Their study demonstrated that compared to historical data, variation in spawning age has become narrower and more skewed towards younger aged fish. Koljonen et al. (2014) compiled an unprecedented multinational genetic baseline of sea trout (Salmo trutta) populations in the Gulf of Finland. The baseline of 59 populations and 15 microsatellite loci was effective in resolving the composition of Finnish coastal sea trout catches. The complex catches were mixtures of hatchery and wild fish from Estoni- an, Finnish, and Russian populations of varying size. The expectation was that the majority of the catches would derive from the hatchery smolts stocked in Finland, under the assumption that sea trout do not migrate regularly over long distances in the sea. Genetic MSA did indeed confirm that over 70% of the catches were constituted by Finnish hatch-

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ery fish, but also revealed an unexpectedly high proportion of Russian and Estonian wild sea trout (at least one-fifth) in the Finnish catches. In addition, a greater proportion of fish came from Estonia than Russia, although the Russian coast is geographically closer. The new information revealed by genetic MSA highlights the importance of MSA for the conservation and management of fish species. A recent trend towards the use of “outlying” SNP markers has also been initiated with the aim to reduce the number of markers required for population assignment (Acker- mann et al. 2011) and to maximise the levels of differentiation between putative stocks in marine species with high gene flow, large effective population size and less distinct population boundaries (Nielsen et al. 2012). Although it remains problematic to predict to what extent the signal from these outlying loci will remain stable over time and how it will match the connectivity between population units, recent evidence in Atlantic salmon suggests that patterns of population structure obtained with neutral and adaptive markers may be highly consistent (Moore et al. 2014). In fully marine species, given the intrin- sic limitations associated with identification of reliable and stable baselines and the less distinct boundaries between them, MSA is still lagging behind. Outside the known in- vestments in ‘classic’ North Atlantic species, such as cod and herring, a recent microsatellite-based investigation of small yellow croaker (Larimichthys polyactis) in the Yellow Sea and the East China Sea effectively reconstructed contributions of coastal stocks to mixed fisheries (Wang et al. 2015), suggesting that fishery aggregations are mostly seeded by regional/local stocks. This example shows that there may be several cases of commercially exploited species for which a relatively limited pool of traditional markers could still offer useful insights for management, but the key in any case remains the knowledge and provision of robust and reliable baselines.

Otolith Chemistry Baselines Otolith chemistry baselines are increasingly used to support mixed-stock analysis (Kerr and Campana 2014). A historical literature largely focused on testing habitat-otolith chemistry associations is beginning to address practical applications in evaluating central stock structure questions such as natal homing and population connectivity. Applica- tions are most rigorously applied when the following criteria are met: 1 ) Otolith chemistry aliases physiochemical attributes of natal habitats for each component stock. 2 ) Otolith chemistry baselines are representative of all natal habitats for each component stock. 3 ) Otolith chemistry baselines are stable OR can be matched to test mixed stock samples through year-class matching. The topic of otolith’s incorporation of metals and isotopes in relation to ambient exposure has received intensive research, albeit relatively few examples exist for controlled exper- imentation (Elsdon et al. 2008). Most studies have relied on field observations to support correlations between environmental chemistry and otolith composition. Established models of otolith tracers of natal habitats exist for isotopes of Sr, Ba, Mn, and stable isotopes of oxygen and carbon (Elsdon et al. 2008; McMahon et al. 2013; Kerr and Campana 2014). Promising new models are being developed to trace natal habitat food webs utilizing amino acid carbon stable isotopes, which occur at trace levels in otoliths (McMahon et

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al. 2011). Measurement error of otolith composition is a topic of concern in developing ambient tracers, with potential issues of instrument sensitivity, contamination, and biases caused by isobaric interference, inadequate standardization and reference materials, and instrumental drift (Campana et al. 1997; Secor et al. 2002). In mixed-stock analysis, otoliths will provide information on natal origins (e.g., early larval and juvenile habitats). This is different than other tracers, which indicate lineage or spawning site fidelity (Secor 2015). Still natal homing is a fundamental attribute in dis- criminating populations that are defined by geographically bounded natal habitats. For some species and populations, natal habitats may be expansive, numerous, patchily distributed, or temporally unstable in distribution. In such instances, obtaining a representative natal otolith composition for the entire population requires careful sampling design considerations and in some instances may not be feasible (e.g., Clarke et al. 2009). As in other stock discrimination approaches (see Genetic Baselines), missed populations (natal areas) can result in poor management advice: for instance, a minority stock makes no contribution to a mixed stock fishery. Natal habitat baselines are likely to be unstable year-to-year owing to changing oceanographic conditions. Two approaches have been used to address unstable baselines: (1) verification of stable baselines owing to persistent oceanographic differences between natal areas; and (2) year-class matching (aka otolith composition atlas). The epitome example of the former approach is for Atlantic bluefin tuna Thunnus thynnus, for which there are two populations that occupy very different natal habitats on either side of the North Atlantic. Juveniles of the western stock occupy the Gulf of Mexico and US Atlantic shelf waters; those of the eastern stock occupy the Mediterranean Sea. The Mediterrane- an Sea is evaporative and dominated by oceanic waters leading to persistently higher ambient levels of δ18O, which is manifest in otolith composition. These differences in otolith composition persisted over 15 years of sampled yearling juveniles in either natal habitat (Rooker et al. 2014). Despite this long-term persistence in the bluefin tuna baselines, future decades will likely see changed ambient exposure of δ18O owing to atmospheric composition changes (Schoesser et al. 2009; Siskey 2015). In a pioneering application on US Mid-Atlantic weakfish Cynoscion regalis, Thorrold et al. (2001) matched young-of-the-year otolith juvenile composition from collections in year t, to yearling juvenile otolith in year t+1, thus tracking otolith composition for the same year-class. Here, numerous estuarine nursery areas were sampled to support analysis of natal contributions to mixed fisheries occurring in US Atlantic shelf waters. This application supported important inferences on contributions of estuaries to adjacent shelf fisheries. Year-class matching depends strongly on the ability to follow year-classes (age precision). Further, for more operational use, year-class matching would require baselines to be developed across multiple years. This approach has been referenced as an atlas approach whereby a matrix of otolith composition by natal region x year could be matched with a mixed-stock fish according to its assigned year-class. Although strongly promoted (e.g., Palumbi 2004; Ruttenberg and Warner 2006), an otolith composition atlas has yet to be realized.

Otolith Shape Mixed Stock Analysis: Application to Norwegian cod Growth patterns in otoliths of Atlantic cod (Gadus morhua) off Norway and in the Barents Sea are commonly used to differentiate between coastal and Northeast Arctic cod, which

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occur as mixed stocks in several of their distribution areas. This is an example of the application of mixed stock analysis that has been fully integrated into stock assessment and management. The shape of the increment patterns in otolith cross-sections has been utilized by age readers to categorize cod into one of the two stocks since the 1930s. Berg et al. (2005) attempted to quantify the variation in growth increment (annuli) forms and reported on the problem of capturing the entire increment outline due to unclear structures in parts of the increment band. Stransky et al. (2008), however, were able to differentiate the two stocks with 90% certainty by using Fourier shape analysis of the whole-otolith outlines. This study also directly compared the classification of cod by otolith shape, which involved some subjectivity in categorization/typing by age readers, to classification by genetic types. Baselines still need to be fully evaluated for this application; however, Stransky et al. (2008) revealed that the origin of cod can be determined with a high degree of certainty using otolith shape analysis. SIMWG will continue to work on this ToR to address the issue of how mixed-stock analysis can be best utilized to improve stock assessment and management.

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Kool, J.T., and Nichol, S.L. 2015. Four-dimensional connectivity modeling with application to Aus- tralia’s north and northwest marine environments. Environmental Modelling and Software. 65: 67-78.

Langangen, Ø., Stige, L.C., Yaragina, N.A., Ottersen, G., VikebØ, F.B., and Stenseth, N.C. 2014. Spa- tial variations in mortality in pelagic early life stages of a marine fish (Gadus morhua). Progress in Oceanography 127: 96-107.

Langård, L., Skaret, G., Jensen, K.H., Johannessen, A., Slotte, A., Nøttestad, L., and Fernö, A. 2015. Tracking individual herring within a semi-enclosed coastal marine ecosystem: 3-dimensional dynamics from pre- to post-spawning. Marine Ecology Progress Series. 518: 267-279.

Larson, W.A. et al. 2013. Single-nucleotide polymorphisms reveal distribution and migration of Chinook salmon (Oncorhynchus tshawytscha) in the Bering Sea and North Pacific Ocean. Cana- dian Journal of Fisheries and Aquatic Science. 70: 128–141.

Le Bris, A., Fréchet, A., Galbraith, P.S., and Wroblewski, J.S. 2013a. Evidence for alternative migratory behaviours in the northern Gulf of St Lawrence population of Atlantic cod (Gadus morhua L.). ICES Journal of Marine Science, 70(4): 793-804.

Le Bris, A., Fréchet, A., and Wroblewski, J.S. 2013b. Supplementing electronic tagging with conventional tagging to redesign fishery closed areas. Fisheries Research. 148: 106-116.

Lester, R.J.G. and Moore, B.R. 2015. Parasites as valuable stock markers for fisheries in Australasia, East Asia and the Pacific Islands. Parasitology. 142: 36-53.

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Lidgard, D.C., Bowen, W.D., Jonsen, I.D., and Iverson, S.J. 2014. Predator-borne acoustic transceiv- ers and GPS tracking reveal spatiotemporal patterns of encounters with acoustically tagged fish in the open ocean. Marine Ecology Progress Series. 501: 157-168.

MacKenzie, K. and Hemmingsen, W. 2015. Parasites as biological tags in marine fisheries research: European Atlantic waters. Parasitology. 142: 54-67.

Marcogliese, D.J. and Jacobson, K.M. 2015. Parasites as biological tags of marine, freshwater and anadromous fishes in North America from the tropics to the Arctic. Parasitology. 142: 68-89.

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Mattiucci, S., Cimmaruta, R., Cipriani, P., Abaunza, P., Bellisario, B. and Nascetti, G. 2015. Integrat- ing Anisakis spp. parasites data and host genetic structure in the frame of a holistic approach for stock identification of selected Mediterranean Sea fishes. Parasitology. 142: 90-108.

Mattiucci, S., Garcia, A., Cipriani, P., Santos, M.N., Nascetti, G. and Cimmaruta, R. 2014. Metazoan parasite infection in the swordfish, Xiphias gladius, from the Mediterranean Sea and comparison with Atlantic populations: implications for its stock characterization. Parasite. 21: 35.

McBride, R.S. 2014. Managing a Marine Stock Portfolio: Stock Identification, Structure, and Man- agement of 25 Fishery Species along the Atlantic Coast of the United States, North American Journal of Fisheries Management, 34:4, 710-734. http://dx.doi.org/10.1080/02755947.2014.902408

McBride, R. S., Wuenschel, M. J., Nitschke, P., Thornton, G. & King, J. R. 2013. Latitudinal and stock-specific variation in size- and age-at-maturity of female winter flounder, Pseudopleu- ronectes americanus, as determined with gonad histology. Journal of Sea Research. 75: 41-51.

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McKeown, N.J., Arkhipkin, A.I. and Shaw, P.W. 2015. Integrating genetic and otolith microchemistry data to understand population structure in the Patagonian Hoki (Macruronus magellanicus). Fisheries Research. 164: 1-7. doi:10.1016/j.fishres.2014.10.004

McMahon, K. W., M. L. Berumen, I. Mateo, T. S. Elsdon, and S. R. Thorrold. 2011. Carbon isotopes in otolith amino acids identify residency of juvenile snapper (Family: Lutjanidae) in coastal nurseries. Coral Reefs. 30(4):1135-1145.

McMahon, K. W., L. L. Hamady, and S. R. Thorrold. 2013. Ocean ecogeochemistry: a review. Oceanography and Marine Biology: an Annual Review. 51: 327-373.

Michalsen, K., Johansen, T., Subbey, S., and Beck, A. 2014. Linking tagging technology and molecular genetics to gain insight in the spatial dynamics of two stocks of cod in the Northeast Atlan- tic waters. ICES Journal of Marine Science, 71(6): 1417-1432.

Midway, S.R., Cadrin, S.X., and Scharf, F.S. 2014. Southern flounder (Paralichthys lethostigma) stock structure inferred from otolith shape analysis. Fisheries Bulletin. 112: 326-338.

Midway, S. R., Wagner, T., Arnott, S. A., Biondo, P., Martinez-Andrade, F. & Wadsworth, T. F. 2015. Spatial and temporal variability in growth of southern flounder (Paralichthys lethostigma). Fisheries Research. 167: 323-332.

Milano, I., Babbucci, M., Cariani, A., and 16 other authors. 2014. Outlier SNP markers reveal fine- scale genetic structuring across European hake populations (Merluccius merluccius). Molecular Ecology. 23: 118-135.

Moore, J.-S. et al., 2014. Conservation genomics of anadromous Atlantic salmon across its North American range: outlier loci identify the same patterns of population structure as neutral loci. Molecular Ecology. 23: 5680-5697.

Morat, F., Y. Letourneur, J. Dierking, C. Pecheyran, G. Bareille, D. Blamart, and M. Harmelin- Vivien. 2014. The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints. Plos One. 9(1).

Morris, C.J., Green, J.M., Snelgrove, P.V.R., Pennell, C.J., and Ollerhead, L.M.N. 2014. Temporal and spatial migration of Atlantic cod (Gadus morhua) inside and outside a marine protected area and evidence for the role of prior experience in homing. Canadian Journal of Fisheries and Aquatic Sciences. 71: 1-9.

Neat, F.C., Bendall, V., Berx, B., Wright, P.J., Cuaig, M.Ó., Townhill, B., Schön, P.-J., Lee, J., and Righton, D. 2014. Movement of Atlantic cod around the British Isles: implications for finer- scale stock management. Journal of Applied Ecology. 51: 1564-1574.

Neuenfeldt, S., Righton, D., Neat, F., Wright, P.J., Svedäng, H., Michalsen, K., Subbey, S., Steingrund, P., Thorsteinsson, V., Pampoulie, C., Andersen, K.H., Pedersen, M.W., and Metcalfe, J. 2013. Analysing migrations of Atlantic cod Gadus morhua in the north-east Atlantic Ocean: then, now and the future. Journal of Fish Biology. 82: 741-763.

Nielsen, E. E., et al. 2012. Gene-associated markers provide tools for tackling IUU fishing and false eco-certification. Nature Communications. 3: 851.

Niklitschek, E. J., D. H. Secor, P. Toledo, X. Valenzuela, L. A. Cubillos, and A. Zuleta. 2014. Nursery systems for Patagonian grenadier off Western Patagonia: large inner sea or narrow continental shelf? ICES Journal of Marine Science. 71(2): 374-390.

Oliver, M.J., Breece, M.W., Fox, D.A., Haulsee, D.E., Kohut, J.T., Manderson, J., and Savoy, T. 2013. Shrinking the haystack: using an AUV in an integrated ocean observatory to map Atlantic sturgeon in the coastal ocean. Fisheries. 38(5): 210-216.

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Ospina-Alvarez, A., Catalan, I.A., Bernal. M., Roos, D., and Palomera, I. In press. From egg production to recruits: connectivity and inter-annual variability in the recruitment patterns of Euro- pean anchovy in the northwest Mediterranean. Progress in Oceanography.

Padilla, A., R. Brown, and M. Wooller. In Press. Strontium isotope analyses (87Sr/86Sr) of otoliths from anadromous Bering cisco (Coregonus laurettae) to determine stock composition. ICES Journal of Marine Science.

Palumbi, S. R. 2004. Marine reserves and ocean neighborhoods: The spatial scale of marine populations and their management. Annual Review of Environment and Resources 29: 31-68.

Pampoulie, Christophe; Skirnisdottir, Sigurlaug; Olafsdottir, Guobjorg; et al.2014 Genetic structure of the lumpfish Cyclopterus lumpus across the North Atlantic ICES Journal of Marine Science. 71(9): 2390-2397.

Pereira, A.N., Pantoja, C., Luque, J.L. and Timi, J.T. 2014. Parasites of Urophycis brasiliensis (Gadi- formes: Phycidae) as indicators of marine ecoregions in coastal areas of the South American Atlantic. Parasitology Research. 113: 4281-4292.

Petersen, P. E. 2014. An investigation of genetic and reproductive differences between Faroe Plat- eau and Faroe Bank cod (Gadus morhua L.). Thesis, University of Stirling (http://hdl.handle.net/1893/21613).

Poulin, R. and Kamiya, T. 2015. Parasites as biological tags of fish stocks: a meta-analysis of their discriminatory power. Parasitology 142: 145-155.

Power, M., V. Minke-Martin, B. Dempson, and T. Sheehan. In Press. Otolith-derived estimates of marine temperature use by West Greenland Atlantic salmon (Salmo salar). ICES Journal of Ma- rine Science.

Reed, C.C. 2015. A review of parasite studies of commercially important marine fishes in sub- Saharan Africa. Parasitology. 142: 109-124.

Rooker, J.R., H. Arrizabalaga, I. Fraile, D.H. Secor, D.L. Dettman, N. Abid, P.Addis, S. Deguara, F. Saadet Karakulak, A. Kimoto, O. Sakai, D. Macías, M. Neves Santos. 2014. Crossing the line: migratory and homing behaviors of Atlantic bluefin tuna. Marine Ecology Progress Series. 504: 265-276.

Ruttenberg, B. I., and R. R. Warner. 2006. Spatial variation in the chemical composition of natal otoliths from a reef fish in the Galapagos Islands. Marine Ecology Progress Series. 328: 225-236.

Schloesser, R.W., J.R. Rooker, P. Louchuoarn, J.D. Neilson, and D.H. Secor. 2009. Inter-decadal variation in ambient oceanic δ13C and δ18O recorded in fish otoliths. Limnology and Oceanogra- phy. 54(5): 1665-1668.

Secor, D.H. 2015. Migration Ecology of Marine Fishes. Johns Hopkins University Press. 304 p.

Secor,D.H, S.E. Campana, V.S. Zdanowicz, J.W.H. Lam, L. Wang, and J.R. Rooker. 2002. In- ter-laboratory comparison of Atlantic and Mediterranean Bluefin tuna otolith microconstitu- ents. ICES Journal of Marine Science. 59: 1294-1304.

Seeb, L.W. et al. (2011) Single nucleotide polymorphisms across a species’ range: implications for conservation studies of Pacific salmon. Molecular Ecology Resources. 11 (Suppl. 1), 195–217.

Shum, P., Pampoulie, C., Kristinsson, K. and Mariani, S. 2015. Three-dimensional post-glacial ex- pansion and diversification of an exploited oceanic fish. Molecular Ecology 24: 3652–3667.

Sippel, T., Everson, J.P., Galuardi, B., Lam, C., Hoyle, S., Maunder, M., Kleiber, P., Carvalho, F., Tsontos, V., Teo, S.L.H., Aires-da-Silva, A., and Nicol, S. 2015. Using movement data from electronic tags in fisheries stock assessment: a review of models, technology and experimental design. Fisheries Research, 163: 152-160.

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Siskey, M.R. 2015. Historical effects of fishing on age structure and stock mixing in Northwest Atlantic bluefin tuna. In Marine Estuarine and Environmental Sciences, p.159. College Park: University of Maryland.

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Stanley, R.R.E., deYoung, B., Snelgrove, P.V.R., and Gregory, R.S. 2013. Factors regulating early life history dispersal of Atlantic cod (Gadus morhua) from coastal Newfoundland. PLoS ONE 8(9): e75889.

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Stransky, C., Baumann, H., Fevolden, S.E., Harbitz, A., Høie, H., Nedreaas, K., Salberg, A.B., and Skarstein, T.H. 2008. Separation of Norwegian coastal cod and Northeast Arctic cod by outer otolith shape analysis. Fisheries Research. 90: 26-35.

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Valentin, A. E., Penin, X., Chanut, J.-P., Power, D., Sevigny, J.-M. 2014. Combining microsatellites and geometric morphometrics for the study of redfish (Sebastes spp.) population structure in the Northwest Atlantic. Fisheries Research 154: 102-119.

van der Lingen, C.D., Weston, L.F., SSempa, N.N. and Reed, C.C. 2015. Incorporating parasite data in population structure studies of South African sardine Sardinops sagax. Parasitology 142: 156- 167.

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Welch, D. J., S. J. Newman, R. C. Buckworth, J. R. Ovenden, D. Broderick, R. J. G. Lester, N. A. Gribble, A. C. Ballagh, R. A. Charters, J. Stapley, R. Street, R. N. Garrett, and G. A. Begg. 2014. Integrating different approaches in the definition of biological stocks: A northern Australian multi-jurisdictional fisheries example using grey mackerel, Scomberomorus semifasciatus. Marine Policy. 55: 73-80.

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Weston, L.F., Reed, C.C., Hendricks, M., Winker, H. and van der Lingen, C.D. 2015. Stock discrimination of South African sardine (Sardinops sagax) using a digenean parasite biological tag. Fish- eries Research. 164: 120-129.

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Zhang, X., Haidvogel, D., Munroe, D., Powell, E.N., Klinck, J., Mann, R., and Castruccio, F.S. 2015. Modeling larval connectivity of the Atlantic surfclams within the middle Atlantic Bight: model development, larval dispersal and metapopulation connectivity. Estuarine, Coastal and Shelf Science. 153: 38-53.

7 Revisions to the work plan and justification

Revised SIMWG Multiannual ToR: a ) Review recent advances in stock identification methods; b ) Build a reference database with updated information on known biological stocks for species of ICES interest; c ) Provide technical reviews and expert opinions on matters of stock identification, as requested by specific Working Groups and SCICOM; d ) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment.

8 Next meetings

SIMWG plans to work by correspondence in 2015–2016.

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Annex 1: List of participants

Name Address Email

Steve Cadrin UMass Dartmouth, 200 Mill [email protected] Road, Suite 325 Fairhaven, MA 02719 U.S.A. Greg Decelles [email protected] UMass Dartmouth, 200 Mill Road, Suite 325, Fairhaven, MA 02719 U.S.A Lisa Kerr (Chair) [email protected] Gulf of Maine Research Insti- tute, 350 Commercial St. Port- land, ME 04101, U.S.A. Ken Mackenzie [email protected] The University of Aberdeen, (by correspondence) King's College, Aberdeen, AB24 3FX, Scotland Stefano Mariani University of Salford, Room [email protected] 316, Peel Building, Salford M5 4WT, UK Michele Masuda Alaska Fisheries Science Cen- [email protected] (by correspondence) ter, 17109 Pt. Lena Loop Rd., Juneau, AK 99801, U.S.A.

Richard McBride National Marine Fisheries [email protected] Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, U.S.A. David Secor [email protected] University of Maryland Cen- ter for Environmental Science, Chesapeake Biological Labor- atory, PO Box 38, Solomons, Maryland

Christoph Stransky [email protected] Institute of Sea Fisheries, Jo- hann Heinrich vonThünen, Bundesallee 50, Braunschweig 38116,Germany

Graham Sherwood (chair Gulf of Maine Research Insti- [email protected] invited) tute, 350 Commercial St. Port- land, ME 04101, U.S.A.

Doug Zemeckis UMass Dartmouth, 200 Mill [email protected] Road, Suite 325, Fairhaven, MA 02719 U.S.A

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Annex 2: Recommendations

RECOMMENDATIONS FOR FOLLOW UP BY: 1. Technical support will be required from ICES for SIMWG, ICES Secretariat, SCICOM establishment of a reference database of SIMWG reviews on stock identity issues for ICES species. 2. SIMWG supports the newly revised stock unit for WGNSSK, WGCSE, SCICOM, ACOM haddock in ICES Subarea IV and VIa (North Sea and West of Scotland). 3. SIMWG does not find biological support for combining WGBIE, WGAGFM, SCICOM, ACOM the northern (ICES Divisions VIIb-k and VIIIabd) and southern (ICES Divisions VIIIc and IXa) stocks of megrim together and recommends that the current stock separation stands. 4. SIMWG does not find sufficient evidence to support WGHANSA, WGACEGG, SCICOM, ACOM changing the current stock unit for anchovy in ICES Division IXa (Bay of Biscay and Iberic waters). SIMWG recommends that the current stock structure stand and the approach of employing spatially explicit management and monitoring of ICES Subdivision IXa North, North Central, South Central, and South continue. 5. SIMWG does not find strong scientific evidence to WGDEEP, SCICOM, ACOM support the proposed revision of greater silver smelt stock units. SIMWG recommends that the current stock structure stand and that stock identification work on this species be prioritized. 6. SIMWG find there is a valid scientific basis to support WGNSSK, WGBFAS, SCICOM, ACOM the current ICES stock units for plaice in ICES sub-area IIIa and Adjacent Areas. SIMWG strongly recommends future work examining the mixed stock composition of fish in the transition region (Skagerrak, Kattegat).

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Annex 3: Agenda

Meeting Dates: 10-12 June 2015 Venue: Portland, Maine USA Chair: Lisa Kerr, USA ([email protected]) Professional secretary: Adi Kellermann ([email protected]) Support secretary: Maria Lifentseva ([email protected])

MEETING AGENDA Wednesday 10 June Morning (9:00 am-12:30 pm) 9:00-9:30 . Opening – L. Kerr (Chair) . Introductions and notifications 9:30-10:00 . Background (terms of reference, meeting objectives, meeting products) . Adoption of agenda and timetable 10:00-10:45 . Work session on Term of Reference a) Review advances in stock identification methods Workplan: Working group members will review recent literature on a particular method and will provide a brief summary to the group that summarizes applications to ICES species of interest and describes new approaches or novel combinations of existing applications. 10:45-11:00 COFFEE BREAK 11:00-12:00 . Continue work session on ToR a 12:30-2:00 LUNCH Afternoon (2:00-6:00 pm) 2:00-3:30 . Work session on Term of Reference b) Build a reference database with updated information on known biological stocks for species of ICES interest Workplan: Discuss the format for the reference database and connect with ICES web designers for planning of SIMWG reference database. 3:30-3:45 COFFEE BREAK 3:45-6:00 Workplan: SIMWG members will break into groups to provide technical advice on stock structure of ICES species as requested by other ICES working groups. 1. Megrim (Lepidorhombus whiffiagonis) in Divisions VIIIc and IXa and in VII and VIIIabd (review requested by WGBIE) 2. Haddock in North Sea and VIa areas (review requested by WKHAD)

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3. Other requests 7:00 GROUP DINNER AT PORTLAND RESTAURANT Thursday June 11 Morning (9:00 am-12:30 pm) 9:00-10:45 . Continue work session on technical advice 10:45-11:00 COFFEE BREAK 11:00-12:30 . Wrap-up work session on technical advice 12:30-2:00 LUNCH Afternoon (2:00-5:30 pm) 2:00-5:30 . Term of Reference c) Review and report on advances in mixed stock analysis, and assess their potential role in improving precision of stock assessment Workplan: Working group members will generate ideas through a discussion on the topic of mixed-stock analysis and how it can be best utilized to improve stock assessment and management and provide case study examples. We will try to address critical questions regarding how mixed-stock component estimates can affect reference points (e.g. MSY) of assessed stocks. 3:30-3:45 COFFEE BREAK 3:45-5:30 . Wrap-up work session on ToR c 6:00-8:00 Windjammer sailing trip in Casco Bay (~ $40 per person) Friday June 12 Morning (9:00-12:00) 9:00-10:00 . Synthesize report and identify gaps that need to be filled . Agree on recommendations. . Discuss next steps for SIMWG - new TOR - Work plan for 2015-2016 10:45-11:00 COFFEE BREAK 11:00-12:00 . Wrap-up discussion of next steps for SIMWG 12:00 Meeting adjourned

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Annex 4: ToR B – Tables

Table 1. History of SIMWG activity, including previous chairs, meeting locations, terms of reference, and species for which issues of stock identity were reviewed.

Year Species Reviews Meeting Chairs Terms of Reference

1997 No species reviewed By correspondence K. Friedland (Chair) USA a) continue development of the Stock Identification Methodology; b) advise on future meetings of the Working Group.

1998 No species reviewed By correspondence K. Friedland (Chair) USA a) continue development of the Stock Identification Methodology; b) advise on future meetings of the Working Group. a) continue development of the Stock Identification Methodology; b) advise on the need for future meetings of the Working Group, and prepare appropriate terms of reference if required; c) obtain peer-review of the Working Group report from a K. Friedland (USA) and 1999 No species reviewed By correspondence member of the Living Resources Committee prior to the 1999 Annual Science Conference; d) comment on the draft objectives J. Waldman (USA) and activities in the Living Resources Committee component of the ICES Five-Year Strategic Plan, and specify how the purpose of the Working Group contributes to it. K. Friedland (USA) and a) continue development of the Stock Identification Methodology; b) advise on the need for future meetings of the SIMWG, and 2000 No species reviewed By correspondence J. Waldman (USA) prepare appropriate Terms of Reference if required S. Cadrin (Co-Chair) USA, K. Friedland (Co- a) continue development of the Stock Identification Methodology; b) advise on the need for future meetings of the SIMWG, and 2001 No species reviewed By correspondence Chair) USA, J. Waldman prepare appropriate Terms of Reference if required. (Co-Chair) USA S. Cadrin (Co-Chair) USA, K. Friedland (Co- a) prepare a complete draft of the Stock Identification Methodology publication; b) advise on the need for future meetings of 2002 No species reviewed By correspondence Chair) USA, J. Waldman the SIMWG, and prepare appropriate Terms of Reference if required. (Co-Chair) USA S. Cadrin (Co-Chair) USA, K. Friedland (Co- a) prepare a complete draft of the Stock Identification Methodology publication; b) advise on the need for future meetings of 2003 No species reviewed By correspondence Chair) USA, J. Waldman the SIMWG, and prepare appropriate Terms of Reference if required. (Co-Chair) USA S. Cadrin (Co-Chair) USA, K. Friedland (Co- a) work with the publisher in producing “Stock Identification Methodology”; b) advise on the need for future meetings of the 2004 No species reviewed Chair) USA, J. Waldman SIMWG, and prepare appropriate Terms of Reference if required. By correspondence (Co-Chair) USA S. Cadrin (Co-Chair) a ) advise on the need for future meetings of the SIMWG, and prepare appropriate Terms of Reference if required; b ) liaise with 2005 USA, J. Waldman (Co- SGSIMUW on developments in stock identity studies in North Sea whiting. whiting (Merlangius merlangus) By correspondence Chair) USA

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a ) liaise with ICES working groups and study groups dealing with stock identification issues; providing technical reviews to expert groups and LRC; Specifically provide advice methods, analyses and procedures, on wide ranging shark species to WGEF, Wide ranging shark species and demersal new MoU species to WGNEW, and herring west of the British Isles to HAWG; b ) review and report on new advances in stock 2008 skates, MoU species, Herring west of the By correspondence S. Mariani (Ireland) identification methods as they develop and new results that are relevant to ICES work; c ) advise on the need for future British Isles , Redfish (Sebastes mentella) meetings of the SIMWG, and prepare appropriate Terms of Reference if required; d ) review the papers presented at Theme Session L at the 2007 ASC and make recommendations for future work. a) liaise with ICES working groups and study groups dealing with stock identification issues; provide technical reviews to expert groups and LRC; b ) review and report on new advances in stock identification methods as they develop, and also new results Deep sea fish, blue whiting (Micromesistius that are relevant to ICES work; c ) provide an updated review of available information on stock structure in elasmobranchs; d ) 2009 By correspondence S. Mariani (Ireland) poutassou), redfish (Sebastes mentella) review and report on all available multidisciplinary studies in Stock Identification, and produce a first‐draft protocol for the integration of results from multiple disciplines; e ) produce a first‐draft, practical protocol (suitable to constant updating) for Stock Identification. a ) Liaise with ICES working groups and study groups dealing with stock identification issues and provide technical reviews to these groups and SCICOM; b ) Review and report on new advances in stock identification methods as they develop, and new results that are relevant to ICES work; c ) Consider the available multidisciplinary studies in Stock Identification, and produce a first draft “SIP” (Stock Identification Protocol) for the integration of results from multiple disciplines; d ) Review the scientific resources and tools available to ICES for investigating stock structure and determining appropriate management units, including In person meeting technologies, sampling programmes, laboratories; e ) Identify limitations and gaps in the scientific capacity of ICES for 2010 Redfish (Sebastes mentella) held in Oregrund, S. Mariani (Ireland) investigating stock structure and determining appropriate management units, including technologies, sampling programmes, Sweden laboratories; f ) Consider stock identification methods used for non-fish biology (e.g. marine mammals) and whether any lessons may be learned for fish stock assessment; g ) Develop terms of references based on a work plan for the next two years, which complement the objectives of the ICES science plan; h ) Express expert advice on the NEAFC request to ICES regarding additional review of the stock structure of Sebastes mentella in the Irminger Sea and adjacent areas, with specific consideration of NEAFC documents AM 2009/23 and AM 2009/29-rev1.

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a ) Review and report on new advances in stock identification methods as they develop, as well as new results that are relevant to ICES work; b ) Provide technical reviews and expert opinions on matters of Stock Identifications, as requested by specific Deepwater stocks, Atlantic cod (Gadus In person meeting S. Mariani (United Working Groups and SCICOM; c ) Evaluate any new information relevant to the stock identity of deep-water stocks and to make 2012 morhua), plaice (Pleuronectes platessa), and held in Manchester, Kingdom) recommendations to WGDEEP on the geographical composition of stock units; d ) Consider the results of WGAGFM in terms of flounder (Platichthys flesus) UK using parasites as stock discrimination tools and comment on whether these methods can be brought to bear on contemporary stock identification issues addressed by SIMWG. a ) Recent advances in stock identification methods, with a particular emphasis on technological and conceptual progress in Turbot (Scophthalmus maximus), dab tagging approaches; b ) Reviews and advice on matters of Stock Identification, which specifically focused on the three tasks (Limanda limanda), brill (Scophthalmus In person meeting S. Mariani (United below: i ) Advice on stock structure of turbot, dab and brill in the Baltic Sea ii ) Evaluation of stock identity of anglerfish in ICES 2013 rhombus), the black anglerfish (Lophius held in Hamburg, Kingdom) and adjacent areas and proposed new methodologies for future studies iii ) Considerations on the role of genetic markers under budegassa) and the white anglerfish (Lophius Germany directional selection in stock identification analysis; c ) A systematic appraisal of the terminology used in the field of stock piscatorius) identification. a ) Review recent advances in stock identification methods; b ) Build a reference database with updated information on known biological stocks for species of ICES interest; Technical reviews and expert opinions on matters of stock identification, as Blue whiting (Micromesistius poutassou), 2014 By correspondence requested by specific Working Groups and SCICOM; c ) Develop a universal framework for consistent usage of terminology Atlantic cod (Gadus morhua) relevant to stock identification; d ) Review and report on advances in mixed stock analysis, and assess their potential role in L. Kerr (USA) improving precision of stock assessment.

Haddock (Melanogrammus aeglefinus) , a ) Review recent advances in stock identification methods ;b) Build a reference database with updated information on In person meeting anchovy (Engraulis encrasicolus), megrim known biological stocks for species of ICES interest; (B1) Technical reviews and expert opinions on matters of stock 2015 held in Portland, (Lepidorhombus whiffiagonis), plaice identification, as requested by specific Working Groups and SCICOM; c ) Review and report on advances in mixed stock Maine (USA) Pleuronectes platessa , greater silver smelt analysis, and assess their potential role in improving precision of stock assessment. (Argentina silus) L. Kerr (USA)

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Table 2 Summary table of existing species-specific reviews conducted by SIMWG on the ICES stocks (1998–2014).

Year Species ICES Stock (s) Ecoregion Requested by Haddock in ICES Subareas IV and VIa (North Sea and 2015 Haddock (Melanogrammus aeglefinus) North Sea and West of Scotland WHHAD West of Scotland) Megrim (Lepidorhombus whiffiagonis) megrim in ICES Subareas VIIIc and IXa Bay of Biscay and Iberic waters WGBIE

Anchovy (Engraulis encrasicolus) European anchovy in ICES Division IXa Bay of Biscay and Iberic waters WGHANSA

Plaice (Pleuronectes platessa) Plaice in ICES sub-area IIIa and Adjacent Areas North Sea and Baltic Sea WKPLE

Greenland and Iceland Seas, Barents Sea, Faroes, Norwegian Greater silver smelt in ICES Subareas I, II, IV, VI, VII, Sea, Celtic Sea North Sea, South Greater silver smelt (Argentina silus) ADGDEEP VIII, IX, X, XII and XIV and Divisions IIIa and Vb European Atlantic Shelf, Baltic Sea, and Oceanic northeast Atlantic

Widely distributed and 2014 Blue whiting in Subareas I–IX, XII, and XIV WGWIDE Blue whiting (Micromesistius poutassou) migratory stocks 1) Cod in inshore waters of NAFO Subarea 1 Atlantic cod (Gadus morhua) (Greenland cod), 2) Cod in offshore waters of ICES Iceland and East Greenland NWWG Subarea XIV and NAFO Subarea 1 (Greenland cod) 2013 Turbot (Scophthalmus maximus) ICES Subarea IIId Baltic Sea WKFLABA Dab (Limanda limanda) ICES Subarea IIId Baltic Sea WKFLABA Brill (Scophthalmus rhombus) ICES Subarea IIId Baltic Sea WKFLABA 1 ) The northern shelf stock consisting of Anglerfish in Division IIa (Norwegian Sea), Division IIIa (Kattegat and Skagerrak), Subarea IV (North Sea), and Subarea VI Anglerfish (Lophius budegassa) and the white anglerfish (West of Scotland and Rockall) 2 ) The northern northeast Atlantic WKFLAT (Lophius piscatorius) southern shelf stock consisting of Anglerfish in Divisions VIIb–k and VIIIa,b,d 3 ) The southern southern shelf stock consisting of Anglerfish in Divisions VIIIc and IXa ICES Subarea XIV and NAFO Subarea 1 (Greenlandic 2012 Atlantic cod (Gadus morhua) East and West Greenland NWWG cod) Plaice ICES Subarea IIIa North Sea WKPESTO Baltic flounder ICES Subarea IIId Baltic Sea WKFLABA Deepwater stocks: Roundnose grenadier (Coryphaenoides rupestris) Black scabbardfish (Aphanopus carbo) Blue Ling (Molva dypterygia) Ling (Molva molva) Widely distributed and WGDEEP Tusk (Brosme brosme) migratory stocks Greater Forkbeard (Phycis blennoides) Alfonsinos (Beryx splendens and Beryx decadactylus) Great silver smelt (Argentina silus) Black-spot red sea bream (Pagellus bogaraveo) Redfish (Sebastes mentella) 1) a ‘Deep Pelagic’ stock (ICES Vb, XII, XIV >500m), 2) a Iceland and Greenland Seas, 2011 Redfish (Sebastes mentella) ‘Shallow Pelagic’ stock (ICES Vb, XII, XIV <500m), and 3) NEAFC and ACOM Faroes an ‘Icelandic Slope’ stock (ICES Va, XIV). Sprat (Sprattus sprattus) ICES sub-areas VI and VII Celtic Sea HAWG Haddock (Melanogrammus aeglefinus) in the North Sea North Sea and west of Scotland and the West of Scotland ICES area VI (west of Scotland) and IV (North Sea) WKBENCH 1) a ‘Deep Pelagic’ stock (ICES Vb, XII, XIV >500m), 2) a Iceland and Greenland Seas, 2010 Redfish (Sebastes mentella) ‘Shallow Pelagic’ stock (ICES Vb, XII, XIV <500m), and 3) Faroes an ‘Icelandic Slope’ stock (ICES Va, XIV). NEAFC

1) a ‘Deep Pelagic’ stock (ICES Vb, XII, XIV >500m), 2) a Iceland and Greenland Seas, 2009 Redfish (Sebastes mentella) ‘Shallow Pelagic’ stock (ICES Vb, XII, XIV <500m), and 3) Faroes an ‘Icelandic Slope’ stock (ICES Va, XIV). WKREDS Blue whiting (Micromesistius poutassou) ICES Subareas I–IX, XII, and XIV Widely distributed and migratory ACOM Deep sea fish General comments across ICES areas. Across ICES ecoregions WGDEEP

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1) Western Icelandic shelf, 2) Deep Irminger Sea and Western Faroe, 3) all other localities comprised Iceland and Greenland Seas, 2008 Redfish (Sebastes mentella) between the shallow Irminger Sea off Newfoundland Faroes, Norwegian and Barrents SGRS all the way to the Barents Sea and the offshore Seas Northern Norwegian waters (“shallow stock”). Herring west of the British Isles ICES Area VIaN, VIaS, VIIc, VIIb, VIIk, VIIj, VIIg, VIIh, VIIaS Celtic Seas HAWG

New MoU species (sea bass, striped red mullet , red, tun and gray gurnards, flounder, witch flounder, brill, turbot, General comments across ICES areas. Across ICES ecoregions WGNEW lemon sole, dab)

Wide ranging shark species and demersal skates General comments across ICES areas. Across ICES ecoregions WGEF

Deepwater stocks: Tusk (Brosme brosme) ICES Area I,II, Va, Vb, IV, VIa, VIb Blue ling (Molva dypterygia) ICES Area Va, Vb, VIa Ling (Molva molva) ICES Area II, Va, Vb, IV, VI Widely distributed and 2007 WGDEEP greater argentine (Argentina silus) ICES Area IIIa, Va,Vb,VII migratory stocks roundnose grenadier (Coryphaenoides rupestris) MAR, ICES Area VIb2, XIIb blackscabbardfish (Aphanopus carbo) ICES Area VIa, IX red seabream (Pagellus bogaraveo) ICES Area IX, X Redfish (Sebastes mentella) ICES Areas Va, Vb, and XIV, V, VI, XII, and XIV, Iceland and East Greenland AFWG and NWWG 2006 No species reviewed NA NA NA

2005 Whiting (Merlangius merlangus) ICES Subarea IV and Division VIId North Sea SGSIMUW

2004 2003 2002 2001 No species reviewed NA NA NA 2000 1999 1998 1997

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Annex 5: Evaluation of Greater Silver Smelt Stock Identity in ICES Subareas I, II, IV, VI, VII, VIII, IX, X, XII and XIV and Divisions IIIa and Vb

ECOREGIONS: Greenland and Iceland Seas, Barents Sea, Faroes, Norwegian Sea, Celtic Sea North Sea, South European Atlantic Shelf, Baltic Sea, and Oceanic northeast Atlantic

ICES STOCK(S): There are currently two ICES stocks for greater silver smelt: 1. Greater silver smelt in Division Va (Iceland) 2. Greater silver smelt in subareas I, II, IV, VI, VII, VIII, IX, X, XII, and XIV, and Divisions IIIa and Vb (other areas). SIMWG FINDINGS: SIMWG does not find strong scientific evidence in the working document provided by WGDEEP to support the proposed revision of greater silver smelt stock units. Furthermore, SIMWG does not find strong biological support for the current stock units for greater silver smelt and suggests that these should be reviewed critically for their appropriateness. SIMWG strongly recommends future stock identity work be conducted to examine the population structure of greater silver smelt. This is a data poor species and in the absence of information, SIMWG recommends that the current stock structure stand and that stock identification work on this species be prioritized.

Background SIMWG was asked in April 2014 to contribute to the Advice Drafting Group on Deep Sea Stocks (ADGDEEP) by providing feedback on issues of stock identity of greater silver smelt (Argentina silus) in ICES Subareas I, II, IV, VI, VII, VIII, IX, X, XII and XIV and Divi- sions IIIa and Vb. SIMWG was specifically requested to review and provide comments on a working document (ICES WGDEEP 2014 WD) presented during the 2014 WGDEEP meeting. In the 2014 WD, WGDEEP proposed a change to the management units of greater silver smelt from the current two stock units to a proposed four stock unit:

Current ICES stock units: 1. Greater silver smelt in ICES division Va (Iceland) 2. Greater silver smelt in ICES, and Divisions IIIa and Vb (other areas).

Proposed revision to ICES stock units: 1. Greater silver smelt in ICES division Va and XIV 2. Greater silver smelt in ICES division Vb and VIa 3. Greater silver smelt in ICES division IIb 4. Greater silver smelt in all other areas where the species occurs (IIIa, IV, VIb, VII, VIII and XII).

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SIMWG Review of WGDEEP Working Document The initial distinction between the current two ICES stocks for greater silver smelt was the result of recommendations made by SGDEEP in 1998. This distinction was based on a review of available stock identity information at the time. The separation of Division Va as a distinct stock appears to be based on results of Icelandic life history studies, however, no information from this study was provided within the WD for review. In 2007, WGDEEP and SIMWG met to evaluate the available stock identity information for deepwater species, including greater silver smelt. At that time, a literature review was conducted and the conclusion of this joint workshop on greater silver smelt was that: “Available information is not sufficient to suggest changes to current ICES interpretation of stock structure. In order to evaluate the stock structure further, sampling for genetic studies from the whole distribution area of great silver smelt is needed. It is therefore recommended that such work should be initiated as soon as possible”. To date, this recommendation has not been acted on and genetic methods have not been applied for stock identification of greater silver smelt. In 2012, SIMWG reviewed the state of knowledge on greater silver smelt population structure again. At the time SIMWG concluded: “Hardly anything is known about the population structure of Argentina silus. Only basic biological parameters have been examined, in Ice- land (Magnusson, 1994) and Skagerrak (Bergstad, 1993), suggesting possibly later maturation in Icelandic waters than in the Skagerrak and NE North Sea. This is nevertheless grossly insufficient to make any form of inference on stock structure. Given the substantial and increasing landings of A. silus, it would be of utmost importance to conduct a rigorous study of stock structure in this species. Given the lack of knowledge, SIMWG cannot find a biologically reasonable justification for the current state of the assessment, which considers two units: Iceland vs. ‘Everything else’.” A web search (ASFA) for recent literature relevant to stock identification published on greater silver smelt since 2012 did not reveal any new publications on this species in the peer-reviewed literature.

In 2013 ACOM provided advice to WGDEEP that “greater silver smelt may be sufficiently isolated at separate fishing grounds to be considered as individual assessment units”. In subse- quent clarification of this advice to WGDEEP ACOM stated “The ICES approach to DLS recognises that it is possible to give advice in data limited situations. A similar approach could be extended to cover the definition of advice units where data is limited and it is unlikely that conclusive evidence on stock identity will be available in the near future”. Based on this advice, WGDEEP recommended that fishing areas be used to define stock units for greater silver smelt.

The WD provided to SIMWG described the current fishing areas for greater silver smelt, documenting three regions from which the majority of landings are taken: 1) around Ice- land (Va and XIV), 2) to the west of Norway (II), and 3) around the Faroes, Whyville- Thomson Ridge and Northern Rockall Trough region (Vb and VIa). Information on the magnitude of landings by ICES subdivisions was presented in the WD; however, no information was presented regarding the timing of catches. This is a serious weakness as the potential exists that there is a single spawning area with aggregation forming inde- pendently outside the spawning season. In recognition that analysis of landings data can be used as a proxy for trends in the abundance of fish across regions and coherence in trends in abundance suggest similar

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dynamics across regions, SIMWG explored the correspondence in trends in landings by area. It is important to note, however. that there are many caveats to this approach as the trends in landing can be determined by regulation, effort, markets, etc. An examination of the correlation in landings across the five primary regions in which greater silver smelt are landed revealed positive correlations between landings in II, Va, Vb, and VIa, with the strongest positive relationship between landings in Va (Iceland) and Vb (Faroes; Ta- ble 1). Landings in III_IV were negatively correlated with the other regions. This analysis would suggest that separation of regions II, Va, Vb, and VIa is not appropriate, although a more detailed analysis would be required to draw conclusions.

Table 1. Pearson correlation coefficients between landings of greater silver smelt across ICES areas. Bolded coefficient highlight positive correlations.

II III_IV Va Vb VIa II 1 -0.15 0.24 0.31 0.36 III_IV 1 -0.31 -0.24 -0.38 Va 1 0.78 0.38 Vb 1 0.32 Via 1 Additionally, a principal components analysis (PCA) of landings data in regions II, III_IV, Va, Vb, and VIa was carried out to identify patterns in regional landings. PC 1 and PC 2 explained 68% of the overall variance. The PCA revealed two groupings based on landings data from 1988 to 2013: 1) landings in regions III-IV (North Sea), which show oscillating catches but no long term trend, and 2) landings in regions II, Va, Vb, and VIa (Iceland, Faroes, Norwegian Sea), which show a general increase in landings over the time period of the landings records (Figure 1).

Figure 1. Greater silver smelt landings in tonnes in ICES areas II, III_IV, Va,Vb, and VIa.

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Conclusions and Recommendations SIMWG finds the support for the proposed revision to ICES stock units for greater silver smelt to be weak. Our criticism can be summarized in the following points:

• There is very little biological information available on stock identity of greater silver smelt and no new information was presented in the WD since SIMWG’s previous reviews greater silver smelt in 2007 and 2012. There is no evidence that indicates genetic or phenotypic differences between groups of fish in the revised stock units. • In the absence of information, WGDEEP contends that the distribution of the fishery can be used to define stock units for this species. Although there are examples of the application of this type of “harvest stock” approach to define management units, the weakness in this analysis is that the temporal aspect of the fisheries is not explicitly considered. Furthermore the analysis of trends in the landings data by SIMWG does not support the revised stock units. • This proposed revision seems to go against normal procedures at ICES to leave stock definitions unchanged unless there is reliable scientific evidence that they should be altered.

References

ICES. 2007. Report of the Working Group on the Biology and Assessment of Deep-Sea Fisheries Resources (WGDEEP), 8 - 15 May 2007, ICES Headquarters. ICES CM 2007/ACFM:20.478 pp.

ICES. 2012. Report of the Stock Identification Methods Working Group (SIMWG), 14 - 16 May 2012, Manchester, UK. ICES CM 2012/SSGSUE:04. 48 pp.

ICES WGDEEP 2014 WD: Revision of ICES assessment units for greater silver smelt based on the distribution of fishing grounds

List of participants by correspondence Name Email Lisa Kerr (Chair) [email protected] Stefano Mariani [email protected] David Secor [email protected] Ann-Britt Florin [email protected]

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Annex 6: Evaluation of Plaice Stock Identity in ICES sub-area IIIa and Adjacent Areas

ECOREGION: North Sea and Baltic Sea

ICES STOCK(S): Plaice in Subdivisions 24-32 (Baltic Sea), plaice in Subdivisions 21–23 (Kattegat, Belts, and Sound); and plaice in Subdivision 20 (Skagerrak).

SIMWG FINDINGS: The perception of plaice in Subdivisions 21-32 as a single‐stock unit is not well supported by the best available science. SIMWG’s review supports the stock separation between plaice in SD 21-23 and SD 24-32. This conclusion is supported by genetic analysis and tagging data, as well as modelled egg and larval distributions, and growth characteristics. A combination of tagging, growth, and genetic information suggest that Skagerrak (SD 20) and Kattegat (SD 21) should continue be assessed and managed separately. Based on the current information available, the sub-dividing of the Skagerrak and Kattegat into western and eastern parts is not well supported. Conse- quently, we find there is a valid scientific basis to support the current ICES stock units for plaice in the region. SIMWG strongly recommends future work examining the mixed stock composition of fish in the transition region (Skagerrak, Kattegat).

Background

SIMWG (2014) was recently asked to contribute to the Benchmark Workshop on Plaice stocks (WKPLE) by providing feedback on issues of stock identity of plaice in Subdivi- sions (SD) 20-32. SIMWG was specifically requested to review two working documents (WD) for WKPLE:

WD 1: Sven Stötera, Rainer Oeberst, Uwe Krumme: Information on distribution, survey indices, maturity, growth patterns and egg buoyancy for plaice Pleuronectes platessa in the Baltic Sea (SD22-32) and its implication for a separation of two Baltic plaice stocks.

WD 2: Clara Ulrich, Jesper Boje, Karin Hüssy, Asbjørn Christensen, Henrik Degel, Lotte Worsøe Clausen, Jakob Hemmer-Hansen: Summary of results and preliminary conclusions from a Danish project on plaice (Pleuronectes platessa) stock structure in the transition area between the North Sea and the Baltic Sea.

In 2012, WKPESTO (ICES 2012) proposed a change to the management units of plaice in IIIa and the western Baltic as follows: 1. Plaice in Skagerrak (SD 20), which is closely associated with the North Sea, should be assessed with the North Sea stock but managed separately in order to preserve the local spawning populations 2. Plaice in Kattegat (SD 21), the Belts (SD 22) and the Sound (SD 23) should be assessed as one stock but managed separately to maintain local populations 3. Plaice from SD 24 to SD 32 should be assessed and managed as one stock.

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In 2012 SIMWG agreed that these conclusions were generally supported by the information considered by WKPESTO, but indicated that the information was not complete. SIMWG recommended a more comprehensive review of all information available on stock identity of plaice in IIIa as well as adjacent areas.

SIMWG Review of WKPLE Documents

The main focus of WD 1 was an examination of the stock division between SD 21-23 and SD 24-32. The validity of this stock division was firmly criticized both from a biological point view and from a managerial point of view. This criticism can be summarized in following points:

• There was very little information given in the WKPESTO (ICES 2012) report on the rationale for splitting plaice in SD 22 and 23 from the rest of the western Bal- tic (SD 24) and eastern Baltic (SD 25-32). • WD1 suggested that the primary rational for splitting was driven by the idea that splitting was a more precautionary approach to plaice management given that work on herring had shown assessment of metapopulations could fail to detect overexploitation. The authors suggest that this assumption is unsubstantiated for plaice and that splitting the stock departed from normal procedures at ICES to leave stock definitions unchanged unless there is reliable scientific evidence that they should be altered. • The authors also cite concern about the risk that the data poor stock of plaice in SD 24-32 may act a choke stock for other fisheries, especially the cod fishery, in the area. The criticism of WKPESTO’s conclusions concerning the division between SD 21-23 and SD 24-32 is followed up the authors’ review of data available on plaice from the Fish- frame, InterCatch and DATRAS databases. They review information on the spatial distribution, year class strength variations, length-weight relationships, age-length relationships, landings, maturity and spawning cycles of plaice. The review focuses on whether the plaice in the two current stock areas exhibit similarity in trends and biological characteristics. Analysis of the spatial distribution of plaice based on trawl survey data indicates that large plaice are unevenly distributed in the first quarter (i.e. the spawning period) suggesting the presence of unique spawning aggregation in SD 21-22 as well as SD 24-25, albeit at lower magnitude. SIMWG noted the presence of independent spawning aggregations in both areas is a first prerequisite for stock separation. The authors noted similarity in trends in relative spawning stock biomass in the two areas over time (although no statistical analysis was conducted to evaluate the strength of the correlation), however, the two areas do not appear to exhibit the same pattern before 2010. An analysis of weight at length indicated that plaice in SD 24 were heavier than plaice in SD 22. Howev- er, examination of growth curves for fish in SD 22 and 24 identified no significant differences. Egg density potentials of Baltic plaice did not differ between SD 22, 24, 25, 26, and 28. A comparison of maturity ogives across areas suggested plaice in SD 21 may have a slightly lower length L50 (length-at-maturity where >50% of females are considered to be mature) than plaice in SD22/23 and eastwards, however, there was not any statistical treatment of the data (e.g. by applying generalized linear models with link function).

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Overall SIMWG felt the review of the data presented in the review did not unambiguous- ly resolve the issue of stock identity for plaice in SD 21-32. The authors of WD1 make this point themselves. However, they also contend that several pieces of information do not support separation of plaice between SD 21-13 and SD 24-32 and given these findings conclude that the one stock hypothesis is the most appropriate. SIMWG notes that the specific indicators of stock identity evaluated in the study are considered rather weak and are seldom conclusive to the extent genetic data or another more direct measure of stock identity might be (e.g. tagging data). Many questions raised in WD1 are directly addressed with additional data in WD2. WD2 provides a summary of stock identification information related to plaice in IIIa and adjacent areas. This review includes information on modelled egg and larval distributions, growth characteristics, adult migration based on tagging data, and genetics. Modelled Egg and Larval Distributions Egg and larval drift were analysed in a 3D individual-based model framework with the goal of resolving the general transport patterns of propagules spawned in Katte- gat/Skagerrak and the North Sea. The results of model simulations indicate that low levels of propagules from major plaice spawning grounds in the North Sea are dispersed into the Skagerrak-Kattegat. However, if spawning intensity in the North Seas were higher, the drift of propagules from this region could have a significant impact on dynamics in the Skagerrak-Kattegat. SIMWG found modelled egg and larval distributions and information on connectivity supported the assessment of plaice in Skagerrak (SD 20) with the North Sea stock. Growth Characteristics Analysis of plaice growth was based on otolith measurements of annual growth bands and back-calculation of growth rate. The analysis indicated that there was no growth differentiation detected within the Kattegat or Skagerrak, whereas there were significant growth differences between the two areas supporting their separation. There were no significant differences in growth between SD 24 and 25 (providing support for their grouping), however, there were distinctive patterns in between growth of fish in SD 24- 25 and SD 22, providing some support for separation of these areas. This is the opposite of what was concluded regarding growth characteristics of plaice from these two areas in WD1. No significant differences were found between the eastern and western areas within Kattegat and Skagerrak respectively. Tagging Data Data from previous tagging experiments on plaice conducted from 1903-1964 were reviewed to evaluate the location of recaptures and degree of residency within the North Sea, Skagerrak West, Skagerrak East, the Belts (SD 21-23), and Baltic (24-25). The synthesis of recapture data revealed a high degree of residence in all areas (87-99%), except in Skagerrak East, from which tagged fish moved either to the Kattegat or the North Sea. Tagged fish in Skagerrak W. exhibited low levels of connectivity with fish in the North Sea and vice versa. Plaice tagged in the Kattegat, the Belts, and the Baltic exhibited a high degree of residency. An examination of recapture data for juvenile fish showed residency within each of the four release locations during this life stage. The review recognized shortcomings of the data, including that they come from past period in which the

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biological regime might differ and the unbalanced nature of the data. SIMWG noted that overall, the high degree of residency of plaice observed in SD 21-23 and SD 24-32 supports the separation of these areas and the high connectivity between plaice in Skagerrak and the North Sea supports the grouping of these regions together. Tagging suggests Skagerrak is an area of stock mixing. Genetics Analysis The genetic structure of plaice (collected in North Sea, Skagerrak West, Skagerrak, Katte- gat, Baltic W., and Baltic E) was investigated by analysis of over 5600 SNPs. The analysis shows significant genetic differentiation across all groups, with differentiation increasing with geographic distance from the North Sea over the transition zone (Skagerrak, Katte- gat) to the Baltic (Figure 1). Fish collected in the transition zone (Skagerrak, Kattegat) were composed of a mixture of local fish and fish from the Baltic and North Sea. It was estimated that nearly 50% of fish in the Skagerrak may have originated from the North Sea. Samples from Kattegat showed high representation of fish originating from the Bal- tic. Overall results provide evidence of population structure, as well as evidence of mixing, particularly within the transition zone. On the question of population integrity, WD2 assumes that the population structure is preserved in spite of high degree of mechanical mixing of individuals by natal homing. The strongest genetic differentiation was identified between fish in the Baltic (W and E) and fish in the Skagerrak and North Sea.

Figure 1 (Figure 15 from WD2) Multidimensional scaling plot of pairwise estimates of population differentiation (FST; Weir and Cockerham, 1984).

Synthesis of Stock Identity Information In conclusion, WD2 filled in many of the gaps in knowledge that were present in the WKPESTO (2012) document. SIMWG felt this document presented a rigorous and holistic view of the best available science related to stock structure of plaice. The review group found that the stock separation of plaice in SD 21-23 and SD 24-32 was firmly supported by the information reviewed in WD2. The data show that Skagerrak and Kattegat is a region of mixing of biological populations. The division between Skagerrak W and Skag- errak E, and between Kattegat W and Kattegat E, respectively, are questionable regarding

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the findings presented in WD2. Stock composition analysis will likely be needed in this region to resolve origin of fish due to the mixed stock composition.

Conclusions and Recommendations SIMWG finds the assertions in WD1, that there is no stock separation between SD 21-23 and SD 24-32, to not be well supported by the best available science. SIMWG considers there to be evidence, as presented in WD2, from genetic analysis and tagging data, as well as modelled egg and larval distributions, and growth characteristics (although here the two reports differ), to support stock separation between plaice in SD 21-23 and SD 24- 32. Tagging suggested limited connectivity between plaice in the Baltic and the transition zone, with fish in both areas exhibiting a high degree of residency. The conclusions drawn from analysis of growth characteristics differed between WD1 and WD 2. WD 1 found no significant difference in growth curves between SD 22 and 24, however there was evidence that plaice in SD 24 were heavier at length than plaice in SD 22. Growth analysis in WD2 showed no difference between fish in SD 24 and 25 (supporting their grouping), but did find significant differences between Baltic (SD 24-25) and transition zone fish (SD 21-22). Genetic data suggest limited differentiation between plaice in SD 24 and SD 25 (supporting their grouping), and stronger differentiation between plaice in SD 21 and 25. Genetic data also indicated mixing between Baltic and transition zone populations, which was particularly evident in the Kattegat sample (which appeared to be composed of local population and Baltic fish) resulting in weak differentiation between SD 21 and 24 samples). Based on evidence of mixed stock composition in the Kattegat SIMWG strongly recommends future work examining the origin of fish in this region. The combination of tagging information indicating limited adult migration between Skagerrak and Kattegat and the presence of significantly differentiated (but weak) genetic samples, as well as supporting information from growth analyses in WD2 suggest that Skagerrak (SD 20) and Kattegat (SD 21) should continue be assessed and managed separately. At this time, the sub-dividing of the Skagerrak and Kattegat into western and eastern parts by WKPESTO is not well supported, given the information presented in WD2. There is some evidence that local stocks may exist on the Swedish Skagerrak and Kattegat coasts, however, further work is needed to resolve this. Based on evidence of mixing within the transition zone SIMWG strongly recommends future work examining the mixed stock composition of fish in this region. We support the recommendation made in WD2 to pursue the approach currently applied in the herring assessments in IIIa in which stock identification work allows for proportions of fish to be allocated to known biological populations.

References

ICES. 2012. Report of the Workshop on the Evaluation of Plaice Stocks (WKPESTO). ICES CM 2012/ACOM:32.

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List of participants by correspondence Name Email Ann-Britt Florin [email protected] Lisa Kerr (Chair) [email protected] Henrik Svedäng [email protected]

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Annex 7: Evaluation of Haddock Stock Identity in ICES Subareas IV and VIa (North Sea and West of Scotland)

ECOREGIONS: North Sea and West of Scotland

ICES STOCK(S): Haddock in ICES Subarea IV and VIa (North Sea and West of Scotland)

SIMWG FINDINGS: SIMWG finds strong scientific evidence in the working document provided by WKHAD to support the current combined stock unit for haddock in Subarea IV and VIa (North Sea and West of Scotland). SIMWG finds there is some indication of a unique stock in the Clyde; however, more supporting evidence would be needed to recommend a change to the stock units. While a spatially explicit model of haddock in this region could inform finer scale management, there is not sufficient data at this time to implement this approach. SIMWG recommends that the current stock structure stand. Background

Until 2014, haddock in Subarea IV and Divisions IIIa and VIa (North Sea, Skagerrak, and West of Scotland) were assessed as two separate stocks. The 2014 Benchmark Workshop for Northern Haddock Stocks (WKHAD 2014) concluded that the two haddock stocks should be assessed as one stock.

SIMWG was asked by WKHAD for feedback on issues of stock identity of haddock (Mel- anogrammus aeglefinus) in ICES Subareas IV and VIa. SIMWG was specifically requested to review and provide comments on a working document (Wright et al. 2014) presented during the 2014 ICES benchmark assessment on haddock. WKHAD asked SIMWG to review the document and address the following issues of concern: a) Should haddock in the North Sea and West of Scotland areas be combined into a single assessment unit? b) Is there support for the Clyde area to be excluded from estimates of abundance of haddock in division VIa and assessed as a distinct stock? c) What is the possibility of assessing haddock using a spatially explicit model and what data gaps exist? Genetics The Working Document describes population genetic data based on microsatellite genotyping of eight samples from some of the main haddock areas of interest. The study was conducted using 6 loci (one was discarded due to the potential influence of null alleles) of medium-high diversity and yielded a pattern of remarkable genetic homogeneity across areas. Pairwise comparisons returned some statistically significant values; however, with the exception of a comparison between the Irish Sea and the Dogger bank, these values were not consistent across methods (exact-tests and FST analogues). The probability values do not appear to have undergone correction for multiple testing and with point estimates <0.003, they are likely to be below the threshold of power afforded by a suite of 6 loci. In combination with the fact that the samples represent single points in time (without replication), collective evidence suggests that there is no basis to consider any of the screened collections biologically different from a neutral genetic point of view. The Ice-

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landic samples appear slightly divergent if plotted using a Multidimensional Scaling and it is fair to assume that they represent distinct biological units, but there is not strong support for the claim of reduced effective population size (Waples & Do, 2008) and con- sequent random genetic drift in the Irish Sea. The lack of samples from the Clyde area prevent any speculation regarding potentially isolated fjord/inshore unit. While such units have been demonstrated to exist, for instance, in Atlantic cod (Knutsen et al., 2011), it would take a substantial, targeted effort, with replicated temporal samples, to test this hypothesis. While SIMWG welcomed the generation of a full, recent, population genetic data set on haddock (which had long been overlooked by the international community of molecular ecologists), we find that genetic data, so far, do not justify any splitting of assessment and management units for haddock on European continental shelves. Early Life history stages The waters west of Scotland and the North Sea and are a highly advective environment and the residual currents in this region could conceivably lead to substantial transport of eggs and larvae from haddock spawning grounds west of Scotland to nursery grounds in the North Sea. Furthermore, the relatively long incubation time and duration of the pelagic larval phase for haddock in the region indicates there is the potential for extensive dispersal of early life stages. The rather continuous distribution of eggs observed in ichthyoplankton surveys north the British Isles suggests that the shelf edge current exerts a strong influence on larval dispersal in the region. An early individual-based modelling experiment (Heath and Gallego, 1997) indicated the potential for transport of early life stages from spawning grounds on the west of Scotland eastward into the North Sea. Model results also indicated the potential for dispersal barriers to arise between the northern and southern portions of the North Sea. While the model results are informative, the hydrodynamic model had relatively coarse horizontal resolution (~18 km) and relied upon the use of mean climatological conditions to derive the velocity fields. There- fore, the results from this study are likely not reliable enough to inform the connectivity rates needed for a spatially-explicit assessment. Given the vast advancements in oceanographic models and coupled biophysical models that have occurred in recent years, a contemporary IBM study that builds off earlier work done by Heath and Gallego (1997) may be particularly informative for this stock. Otolith Chemistry An otolith microchemistry study conducted by Wright et al. (2010) suggested the potential for a particular nursery region, the Eastern Coast of Scotland, to spill over into other broad regions in the North Sea. With adult retention in spawning regions, regional exploitation could curtail development of strong year-classes in broad regions. Although this is a cogent argument, supporting source sink-dynamics will require substantial more development of otolith microchemistry (or other natural tag approaches). The application developed in Wright et al. (2010) was a strong demonstration project but to apply this at a level to evaluate the hypothesis that local production was responsible for more global strong-year classes would require substantially more sampling of baseline conditions and better development of baselines respective of likely chemical oceanographic differences with nursery areas. Incorporation of stable isotopes and laser ablation approaches are worth pursuing in the future, but a strong challenge will be to representa-

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tively sample nurseries across broad regions and establishing year-specific otolith chemistry baselines. Otolith microstructural approaches (e.g. Brophy et al. 2006, McQuinn et al. 1997) might offer greater inter-annual stability and could be pursued. The otolith microchemistry of age-0 haddock in the Firth of Clyde was consistent with the local nursery area. Tagging The available tagging data suggests that there is very little exchange of adult haddock between the North Sea and ICES Division VIa. There appear to be at least four different groups that are relatively sedentary, including two groups within Division VIa (Firth of Clyde and northern region) and two groups in the North Sea (inshore and offshore; Fig- ure 4 from Wright et al., 2014). However, these data are from 1958 to 1983 and include a limited number of recaptures (n = 420). It was speculated that the apparent small home ranges of adults could be the result of social cohesion, while natal fidelity and the return of juveniles that were transported out of the area was also a possibility (Wright et al., 2014). No reference was provided for this tagging study, thus prohibiting closer examination of these data (e.g., time at liberty, homing behaviour). In order to permit further investigation into haddock stock structure for application to stock identification, additional research on adult movements is recommended using both conventional tagging and electronic tagging methods.

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Recruitment Synchrony of Haddock among ICES Advisory Units Haddock stocks have characteristic recruitment patterns in which occasional, strong year classes dominate the stock and fishery. Therefore, haddock is a good candidate for exploring synchronous recruitment patterns among putative stock areas. Ideally, recruitment synchrony would be tested using spatially explicit survey data, so that putative stock hypotheses are not constrained by previous assessment unit decisions. In lieu of survey data, SIMWG examined recruitment estimates for all ICES advisory units in 2014

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(ICES 2014), as well as the disaggregated recruitment estimates for the North Sea– Skagerrak (IV, IIIa) and West of Scotland (IVa) in 2013 (ICES 2013). Based on the skewed nature of haddock recruitment, estimates were Ln transformed. Year-classes were assigned to recruitment estimates based on the age of recruitment estimates, which varied among stocks. For plotting purposes, Ln recruitment estimates were standardized to the mean and standard deviation for a common period (1993–2011 year-classes). Synchrony was tested using Pearson correlation coefficients. Correlation was significantly positive (r=0.76) between Ln recruitment estimates from North Sea–Skagerrak (IV,IIIa) and West of Scotland (IVa) (Figure 1). Several year-classes (1979, 1983, 1986, 1999, 2005, 2009) were strong in both areas.

Figure 1. Recruitment synchrony of haddock in the North Sea and West of Scotland (Data derived from ICES 2013).

By contrast, there were no strong correlations among other haddock advisory units. The strongest correlations were negative, and moderately positive correlations were among non-adjacent stocks (Table 1, Figure 2). This analysis supports the decision to combine North Sea and west of Scotland haddock.

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Table 1. Correlation among Ln recruitment estimates from ICES advisory units (data derived from ICES 2014).

I,II Va Vb VIb VIIb-k VIIa IV,IIIa,VIa Arctic Icelandic Faroe Rockall CeltWScot Irish Sea North Sea Arctic 1.00 Icelandic 0.24 1.00 Faroe -0.07 0.22 1.00 Rockall -0.11 0.33 0.38 1.00 CelticWScotland 0.20 -0.32 -0.46 -0.35 1.00 Irish Sea 0.58 -0.06 -0.07 -0.38 0.34 1.00 North Sea -0.33 -0.07 0.32 0.51 -0.60 -0.34 1.00

Figure 2. Recruitment estimates of haddock for ICES advisory units (data derived from ICES 2014).

Haddock in the Firth of Clyde Haddock in the Firth of Clyde region are singled out as a potentially discrete stock from the rest of the ICES subdivisions reviewed. There is good evidence to support a discrete spawning group of adult haddock in the Clyde region based on localized tag returns. Nonetheless, limited movements of tagged haddock was noted for all tagging areas, moreover, the lack of specifics about tagging made these data difficult to interpret. Oto- lith microchemistry data also suggest that juveniles recruit locally. However, no data regarding earlier life stages was presented for the Firth of Clyde, as this region was not included in the ichthyoplankton surveys reviewed. Similarly, the genetic pair-wise comparisons do not include samples from the Clyde region. While the potential for local recruitment and small adult home ranges is suggestive, it is not compelling to assess the

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Clyde region separately from VIa. More study appears necessary to understand the inde- pendence of the Firth of Clyde and how separating it would aid in management of haddock in this region. Spatially explicit assessment model SIMWG was also asked by WKHAD to comment on the question of whether a spatially explicit assessment model would be appropriate rather than definition of either separate stocks or a spatially homogeneous stock. The benefit of a spatially explicit model is that it could enable conservation of the existing diversity of haddock spawning components in the region and thus conserve the potential for strong year classes. This approach would enable finer-scale management advice that would enable conservation of the spawning stock biomass of unique spawning components through implementation of separate TACs across areas. Spatially explicit models are limited in their application for providing catch advice due to the increased data requirements and model complexity associated with the approach. Although the group thought there was value in pursuing this approach, SIMWG had serious concerns regarding data availability with respect to implementation of spatially explicit modelling of haddock in this region. A spatial model would need to account for interchange between areas which does not seem currently feasible with the data available. It was unclear to the group whether survey data was available to support this finer- scale approach and whether catches could be attributed at a finer spatial scale as to support this approach. The available results could provide an indication of exchange for some specific years. However, further work would be needed to improve information on the exchange of fish between areas, including: 1) improve egg and larvae biophysical modelling of advection and dispersal with the latest sea circulation models, 2) conduct additional otolith microchemistry work to verify biophysical model output, 3) provide confirmation of the otolith study in the Wright et al., 2010 through analysis of additional year-classes, and 4) conduct more tagging work (most was obtained before 1980) using conventional and electronic tags.

Conclusions and Recommendations SIMWG finds strong scientific evidence in the working document provided by WKHAD to support the current combined stock unit for haddock in Subarea IV and VIa (North Sea and West of Scotland). The document provides evidence of broad dispersal of haddock during their early life history and limited dispersal as adults. There is a high degree of recruitment synchrony between North Sea and W. Scotland and genetic and otolith chemistry analyses do not justify any splitting of the current assessment and management units for haddock. SIMWG finds there is some indication of a unique stock in the Clyde based on otolith chemistry and tagging data, however, more supporting evidence would be needed to recommend a change in the stock units. While SIMWG supports development of a spatially explicit model for haddock, as this could inform finer scale management and enable conservation of the diverse spawning components of haddock in the region, there is not sufficient data at this time to implement this approach. SIMWG recommends that the current stock structure stand and future work be conducted to fully evaluate the stock identity of haddock in the Clyde and to explore the potential for developing a spatially explicit model of haddock in this region.

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References

Brophy, D., B. S. Danilowicz, and P. A. King. 2006. Spawning season fidelity in sympatric populations of Atlantic herring (Clupea harengus). Canadian Journal of Fisheries and Aquatic Sciences 63(3):607-616.

Heath M., Gallego, A. 1997. From the biology of the individual to the dynamics of the population: bridging the gap in fish early life stages. J Fish Biol (Suppl. A): 1-29

ICES. 2013. Report of the ICES Advisory Committee 2013. ICES Advice, 2013. Books 1-11.

ICES. 2014. Report of the ICES Advisory Committee 2014. ICES Advice, 2014. Books 1-11.

Knutsen, H., E.M. Olsen, P.E. Jorde, S.H. Espeland, C. Andre´ & N.C. Stenseth. 2001. Are low but statistically significant levels of genetic differentiation in marine fishes ‘biologically meaning- ful’? A case study of coastal Atlantic cod. Molecular Ecology, 20, 768–783.

McQuinn, I. H. 1997b. Year-class twinning in sympatric seasonal spawning populations of Atlantic herring, Clupea harengus. Fishery Bulletin 95(1):126-136.

Waples, R.S., and C. Do. 2008. LDNE: a program for estimating effective population size from data on linkage disequilibrium. Molecular Ecology Resources, 8: 753-756.

Wright, P. J., Tobin, D., Gibb, F. M., and Gibb, I. M. 2010. Assessing nursery contribution to recruitment: relevance of closed areas to haddock Melanogrammus aeglefinus. Marine Ecology Progress Series, 400: 221-232.

Wright, P.J., O’Sullivan, M., Holmes, S.J. and Gibb, F.M. 2014. Population structuring in haddock in the North Sea and west of Scotland. Working document to ICES benchmark on haddock 2014.

LIST OF PARTICIPANTS Name Email Steve Cadrin [email protected] Greg Decelles [email protected] Lisa Kerr (Chair) [email protected] Stefano Mariani [email protected] Richard McBride [email protected] David Secor [email protected] Christoph Stransky [email protected] Doug Zemeckis [email protected]

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Annex 8: Evaluation of European Anchovy Stock Identity in ICES Division IXa

ECOREGIONS: Bay of Biscay and Iberic waters

ICES STOCK(S): Two stock units: 1) Bay of Biscay (ICES Sub-area VIII), and 2) ICES Divi- sion IXa (Portuguese coast and Spanish waters of the Gulf of Cadiz)

SIMWG FINDINGS: SIMWG does not find sufficient scientific evidence in the working document provided by WGHANSA to support changing the current stock unit for anchovy in ICES Division IXa (Bay of Biscay and Iberic waters) at this time. SIMWG recommends that the current stock structure stand and recommends the continued approach of employing spatially explicit management and monitoring of this subdivision. SIMWG contends that splitting out biological stock units would require further research to understand the source of fish off the coast of Portugal and Galicia (local sustaining populations versus spillover from adjacent populations).

Background SIMWG was asked in 2014 by the Working Group on Southern Horse Mackerel, Ancho- vy, and Sardine (WGHANSA) to provide feedback on issues of stock identity of Europe- an anchovy (Engraulis encrasicolus) in ICES Divisions IXa. SIMWG was specifically requested to review and provide comments on a working document (Ramos 2015) pre- pared by WGHANSA. WGHANSA recommended investigation of possible separate stock identity for anchovy in IXa to be carried out by the Stock Identification Methods Working Group (SIMWG). WGHANSA recommended providing advice for the IXa south populations separate from the rest of the division. In the 2015 WD, WGHANSA proposed a revision to the management units of European anchovy from the current single unit stock in ICES Division IXa to a proposed two stock unit:

Current ICES stock units: 1. European anchovy in ICES Division IXa

Proposed revision to ICES stock units: 2. European anchovy in ICES Subdivision IXa South 3. European anchovy in ICES Subdivision IXa North, North Central, South Central Spatial Distribution Based on information from acoustic surveys, there appears to be a resident population of anchovy located in the Bay of Cadiz (ICES Subdivision IXa South). The distribution of anchovy eggs in the Bay of Cadiz is very similar to the adult distribution, suggesting that there are hydrodynamic mechanisms that function to retain the eggs in close proximity to the spawning grounds. Based on an examination of the variability in both surveys, the distribution of both the eggs and the adult fish is remarkably similarly from year to year

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(low coefficient of variation), suggesting that the population in the Gulf of Cadiz is both resident to the region and that the spatial distribution is stable over time. Along the Portuguese coast (subarea IXa north and central north), acoustic survey data indicates that the abundance of anchovy is considerably lower with much greater interannual variability than observed in the Bay of Cadiz. There appears to be a number of localized populations that are centred in estuaries along the coast of Portugal. There are occasional eruptions of anchovy along the coast, which may be due to an influx of adults from adjacent regions (Bay of Cadiz or Bay of Biscay), or an increase in local abundance during periods when environmental conditions are favourable. At present there is not enough information to support one hypothesis over the other. The ichthyoplankton survey suggests that egg production along the coast of Portugal is much lower than is observed in the Bay of Cadiz, and there is high interannual variability in the magnitude of egg production. Therefore, annual monitoring is recommended along the Portuguese coast to detect these eruptions, and allow for opportunistic harvests during periods when local abundance increases. The biomass trends in the north based on the acoustic survey appear to be more consistent with anchovy in the Bay of Biscay (Subarea VIII, ICES 2014, Figure 1). Spatial patterns in biomass may result from connectivity (vagrancy from larval retention areas in the Bay of Biscay or the Gulf of Cadiz) or similar environmental factors.

Figure 1. Trends in spawning stock biomass of anchovy in Bay of Biscay (top panel; ICES 2014) and trends in estimates of biomass from acoustic surveys (bottom panel; Ramos 2015). 58 | ICES SIMWG REPORT 2015

Oceanographic life cycle retention Anchovy population structure is influenced by larval retention mechanisms, which relate to dominant circulation features (Koutsikopoulos and Le Cann 2006). Fundamental differences in circulation patterns exist between the Western Iberian Coast and Sea of Cadiz, which are supportive of regional differences in genetics, discrete concentrations of eggs and adult biomass, and catch dynamics (Ramos 2015). Dominant geostrophic flow in shallow shelf regions of the Gulf of Cadiz is eastward (shoreward) (Criado-Aldeaneuva et al. 2006), which would favour retention of eggs and larvae within the Gulf. Along the Western Iberian Coast, transport and retention regimes are highly variable due to the combined influences river discharge, winds and upwelling on the Western Iberian Buoy- ant Plume and the Iberian Poleward Current (Santos et al. 2006). Strong upwelling events are expected to cause offshore displacements of eggs and larvae, but certain combinations of wind and advection strength can favour convergence zones and particle retention over Iberian shelf waters. More variable dispersal outcomes associated with the dynamic oceanic regime off the western Iberian Coast contrast with a presumably more stable one in the Gulf of Cadiz, which would be consistent with more stable egg and adult biomass distributions in the Gulf of Cadiz versus those observed along the Iberian Coast (Ramos 2015). Catch Trajectories Fishery landings data for Division IXa were available from 1989-2013, during which time landings ranged from 1,984 to 12,956 t. The majority of landings have come from the Spanish waters of the Gulf of Cadiz in the southern portion of Division IXa. However, in 1995 and 2011, the fishery was located in the northern portion of Division IXa with an increased proportion of the landings came from this region. It was speculated that the increase in anchovy abundance during these years was due to variation in oceanographic conditions that favoured reproduction and larval survival in this region (Ramos, 2015). Recent genetic studies did not include samples that were collected during 2011 (Zarraon- aindia et al., 2012; Vinas et al., 2014). Therefore, the origin of the fish caught during these large episodic events in the northern portion of Division IXa is unknown. Nonetheless, direct estimates of anchovy biomass along Division IXa corroborate the recent distribution of landings from the fishery. A correlation analysis of annual landings by Ramos et al. (2001) indicated that the landings from the southernmost areas of Division IXa differed from catch histories in other regions. These analyses also demonstrated there was not a strong correlation between catches from the southern and northern area one year later, suggesting that northward migrations are not likely responsible for fluctuations in catches. Life history information The life history data support phenotypic variation of anchovy within ICES Division IXa; however, these data were limited and alone would not support separating the Cadiz area from the more northern subdivisions of IXa. Size at age is smaller in the southern Cadiz region, but only two recent years can be compared so it is unknown if this distinction persists over time. The report comments, but does not present specifics, that there are also differences in size at maturity between these same subdivisions. If these life history traits are important for defining the stock structure, then it is recommended that these trends are monitored over several years. Also verification that these fish were aged in the ICES SIMWG REPORT 2015 | 59

same laboratory, or age agreement was cross-checked between laboratories, is recommended. Morphometric data The morphometric data support phenotypic differences within ICES Division IXa, including clinal variation along the Iberian peninsula. The primary source document Caneco et al. 2004 employed good practices such as using samples from more than one year to show temporal stability and morphometric measures using a truss system and corrections for fish size. Otolith shape There are two relevant publications with regard to stock identification of anchovy along the North Atlantic shelf edge and in the Mediterranean, using otolith shape analysis. The paper by Bacha et al. (2014) cited by Ramos (2015) includes a sample from the Gulf of Ca- diz, but none of the sub-divisions of area XIa further north. A clear separation of three groups of sampling sites was reported: the Gulf of Cadiz clustered with Northwest Mo- rocco, the Alboran Sea, and the Algerian coast. Oceanographic and geomorphologic boundaries were identified as environmental drivers for observed differences in otolith shapes of anchovy from these areas. Jemaa et al. (2015), not referenced in the Ramos (2015) review, use an expanded data set, encompassing sampling areas from the North Sea down to Northwest Africa, as well as further into the eastern Mediterranean. Within ICES Division XIa, however, only the southern part (Gulf of Cadiz) is covered by sampling. Therefore, these two studies do not contribute to the specific issue of stock structure of anchovy in ICES Division XIa.

Genetics The most exhaustive analysis of spatial genetic variation on European anchovy to date is offered by the study by Zarraonaindia et al. (2012), which analysed samples across the whole range of locations relevant to assessment and management issues considered by WGHANSA. While mitochondrial data fail to resolve fine scale population structure, the panel of 47 nuclear SNPs clearly separate the Northern (Bay of Biscay) from the Southern stock component (i.e. Bay of Cadiz). The focal issue, however, remains the status and identity of spawning groups found along the western Iberian coast, between Galicia (location 10) and Southern Portugal (location 12). In a principal component analysis plot of genotypes both Portuguese samples are situated in an intermediate position between northern and southern stock, exhibiting some degree of genetic distinctiveness (Figure 2). The Galician sample (in red) appears in turn subtly divergent from the Portuguese fish, making the stock boundaries around Iberia somewhat unclear (Figure 2). Neverthe- less, it is useful to point out that fish in locations 10, 11, 12 seldom account for a significant proportion of the catch along the shelf, and that the Galician sample was collected in 2010 from an estuarine area while other locations were sampled in 2008/2009, from more open coastal locations. Collective evidence points to the possibility that small local coastal/inshore populations may exhibit ‘boom and bust’ dynamics across the years, oc- casionally becoming a valuable local resource. However, given the lack of replication in sampling over time and spatial extent of sampling within years, and the unclear pattern of differentiation among these intermediate western Iberian samples, SIMWG finds no genetic support for the redefinition of assessment boundaries within this area. SIMWG 60 | ICES SIMWG REPORT 2015

notes that some flexibility will be required to adopt management measures that can assist sustainable exploitation of these local stocks.

Figure 2. Principal Component Analysis plot of all individual multilocus genotypes based on 47 nuclear SNPs from locations 9 to 13 from Zarraonaindia et al. (2012). Image kindly provided by I. Zar- raonaindia.

Conclusions and Recommendations The working document by Ramos (2015) provides a comprehensive review of the information available on substock structure of European anchovy in the Bay of Biscay and Iberic waters. There is evidence to support a resident population of anchovy located in the Bay of Cadiz (ICES Subdivision IXa South). However, there is little information regarding the origin of European anchovy in ICES Subdivision IXa North, North Central, South Central. Before changing the current stock unit for anchovy, there is a need for research to improve understanding of the source of fish off the coast of Portugal and Gali- cia, specifically whether these are local sustaining populations or represent spillover from adjacent populations in the Bay of Biscay or Gulf of Cadiz. SIMWG recommends that the current stock structure stand and recommends the continued approach of employing spatially explicit management and monitoring of this subdivision. If analytical assessments are going to be developed, stock identity should be determined and the question of whether there is a self-sustaining anchovy population on the Iberic shelf or occasional vagrancy from the more stable populations in the Gulf of Cadiz and Bay of Biscay should be addressed. ICES SIMWG REPORT 2015 | 61

References

Criado-Aldeanueva, F., J. Garcia-Lafuente, J. Miguel Vargas, J. Del Rio, A. Vázquez, A. Sánchez. 2006. Retention and circulation of water masses in the Gulf of Cadiz from in situ observations. Dea-Sea Research II: 1144-1160.

ICES. 2014. Report of the Working Group on Southern Horse Mackerel, Anchovy and Sardine (WGHANSA), 20-25 June 2014, Copenhagen, Denmark. ICES CM 2014/ACOM: 16. 599 pp.

Koutsikopoulos, C. and Le Cann, B. 2006. Physical processes and hydrological structures related to the Bay of Biscay anchovy. Scientia Marina 60 (Suppl 2): 9-19.

Ramos, F., Uriarte, A., Millán, M., Villamor, B., 2001.Trial analytical assessment for anchovy (En- graulis encrasicolus, L.) in ICES Subdivision IXa-South. Working Document presented to the ICES Working Group on the Assessment of Mackerel, Horse Mackerel, Sardine and Anchovy (WGMHSA). ICES, C.M. 2002/ACFM: 06.

Ramos, F. 2015. Working document presented in the: ICES Stock Identification Methods Working Group (SIMWG). 10-12 June 2015. Oon the population structure of the European anchovy (En- graulis encrasicolus) in ICES Division IXa: a short review of the state of art. 22 p.

Santos, A.M.P., Peliz, A., Dubert, J., Oliveira, P.B., Angélico, M.M., Ré, P. 2004. Impact of a winter upwelling envent on the distribution and transport of sardine (Sardina pilchardus) eggs and larvae off western Iberia: a retention mechanism. Continental Shelf Research, 24: 149-165.

Viñas, J., Sanz, N., Peñarrubia, L., Araguas, R.M., García-Marín, J.L., Roldán, M.I., Pla, C. 2014. Ge- netic population structure of European anchovy in the Mediterranean Sea and the Northeast Atlantic Ocean using sequence analysis of the mitochondrial DNA control region. ICES Journal of Marine Science, 71: 391–397.

Zarraonaindia, I., Iriondo, M., Albaina, A., Pardo, M.A., Manzano, C., Grant, W.S., Irigoien, X., and Estonba, A. 2012. Multiple SNP Markers Reveal Fine-Scale Population and Deep Phylogeo- graphic Structure in European Anchovy (Engraulis encrasicolus L.). PLoS ONE 7(7): e42201. doi:10.1371/journal.pone.0042201.

Doug Zemeckis [email protected] 62 | ICES SIMWG REPORT 2015

Annex 9: Evaluation of Megrim Stock Identity in ICES Subareas VIIIc and IXa

ECOREGIONS: Bay of Biscay and Iberic waters

ICES STOCK(S): 1. North: Megrim (Lepidorhombus whiffiagonis) in Divisions VIIb-k and VIIIabd 2. South: Megrim in Divisions VIIIc and IXa

SIMWG FINDINGS: SIMWG does not find biological support for combining the northern (ICES Divisions VIIb-k and VIIIabd) and southern (ICES Divisions VIIIc and IXa) stocks of megrim together and contends that the current stock separation stands. A key paper on population structure of megrim showed a peculiar degree and pattern of genetic separation which merits further review.

Background

SIMWG was requested by Working Group for the Bay of Biscay and the Iberic Waters Ecoregion (WGBIE) in 2014 to provide feedback on issues of stock identity of megrim (Lepidorhombus whiffiagonis) in VIIIc and IXa. WGBIE considers that the stock of megrim in VIIIc and IXa is likely a southern extension of the northern stock of megrim in VII and VIIIabd) and that a joint assessment of those two stocks could be envisaged. WGBIE requested that SIMWG review the limits of the two stocks.

In the 2015 WD, Abad (2015) proposed a revision to the management units of European anchovy from the current single unit stock in ICES Division IXa to a proposed two stock unit:

Current ICES stock units: 1. North: Megrim in Divisions VIIb-k and VIIIabd 2. South: Megrim in Divisions VIIIc and IXa

Proposed revision to ICES stock units: 1. A combined North and South Megrim stock unit (including Divisions VIIb-k and VIIIabd, VIIIc and IXa) Genetics The Working Document provided by WGBIE refers to a paper by Danancher & Garcia- Vasquez (2009) as the most recent and relevant source for population genetic structure information on megrim (both Lepidorhombus whiffiagonis and L. boscii). SIMWG’s examination of Danancher & Garcia-Vasquez (2009) revealed somewhat puzzling results, particularly concerning were reported levels of genetic structure (global FST~0.2) that were one to two orders of magnitude greater than any other marine fish examined with similar techniques over comparable distributions. Additionally, pairwise comparisons were all highly significant (with the exception of the two Celtic Sea divisions, Figure 1), indicating large differentiation among every sample. Furthermore, beside the level of genetic differentiation, the patterns of divergence were confusing. The multidimensional scaling plot ICES SIMWG REPORT 2015 | 63

depicts the relationships among all the screened samples, and it shows how, surprisingly, the most northern population in the West of Scotland bears greatest similarity with the most remote population inside the Mediterranean basin (Figure 1). The two divisions VIII (Cantabria and Biscay) appear extremely divergent, while the Portuguese/Galician shelf in area IX is more similar to the Cantabrian, but still separated by a significant FST=0.05 (which in any other marine context would be deemed considerable - it is 2-5 times greater than the overall FST detected in cod across the whole North Sea, Irish Sea and English Channel; Hutchinson et al. 2001).

Figure 1. Multidimensional scaling plot among megrim samples, based on nuclear microsatellites.

The individual-based Bayesian clustering also showed some results that are difficult to interpret, including several individuals caught in VI that are strongly assigned to the Mediterranean, and strong grouping of the most southern Iberian samples with the Celtic Sea. SIMWG contends that the Danancher & Garcia-Vasquez data should be reanalysed to resolve the questions raised above. At this time SIMWG suggests WGBIE not rely on these genetic results as a basis for assessment of spatial stock structure of megrim in the areas of interest until further study of results is made. Growth Information Landa et al. (2000) used otoliths to back calculate growth of L. whiffiagonis collected in areas VIIchjk, VIIIab, VIIIc, and IXa (n = 746). Their analysis revealed megrim exhibit sex- ually dimorphic growth, with females growing faster and attaining a larger maximum size than males. Landa et al. (2000) also found evidence for a latitudinal gradient in growth, with megrim in area IXa exhibiting the smallest maximum size and fastest growth rates. Alternatively, megrim in subarea VII reached the largest maximum size, and the lowest growth rates. Growth in subarea IXa appeared to be asymptotic, while the length of megrim in subarea VII appeared to increase linearly with age. Despite the apparent geographic differences in growth that were detected during this study, the results are somewhat equivocal, because the age range of fish sampled in area IXa (ages 1- 64 | ICES SIMWG REPORT 2015

3) was much smaller than the age range of megrim sampled in the other zones. Landa et al. (2000) also provided a summary table (Table 1) describing the von-Bertalanffy growth parameters for megrim in each subarea based on prior published studies. The available information on growth rates for this species do not support combining the north (VIIb-k and VIIIabd) and south stock areas (VIIIc and IXa) for megrim, as difference in growth suggest that megrim in these subregions would likely respond differently to exploitation and environmental change. Future directed studies to investigate the growth rates of megrim in subareas IXa and VIIIC could benefit by sampling individuals across a wider range of age classes, which would allow for more direct comparison of growth rates across geographic subregions.

Table 1. Von-Bertalanffy growth parameters for megrim across subareas. Table 6 from Landa et al., (2000).

Commercial CPUE Data Sanchez et al. (1998) provided spatially specific CPUE data from the Spanish trawl fleet for L. whiffiagonis in subareas VII, VIII and IX. The CPUE plots demonstrate discrete (non-continuous) distribution patterns in the catch of megrim along the coast (Figure 2). However, because megrim is primarily a bycatch species, it is unclear whether the geographic patterns in CPUE accurately reflect the distribution of megrim, or whether these patterns are indicative of the major fishing grounds that are targeted by the mixed species trawl fishery. An analysis of fishery-independent data would help to elucidate this question further. However, the figure clearly indicates that CPUE of megrim is substantially higher in Subarea VII than in subarea IXa, suggesting that the productivity and abundance of megrim varies across subareas. Therefore, combining all of these subareas into a single stock may violate the unit stock assumption, and may lead to the overexploitation of the less productive populations of megrim in subarea IXa. ICES SIMWG REPORT 2015 | 65

Figure 2 CPUE (kg hour-1) of the Spanish fleet in the megrim ICES area (Figure 15 from Sanchez et al. 1998).

Asynchrony among Megrim Advisory Units WGBIE considered that the southern advisory unit of megrim (VIIIc and IXa; Bay of Bis- cay and Atlantic Iberian waters) may be a fringe of the much larger northern stock (VIIb– k and VIIIa,b,d; CelticSea and West of Scotland) and that combining the advisory units may be warranted. The hypothesis of a single stock was tested by comparing trends in estimates of recruitment, spawning stock (SSB) and fishing mortality (F) between the northern (VIIb–k and VIIIa,b,d) and southern (VIIIc and IXa) advisory units from the most recent ICES advice (ICES 2014). Common trends were tested using Pearson correlation coefficients and annual estimates were standardized for graphic comparison. General trends in stock size were similar (r=0.58), with both stocks generally decreasing for most of the assessment series and increasing during the last decade (Figure 3). How- ever, there were also some considerable differences in stock trends (e.g., the northern stock generally increased during the 1990s, but the southern stock generally decreased during the 1990s). The general trends in stock size resulted from different trends in recruitment (r = -0.21) and fishing mortality (r = -0.20). 66 | ICES SIMWG REPORT 2015

Figure 3. Trends in recruitment, stock size and fishing mortality for northern and southern megrim stocks.

Conclusions and Recommendations Upon review of the available data on megrim, SIMWG does not find strong evidence to support combining the northern (ICES Divisions VIIb-k and VIIIabd) and southern (ICES Divisions VIIIc and IXa) stock areas. Differences in growth rate, patterns in the distribution of CPUE, and asynchrony in recruitment trends do not support combining the current northern and southern megrim stocks into a single stock unit. Furthermore, a key paper on genetic structure of megrim showed a peculiar degree and pattern of genetic ICES SIMWG REPORT 2015 | 67

separation which merits further review before it could be used as basis for changing existing stock units. SIMWG recommends that the current stock separation stand. References

Abad, E. 2015. Reconsidering the Lepidorhombus whiffagonis in VIIc & IXa stock boundaries. Work- ing document for the ICES Stock Identification Methods Working Group. 8 pp.

Danancher, D. & E. García-Vázquez, 2009. Population differentiation in megrim (Lepidorhombus whiffagonis) and four spotted megrim (Lepidorhombus boscii) across Atlantic and Mediterranean waters and implications for wild stock management. Marine Biology, 156:1869–1880.

Hutchinson WF, Carvalho GR, Rogers SI, 2001. Marked genetic structuring in localised spawning populations of cod Gadus morhua in the North Sea and adjoining waters, as revealed by microsatellites. Marine Ecology Progress Series, 223:251-260.

ICES. 2014. Report of the ICES Advisory Committee 2014. ICES Advice, 2014. Books 1-11.

Landa, J. and C. Piñeiro, 2000. Megrim (Lepidorhombus whiffiagonis) growth in the North-eastern Atlantic based on back-calculation of otolith rings. ICES Journal of Marine Science, 57: 1077– 1090.

Sánchez, F., Pérez, N. and J. Landa, 1998. Distribution and abundance of megrim (Lepidorhombus boscii and Lepidorhombus whiffiagonis) on the northern Spanish shelf. ICES Journal of Marine Sci- ence, 55: 494-514.

Doug Zemeckis [email protected]