Gadoid fisheries: the ecology and management of rebuilding

This Symposium issue results from the ICES/NAFO symposium on “Gadoid Fisheries: The Ecology and Management of Rebuilding”, held in St Andrews, New Brunswick, Canada, from 14 to 18 October 2013. The aim of the Symposium was to (i) address the historical dynamics and current status of gadoid stocks worldwide, (ii) present new scientific findings on the biology and ecology of these species that can be used to improve fisheries management, (iii) link biological changes to environmental changes that can be used to forecast species distribution and productivity related to climate change, and (iv) present and appraise the effectiveness of management actions before, during, and after recovery. The Symposium targeted gadoids, namely cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollock (Pollachius spp.), hake (Merlucciius spp.), and others. Gadoids remain one of the key groups of exploited demersal fish. The histories of many gadoid fisheries have featured rapid population decline and fishery collapse. Recently, marked improvements in population sizes have occurred in many gadoid stocks spanning their geographic distributions. Many other stocks, however, remain at depleted levels. Given the commercial value and ecological importance of this group of fish, the Symposium was strongly justified. Over 100 participants representing Australia, Brazil, Canada, Chile, Denmark, Finland, France, Germany, Japan, Norway, Russia, Spain, the United Kingdom, and the United States presented empirical data and theories to offer insight into the varied recovery rates of gadoid stocks in 56 oral contributions and 39 posters. Agenda and abstracts from the symposium are available in the Supplementary Data There has not been an international symposium dedicated to the biology and ecology of Atlantic cod since the early 1990s (those were held in St John's, Canada, and Reykjavik, Iceland). In 2006, a Wakefield-sponsored symposium on the resiliency of gadoid stocks to fishing and climate change was held in Anchorage, Alaska, with the programme heavily focused on North Pacific gadoids. In 2009, an ICES/PICES/UNCOVER symposium on rebuilding depleted fish stocks—biology, ecology, social science, and management strategies—was held in Rostock, Germany, addressing mechanisms of fish stock recovery and how to best implement stock recovery plans. The ICES/NAFO Symposium in St Andrews went beyond these earlier symposia by contrasting gadoid stock dynamics in different ecosystems on both sides of the Atlantic, identifying not only ecological settings and management actions leading to recovery, but also considering management plans after, and in the absence of, rebuilding. The symposium acknowledged explicitly the challenges of environmental change and species interactions, and that gadoid species differ significantly in key biological attributes that influence stock management advice through implementation of suitable management reference points, harvest levels, closed areas and seasons, and fishing gear. The symposium was structured into six theme sessions: effects of life history on productivity and stock rebuilding; the ghost of fishing past: effects of fishing on recovery potential; climate change and stock rebuilding; case histories of successful or failed rebuilding; community ecology and stock rebuilding: effects of predators, prey, and competitors; stock assessment and fisheries management. The opening keynote address on “The collapse of Canadian groundfish stocks—an eye witness account” was delivered by Jean-Jacque Maguire (Canada). Additional keynote speakers included Peter Wright (UK) in session 1 “Are there useful life history indicators of stock recovery rate?”, Jeffrey Hutchings (Canada) in session 2 “Ghosts of fisheries-induced depletions: do they haunt us still?”, Svein Sundby (Norway) in session 3 “Fish populations in a changing climate—thermal effects, effects of other abiotic factors and effects through the ecosystem!”, Peter Shelton (Canada) in session 4 “Successes and failures in rebuilding North Atlantic cod stocks”, Anna Rindorf (Denmark) in session 5 “Fast growing fish living dangerous lives: Gadoids in the North Atlantic”, and Terrance Quinn (USA) in session 6 “Stock assessment and fisheries management of gadoids in the North Pacific”. The wide variability in life history traits observed among gadoid species/stocks and how these are associated with recruitment and rebuilding was a central theme of the symposium. Examination of the relation between early survival and age at maturity in many gadoid stocks (Wright, 2014) revealed that early maturing stocks have the potential for high population growth following favourable recruitment events, but generally low early survival rates imply that a faster recovery of early vs. late maturing stocks cannot, as a rule, be expected. It appears difficult to infer recovery potential from life history characteristics as regional variations in reproductive success ultimately shape local reproductive schedules. Life history characteristics within a stock are not independent of each other; Lambert and Ouellet (oral presentation; abstract available in the Supplementary Data) identified covariation patterns in growth, reproductive characteristics, and mortality for the northern Gulf of St Lawrence cod stock. Age-specific survival and reproductive rates derived from these patterns indicate important changes in stock productivity related to temperature regimes with a concurrent reduction in the resilience of stocks to exploitation at colder temperatures. Linkages of reproductive traits and nutritional condition were reported for other gadoid stocks, including skipped spawning in Northeast Arctic cod (Skjæraasen et al., oral presentation), larval condition and survival (Bachan et al., poster presentation), and reproductive success for Chilean hoki (Macruronus magellanicus; Payá, oral presentation). Poor nutritional conditions in periods of stock collapse were also reported for other stocks, e.g. the northern cod (Morgan et al., 2014). Several of the symposium presentations touched on the importance of considering substock structure and population complexity. There is concern about the loss of subpopulations that may be locally adapted (Wright, 2014) and that we may not be managing at the right spatial scales/stock unit. Linking spatial dynamics and stock structure of gadoids with stock development, uncertainty in stock assessments and management success was a central theme with a series of contributions, including results from a multidisciplinary review study (Zemeckis et al., 2014a,b) and application of modern tagging technology, biochemistry, and molecular genetics to identify stocks (e.g. Johanessen et al., oral presentation; Subbey et al., oral presentation). Results indicate that present stock assessments (i) mask underlying subpopulation trends, potentially contributing to poor status of stocks with high population diversity (Holmes et al., 2014), (ii) disguise stock declines when sharing habitat with stocks in healthy condition (Michalsen et al., 2014), and (iii) conceal negative stock development in areas neighbouring recovering stocks showing a geographical expansion with increasing density (Eero et al., 2014). Fine-scale studies on spawning behaviour deploying acoustic telemetry revealed (i) diel and gender-based spawning behaviour (Dean et al., 2014) and (ii) identified spawning site fidelity as mechanism contributing to the formation and maintenance of metapopulation structure, reducing the reproductive connectivity among spawning sites, thus delaying both the recolonization of abandoned spawning sites and stock rebuilding (Zemeckis et al., 2014a,b). Fishing on spawning grounds impacts the formation of spawning aggregations, i.e. the impact goes beyond the removal of individuals from the spawning stock (Dean et al., 2014). Larger-scale tagging experiments confirmed gender-specific spawning behaviour (Behrens et al., poster presentation), but also showed different movement patterns among spawning groups. Size-based movements differed among spawning groups, with open coast and offshore bank groups exhibiting more homogenous movement patterns than those inhabiting bays (Loehrke and Cadrin, oral presentation). Spawning patterns were surprisingly stable, unless regional physical conditions constrained the suitability of the spawning grounds resulting in the displacement of spawning aggregations (Höffle et al., 2014). Future stock assessment models and fishery management plans should consider the existence of complex stock structure or metapopulations. To accomplish this, enhanced resolution and knowledge of population structures, life history traits, and their spatial dynamics are required and several contributions presented technologies and methodologies to acquire this information (e.g. Conroy et al., poster presentation; Godisksen et al., poster presentation; Otterå and Skilbrei, poster presentation). Surveying depleted stocks has proven difficult and alternatives to standard trawl surveys were addressed by a number of contributions, i.e. for groundfish stocks in the eastern Gulf of Maine (Runnebaum et al., poster presentation), for Chilean hake (Merluccius gayi; Acuña et al., poster presentation) and European hake (Merluccius merluccius; Garcia, oral presentation), including an application of the egg production method (Guevara-Fletcher et al., oral presentation). Other contributions focused on the predictability of spawning ground utilization considering life history, fisheries-induced changes in demography and environmental conditions (Opdal et al., oral presentation; Höffle et al., poster presentation), or the effect of long-term area closures (Sherwood and Grabowski, poster presentation). Attention to within stock diversity is a critical objective for rebuilding stocks and fisheries. The importance of interactions with other taxa in determining the productivity of gadoid stocks, and how this may limit or enhance stock rebuilding was addressed in a series of contributions. These included studies on the effects of predation by marine mammals on gadoid recovery as well as bottom-up processes that link physical dynamics, primary production, and prey abundance to body growth, recruitment, survival, and recovery of gadoid stocks (e.g. Hammill et al., 2014; Neumann et al., 2014). Rindorf (oral presentation) summarized the key processes at work as (i) low abundance of prey fish impairs growth and increases cannibalism, (ii) at low abundance, gadoids may end up in predatory pits from which they can only escape if there is a large year-class, and (iii) not knowing natural mortality makes predicting recovery highly uncertain. This demonstrates the need for observing and predicting changes in predator–prey relationships. The question of top-down control of gadoid stock dynamics by seals was taken up. A study on grey seal (Halichoerus grypus) diet composition on cod overwintering grounds in the southern Gulf of St Lawrence revealed the highest ever reported contributions of cod to grey seal diet (Hammill et al., 2014). Seal feeding aggregations co-occur in time and space with large demersal fish aggregations and comparison of diet compositions and prey abundance indicates that seals prefer large cod and white hake (Urophycis tenuis; Benoit et al., oral presentation), actively targeting water layers of high cod abundance (Harvey et al., poster presentation). In combination with dramatic increases in seal abundance, these findings suggest that a seal predation-related elevation in natural mortality is preventing stock recovery of cod and white hake (Swain et al., poster presentation) through a predator pit or predation-driven Allee effect (Swain and Benoît, oral presentation). Apart from seals and marine mammals, the impact of other top predators on gadoid stocks, such as spiny dogfish (Squalus acanthias) in the Gulf of Maine (Kersula et al., poster presentation) and Humboldt squid (Dosidicus gigas), preying on Chilean hake (Neira and Arancibia, poster presentation) was investigated. There was a debate about the impact of the giant Humboldt squid on Chilean hake, with Payá et al. (oral presentation) presenting evidence of a substantial impact on hake recruitment and fishing mortality, alongside with environmental factors, while Neira and Arancibia (poster presentation) concluded that predation by squid was not the primary factor behind the collapse of the hake stock. Independent of the cause, simulations indicate that high natural mortality rates will prevent Chilean hake recovery, independent of the fisheries management enforced (Pedrazza-Garcia and Cubillos, poster presentation). Predation on early life stages by pelagic fish has been reported for different gadoid stocks, but direct evidence of an impact on recovery is lacking, probably because a variety of processes affect recruitment, e.g. prey availability (Hornaff et al., poster presentation) interlinked with ambient temperature (Fouzai et al., oral presentation). The eastern Baltic cod stock is no exception, but evidence was presented that a release from egg predation by clupeids has contributed to the recovery of the stock (Neumann et al., 2014). Predation on post-settlement juvenile cod in the Gulf of Maine by longhorn sculpin (Myoxocephalus octodecemspinosus) and sea raven (Hemitripterus americanus) was reported by Auster et al. (poster presentation), with increasing abundances of these predators and concurrent increasing spatial overlap with juvenile cod throughout the last decade. Density-dependent mechanisms were identified as regulating the spatial distribution of juvenile Chilean hake, including cannibalism arising from spatial overlap with adult hake (Pérez-Cuesta and Cubillos, poster presentation). Climate-induced changes in distribution alter spatial overlap between predator, prey, and competitors, as demonstrated for North Sea saithe (Pollachius virens) and European hake (Cormon et al., 2014). The importance of suitable feeding and refuge areas, and negative effects of a reduction in their availability on recruitment, was demonstrated for Norwegian coastal cod (Michaelsen et al., poster presentation; Pedersen et al., poster presentation). Variation in forage fish supply impacts growth, condition, and maturation of gadoids, as exemplified by case studies on Gulf of Maine cod (Arnes, poster presentation), North Sea whiting (Merlangius merlangus; Lauerburg et al., oral presentation), and northern cod (Carruthers and Rose, oral presentation). In addition, density-dependent growth was identified for Northeast Arctic and North Sea saithe (Devine et al., poster presentation), leading to the suggestion that growth and potentially sexual maturity should be dynamically integrated in multispecies models, e.g. as a function of prey abundance. In this respect, sexual dimorphism in food intake and resultant growth (Keyl et al., oral presentation; Lauerburg et al., poster presentation) and natural mortality (Clark, poster presentation) must be considered. A comparison of haddock diet in different parts of the North Atlantic (Link et al., poster presentation) revealed shifts in dietary focus from being piscivor to benthivor over time in any given ecosystem. This has implications for haddock population dynamics, the resident fish community, and the entire ecosystem and confirms the need for observing and predicting changes in predator–prey relationships. Effects of declining gadoid stocks on ecosystem structure were studied for a variety of ecosystems: (i) the Chilean northern–central coastal system with Chilean hake playing an important role as predator of red and yellow squat lobsters (Pleuroncodes monodon; Arancibia et al., oral presentation), (ii) the southern Chilean system with adult southern hake (Merluccius australis) and hoki as well as kingklip (Genypterus chilensis) being major predators on juvenile hoki, southern blue whiting (Micromesistius australis), and juvenile southern hake (Neira and Arancibia, oral presentation; Giacaman-Smith and Neira, poster presentation), and (iii) a Norwegian fjord, showing increasing prey populations such as shrimp (Pandalus borealis), capelin (Mallotus villosus), and herring (Clupea harengus; Pedersen et al., poster presentation). In all these cases, the decline of gadoid stocks was accompanied by changes at other trophic levels. Meta-analyses and simulations and 2014) suggest that (i) Allee effects can be in depleted (ii) the the of population the the uncertainty of recovery, (iii) populations are more to environmental than which may and the uncertainty of recovery, and (iv) the of fisheries-induced for recovery need not be effects of fishing were reported for a number of stocks, i.e. on growth rates (Pedrazza-Garcia et al., poster presentation) and maturation (Wright, poster presentation), these processes with other environmental an of and life history for Northeast Arctic and (oral presentation) that a population adapted only to natural mortality has a of population change and low resilience to fishing individuals to the by earlier in life and by more and both of these changes to a more rapid of population change and faster to environmental In a current high natural mortality in the southern Gulf of St Lawrence cod is fishing mortality as the of early maturity oral presentation). the temperature and many and life history and of climate change are for and the of marine temperature change is also accompanied by other key physical factors that influence stock productivity and influence trophic of the ecosystem as that there are many potential for climate change impact on fish stocks oral presentation). The northern North Atlantic is a ecosystem in which the of the is to the A question is and species can with dynamics as the to and species are A predicting for life histories and behaviour of cod was to identify of survival, growth, and and oral presentation). changes the maturation reproductive and beyond is by and there are interactions with fishing change life history of cod in and stocks may differ in their and oral presentation). Results suggest that on the ecological and are not over in many cod stocks can be by of management by favourable environmental conditions Arctic et al., oral presentation; and poster presentation; Baltic et al., oral presentation). The role of recruitment variability on population resilience to fishing and to from through studies et al., 2014), revealed that (i) the the recruitment the and the time required for the population to decline of (ii) the time required to to of after fishing not differ between of environmental recruitment variability to uncertainty in recovery and (iii) these patterns are The importance of reproductive success for stock recovery was also for other stocks, such as Chilean hoki and Cubillos, poster presentation). These findings suggest that increases in recruitment variability resilience to fishing and uncertainty in recovery, fisheries management. for gadoids are to in high areas of the Northeast Atlantic et al., oral presentation; et al., poster presentation), while of suitable habitat may prevent a development in the Atlantic and oral presentation). The was demonstrated by application of a to of species considering species life histories and habitat poster presentation). In more gadoid species may their distribution into northern Atlantic and oral presentation), while for are more because of complex processes and oral presentation) and uncertainty how will affect stock and ecosystem dynamics and oral presentation). In an to the effects of climate change, and predation for the southern Gulf of St Lawrence et al. (poster presentation) concluded that density-dependent processes and effects of predation to be the for observed distribution Maguire (oral presentation) an of the leading to the collapse of the Canadian groundfish stocks in the late and early The of environmental and changes in natural mortality, and is to be after the to that a different of have the collapse. A management system not only science, but also and must be to that and are management must a between and social i.e. recruitment, high natural mortality, low growth as well as high fishing have recovery of Atlantic cod stocks, with both changes in ecosystem settings and in stock assessments being as exemplified for the northern cod et al., oral presentation) and cod in the southern Gulf of St Lawrence (Swain et al., poster presentation). geographical not imply that stocks as demonstrated by the contrasting stock dynamics of stocks in et al., oral presentation) and cod in the Baltic (Eero et al., 2014). on findings of the ICES/PICES/UNCOVER symposium on rebuilding depleted fish stocks ecology, social science, and management and with fisheries management, Shelton (oral presentation) summarized factors required for stock rebuilding: (i) management (ii) a rapid reduction in fishing mortality through a management that a harvest control rule, (iii) data and stock (iv) among participants (e.g. and on assessment low implementation absence of recruitment and in reproductive success and juvenile The of the information from stock assessment for fishery management gadoid assessments are on highly complex models that well for determining in the of e.g. oral presentation). Other assessments have with data and uncertainty (e.g. Pacific and do not have information for advice on have been to for new e.g. increasing natural mortality, stock and population as well as climate shifts on recruitment, as in the is being used to the of assessment models, i.e. (i) impact of movements and of cod New et al., 2014), (ii) of between biological population structure and management et al., 2014), and (iii) application of management e.g. for Chilean hoki et al., oral presentation) and et al., oral presentation). There is an in with uncertainty and in data and of stock how to uncertainty in data and to and changing natural oral presentation; oral presentation). In this respect, an may be to harvest control oral presentation). Apart from stock the to reference for management changing productivity (Morgan et al., 2014) and changing compositions et al., poster presentation) were and the to address management after rebuilding oral presentation) were both fish stocks and international and more in assessment and management. This is in the development of and management management is about managing and there is increasing of the need to not only ecological but also and social and of management (e.g. oral presentation; Arancibia et al., poster presentation). rebuilding an to improve assessment and management. can development of management The the need for among participants science, and and The held at the was by and and the of The of the and (Canada) and The for the of this symposium as of in the of the while present at the symposium and those present to for The as was given by Lambert and (Canada). to and of the St Andrews as well as of and of the and the that this symposium a and of the symposium was by St Andrews and of Denmark, of the Canadian and the for which the are

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.