Guidelines for incorporating fish distribution shifts into a fisheries management context

The impacts of climate change have been demonstrated to influence fisheries resources. One way climate has affected fish stocks is via persistent shifts in spatio‐temporal distribution. Although examples of climate‐forced distribution shifts abound, it is unclear how these shifts are practically accounted for in the management of fish stocks. In particular, how can we take into account shifting stock distribution in the context of stock assessments and their management outputs? Here, we discuss examples of the types of fish stock distribution shifts that can occur. We then propose a decision tree framework of how shifting stock distributions can be addressed. Generally, the approaches for addressing such shifts fall into one of three main alternatives: re‐evaluate stock identification, re‐evaluate a stock unit area, or implement spatially explicit modelling. We conclude by asserting that the approach recommended here is feasible with existing information and as such fisheries managers should be able to begin addressing the role of changes in stock distribution in these fish stocks. The implications of not doing so could be notably undesirable.     

Transform high seas management to build climate resilience in marine seafood supply

Climate change is projected to redistribute fisheries resources, resulting in tropical regions suffering decreases in seafood production. While sustainably managing marine ecosystems contributes to building climate resilience, these solutions require transformation of ocean governance. Recent studies and international initiatives suggest that conserving high seas biodiversity and fish stocks will have ecological and economic benefits; however, implications for seafood security under climate change have not been examined. Here, we apply global‐scale mechanistic species distribution models to 30 major straddling fish stocks to show that transforming high seas fisheries governance could increase resilience to climate change impacts. By closing the high seas to fishing or cooperatively managing its fisheries, we project that catches in exclusive economic zones (EEZs) would likely increase by around 10% by 2050 relative to 2000 under climate change (representative concentration pathway 4.5 and 8.5), compensating for the expected losses (around ?6%) from ‘business‐as‐usual’. Specifically, high seas closure increases the resilience of fish stocks, as indicated by a mean species abundance index, by 30% in EEZs. We suggest that improving high seas fisheries governance would increase the resilience of coastal countries to climate change.     

Interannual-decadal variability of demersal fish assemblages in the Tsushima Warm Current region of the Japan Sea: Impacts of climate regime shifts and trawl fisheries with implications for ecosystem-based management

Data sets for two bottom trawl fisheries, the coastal pair-trawler fishery and offshore single-trawler fishery in the Tsushima Warm Current (TWC) region of the Japan Sea, were compiled and analyzed for the last three decades (1974-2006). These data sets were used to (1) identify and compare the variability in demersal fish assemblages, and (2) relate these to water temperature to examine the impacts of climate regime shifts. Principal component analysis (PCA) of catches of target species in the two trawler fisheries showed synchronous decadal variability with step changes around 1986/1987 and 1996/1997. These step changes strongly suggest the effect of the late 1980s climate regime shift, which was characterized by an abrupt change from a cool to a warm condition in the TWC. The first and second principal components (PC1 and PC2) for both trawler fisheries agreed closely with winter and summer water temperature in the Japan Sea, respectively, suggesting PC1 (PC2) was associated with cold- (warm-) water species. However, between warm- and cold-water species the response pattern to water temperature was different. CPUE (catch per unit effort) of warm- (cold-) water species correlated positively (negatively) with water temperature, indicating the increase in water temperature has a positive (negative) effect on warm- (cold-) water species. Cold-water species decreased (increased) both in biomass and distribution during the warm (cold) regime, while warm-water species increased in biomass and/or distribution during the warm 1990s. These results suggested that the demersal fish assemblage structure changed abruptly as a consequence of the late 1980s climate regime shift. Impact of fishing was unclear on the demersal fish assemblage as a whole, but fishing pressure has been intensified for specific species under unfavorable climate regimes even with a declining fishing effort. Differing response patterns between warm- and cold-water species to climate regime shifts suggest the importance of integrated assessment and ecosystem-based management for the whole trawl fishery rather than only for individual target species.     

Quantifying uncertainty in the wild‐caught fisheries goal of the Ocean Health Index

Sustainability indices are proliferating, both to help synthesize scientific understanding and inform policy. However, it remains poorly understood how such indices are affected by underlying assumptions of the data and modelling approaches used to compute indicator values. Here, we focus on one such indicator, the fisheries goal within the Ocean Health Index (OHI), which evaluates the sustainable provision of food from wild fisheries. We quantify uncertainty in the fisheries goal status arising from the (a) approach for estimating missing data (i.e., fish stocks with no status) and (b) reliance on a data‐limited method (catch‐MSY) to estimate stock status (i.e., B/B_MSY). We also compare several other models to estimate B/B_MSY, including an ensemble approach, to determine whether alternative models might reduce uncertainty and bias. We find that the current OHI fisheries goal model results in overly optimistic fisheries goal statuses. Uncertainty and bias can be reduced by (a) using a mean (vs. median) gap‐filling approach to estimate missing stock scores and (b) estimating fisheries status using the central tendency from a simulated distribution of status scores generated by a bootstrap approach that incorporates error in B/B_MSY. This multitiered approach to measure and describe uncertainty improves the transparency and interpretation of the indicator and allows us to better understand uncertainty around our OHI fisheries model and outputs for country‐level interpretation and use.     

Rebuilding Mediterranean fisheries: a new paradigm for ecological sustainability

In Mediterranean European countries, 85% of the assessed stocks are currently overfished compared to a maximum sustainable yield reference value (MSY) while populations of many commercial species are characterized by truncated size‐ and age‐structures. Rebuilding the size‐ and age‐structure of exploited populations is a management objective that combines single species targets such as MSY with specific goals of the ecosystem approach to fisheries management (EAF), preserving community size‐structure and the ecological role of different species. Here, we show that under the current fishing regime, stock productivity and fleet profitability are generally impaired by a combination of high fishing mortality and inadequate selectivity patterns. For most of the stocks analysed, a simple reduction in the current fishing mortality (F_cur) towards an MSY reference value (F_MSY), without any change in the fishing selectivity, will allow neither stock biomass nor fisheries yield and revenue to be maximized. On the contrary, management targets can be achieved only through a radical change in fisheries selectivity. Shifting the size of first capture towards the size at which fish cohorts achieve their maximum biomass, the so‐called optimal length, would produce on average between two and three times higher economic yields and much higher biomass at sea for the exploited stocks. Moreover, it would contribute to restore marine ecosystem structure and resilience to enhance ecosystem services such as reservoirs of biodiversity and functioning food webs.     

Review of climate change impacts on marine fisheries in the UK and Ireland

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Evaluating the effects of climate change in the southern Benguela upwelling system using the Atlantis modelling framework

The ocean is affected by multiple anthropogenic stressors including climate change, the effects of which are already evident in many ocean ecosystems. The ABACuS v2 end‐to‐end model together with climate projections from the NEMO‐MEDUSA 2.0 model were used to evaluate the effects of fishing, warming and horizontal and vertical mixing on the southern Benguela upwelling system. Of the drivers examined in this study, warming had the greatest effect on species biomass, with mainly negative effects. The magnitude of the impacts of warming intensified from the RCP 2.6 to the 8.5 emission scenario. Fishing negatively affected demersal and large pelagic fish, which in turn resulted in a biomass increase of forage fish due to a decrease in predation pressure. Water mixing was found to have minor indirect effects on zooplankton biomass and fish. The responses of species and species groups to the combined effects of fishing and warming were approximately equally divided between additive, synergistic and antagonistic. Interpretation of our model results suggests that the southern Benguela system is likely to be affected by climate change, including substantial changes in the abundance of some species important to the region's fisheries. Future planning for fisheries needs to take this into account, including through management that strives to maintain the resilience of key species and the system as a whole. In line with previous studies on the southern Benguela, the results reinforce the importance of including consideration of the indirect and combined impacts of climate change and fishing in management and planning.     

Linking temperate demersal fish species to habitat: scales,patterns and future directions

Adoption of the ecosystem approach to fisheries management relies on recognition of the link between fish and other components of the ecosystem, namely their physical and biological habitat. However, identifying the habitat requirements of marine fishes and hence determining their distribution in space and time is scientifically complex. We analysed the methodologies and findings of research on temperate, demersal fish habitat requirements to highlight the main developments in this field and to identify potential shortfalls. Many studies were undertaken over large spatial scales (≥100s km²) and these generally correlated abundances of fish to abiotic variables. Biological variables were accounted for less often. Small spatial scale (≤m²), experimental studies were comparatively sparse and commonly focused on biotic variables. Whilst the number of studies focusing on abiotic variables increased with increasing spatial scale, the proportion of studies finding significant relationships between habitat and fish distribution remained constant. This mismatch indicates there is no justification for the tendency to analyse abiotic habitat variables at large spatial scales. Innovative modelling techniques and habitat mapping technologies are developing rapidly, providing new insights at the larger spatial scales. However, there is a clear need for a reduction in study scale, or increase in resolution additional to the integration of biotic variables. We argue that development of sound predictive science in the field of demersal fish habitat determination is reliant on a change in focus along these lines. This is especially important if spatial management strategies, such as Marine Protected Areas (MPA) or No Take Zones (NTZ), are to be used in future ecosystem‐based approaches to fisheries management.     

Is fisheries production within Large Marine Ecosystems determined by bottom‐up or top‐down forcing?

Understanding the mechanisms driving fisheries production is essential if we are to accurately predict changes under climate change and exploit fish stocks in a sustainable manner. Traditionally, studies have sought to distinguish between the two most prominent drivers, ‘bottom‐up’ (resource driven) and ‘top‐down’ (consumer driven); however, this dichotomy is increasingly proving to be artificial as the relative importance of each mechanism has been shown to vary through space and time. Nevertheless, the reason why one predominates over another within a region remains largely unknown. To address this gap in understanding, we identified the dominant driver of commercial landings within 47 ecosystems, encompassing a wide range of biogeochemical conditions and fishing practices to elucidate general patterns. We show that bottom‐up and top‐down effects vary consistently with past fishing pressure and oceanographic conditions; bottom‐up control predominates within productive, overfished regions and top‐down in relatively unproductive and under‐exploited areas. We attribute these findings to differences in the species composition and oceanographic properties of regions, together with variation in fishing practices and (indicative) management effectiveness. Collectively, our analyses suggest that despite the complexity of ecological systems, it is possible to elucidate a number of generalities. Such knowledge could be used to increase the parsimony of ecosystem models and to move a step forward in predicting how the global ocean, particularly fisheries productivity, will respond to climate change.     

Keep it simple: three indicators to deal with overfishing

Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, with 100% as target; (ii) percent of specimens with optimum length in catch, with 100% as target; and (iii) percentage of ‘mega‐spawners‘ in catch, with 0% as target, and 30–40% as representative of reasonable stock structure if no upper size limit exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Epinephelus aeneus demonstrate their usefulness. It is argued that such simple indicators have the potential to allow more stakeholders such as fishers, fish dealers, supermarket managers, consumers and politicians to participate in fisheries management and eventually hold and reverse the global pattern of convenience overfishing, which is defined here as deliberate overfishing sanctioned by official bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts.     

Bonga shad (Ethmalosa fimbriata) spawning tactics in an upwelling environment

Successful recruitment in small pelagic fish populations inhabiting upwelling zones is subject to variation in fecundity and is driven by spatial and temporal fluctuations in environmental conditions, that is, mainly sea surface temperature, salinity and food availability. These fluctuations in abiotic factors have stimulated small pelagic fish populations to exhibit specifically adapted spawning tactics. To better understand to what extent a short‐lived exploited fish species such as bonga shad Ethmalosa fimbriata has adapted to an upwelling environment, we have investigated the interrelationship between upwelling intensity as a proxy for productivity and population fecundity by means of a virtual population analysis. We found that females of intermediate size contributed significantly more eggs to the population's fecundity than smaller or larger ones. Our model results further indicate that E. fimbriata exhibits a spawning preference at water temperatures of around 25°C and upwelling intensities of around 2.5 m³ s^?1 m^?1. Hence, we hypothesize that climate change‐driven increases in sea temperatures and modifications of upwelling‐favourable winds could significantly impact the species’ reproductive biology. To understand how climate change might impact fisheries, spawning tactics of small pelagic fishes are important to assess as well as their recruitment success. Such information is particularly relevant in countries where the fishery is critical at socio‐economic level, to better implement fisheries management addressing multiple stressors.     

European small pelagic fish distribution under global change scenarios

The spectre of increasing impacts on exploited fish stocks in consequence of warmer climate conditions has become a major concern over the last decades. It is now imperative to improve the way we project the effects of future climate warming on fisheries. While estimating future climate‐induced changes in fish distribution is an important contribution to sustainable resource management, the impacts on European small pelagic fish—representing over 50% of the landings in the Mediterranean and Black Sea between 2000 and 2013—are yet largely understudied. Here, we investigated potential changes in the spatial distribution of seven of the most harvested small pelagic fish species in Europe under several climate change scenarios over the 21st century. For each species, we considered eight Species Distribution Models (SDMs), five General Circulation Models (GCMs) and three emission scenarios (the IPCC Representative Concentration Pathways; RCPs). Under all scenarios, our results revealed that the environmental suitability for most of the seven species may strongly decrease in the Mediterranean and western North Sea while increasing in the Black and Baltic Seas. This potential northward range expansion of species is supported by a strong convergence among projections and a low variability between RCPs. Under the most pessimistic scenario (RCP8.5), climate‐related local extinctions were expected in the south‐eastern Mediterranean basin. Our results highlight that a multi‐SDM, multi‐GCM, multi‐RCP approach is needed to produce more robust ecological scenarios of changes in exploited fish stocks in order to better anticipate the economic and social consequences of global climate change.     

Extinction vulnerability in marine populations

Human impacts on the world's oceans have been substantial, leading to concerns about the extinction of marine taxa. We have compiled 133 local, regional and global extinctions of marine populations. There is typically a 53‐year lag between the last sighting of an organism and the reported date of the extinction at whatever scale this has occurred. Most disappearances (80%) were detected using indirect historical comparative methods, which suggests that marine extinctions may have been underestimated because of low‐detection power. Exploitation caused most marine losses at various scales (55%), followed closely by habitat loss (37%), while the remainder were linked to invasive species, climate change, pollution and disease. Several perceptions concerning the vulnerability of marine organisms appear to be too general and insufficiently conservative. Marine species cannot be considered less vulnerable on the basis of biological attributes such as high fecundity or large‐scale dispersal characteristics. For commercially exploited species, it is often argued that economic extinction of exploited populations will occur before biological extinction, but this is not the case for non‐target species caught in multispecies fisheries or species with high commercial value, especially if this value increases as species become rare. The perceived high potential for recovery, high variability and low extinction vulnerability of fish populations have been invoked to avoid listing commercial species of fishes under international threat criteria. However, we need to learn more about recovery, which may be hampered by negative population growth at small population sizes (Allee effect or depensation) or ecosystem shifts, as well as about spatial dynamics and connectivity of subpopulations before we can truly understand the nature of responses to severe depletions. The evidence suggests that fish populations do not fluctuate more than those of mammals, birds and butterflies, and that fishes may exhibit vulnerability similar to mammals, birds and butterflies. There is an urgent need for improved methods of detecting marine extinctions at various spatial scales, and for predicting the vulnerability of species.     

Indicators of change in the size structure of fish communities: A case study from the south coast of South Africa

Heavy fishing is believed to change the size structure of fish communities through the differential removal of larger sized individuals and species. The size structure of the demersal fish communities off the south coast of South Africa is assessed using a variety of size-based indicators. The communities on this coast are subjected to different fisheries with wide ranging impacts. Changes in the size structure were assessed over the period from 1986 to 2003 for the whole south coast and two depth strata. There was a reduction in the mean length, mean maximum length (L_max), and proportion of large fish in these fish communities, and a corresponding increase in the proportion of small fish. Species with a large L_max declined in mean catch rate and mean length in contrast to species with a small L_max. The trend in the size-based indicators confirms that there has been a change in the size structure of the communities. This change is characterized primarily by a reduction in the abundance of larger sized individuals and a reduction in species with a large maximum length.     

Essential fish habitats and hotspots of nekto‐benthic diversity and density in the western Mediterranean

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The assessment of fishery status depends on fish habitats

At the crux of the debate over the global sustainability of fisheries is what society must do to prevent over‐exploitation and aid recovery of fisheries that have historically been over‐exploited. The focus of debates has been on controlling fishing pressure, and assessments have not considered that stock production may be affected by changes in fish habitat. Fish habitats are being modified by climate change, built infrastructure, destructive fishing practices and pollution. We conceptualize how the classification of stock status can be biased by habitat change. Habitat loss and degradation can result in either overly optimistic or overly conservative assessment of stock status. The classification of stock status depends on how habitat affects fish demography and what reference points management uses to assess status. Nearly half of the 418 stocks in a global stock assessment database use seagrass, mangroves, coral reefs and macroalgae habitats that have well‐documented trends. There is also considerable circumstantial evidence that habitat change has contributed to over‐exploitation or enhanced production of data‐poor fisheries, like inland and subsistence fisheries. Globally many habitats are in decline, so the role of habitat should be considered when assessing the global status of fisheries. New methods and global databases of habitat trends and use of habitats by fishery species are required to properly attribute causes of decline in fisheries and are likely to raise the profile of habitat protection as an important complementary aim for fisheries management.     

Harvest control rules used in US federal fisheries management and implications for climate resilience

Climate change is altering the productivity of marine fisheries and challenging the effectiveness of historical fisheries management. Harvest control rules, which describe the process for determining catch limits in fisheries, represent one pathway for promoting climate resilience. In the USA, flexibility in how regional management councils specify harvest control rules has spawned diverse approaches for reducing catch limits to precautionarily buffer against scientific and management uncertainty, some of which may be more or less resilient to climate change. Here, we synthesize the control rules used to manage all 507 US federally managed fish stocks and stock complexes. We classified these rules into seven typologies: (1) catch-based; (2) constant catch; (3) constant escapement; (4) constant F; (5) stepped F; (6) ramped F and (7) both stepped and ramped F. We also recorded whether the control rules included a biomass limit (‘cut-off’) value or were environmentally linked as well as the type and size of the buffers used to protect against scientific and/or management uncertainty. Finally, we review the advantages and disadvantages of each typology for managing fisheries under climate change and provide seven recommendations for updating harvest control rules to improve the resilience of US federally managed fisheries to climate change.     

Chum salmon (Oncorhynchus keta) growth and temperature indices as indicators of the year–class strength of age‐1 walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea

Ecosystem‐based fisheries management requires the development of physical and biological time series that index ocean productivity for stock assessment and recruitment forecasts for commercially important species. As recruitment in marine fish is related to ocean condition, we developed proxies for ocean conditions based on sea surface temperature (SST) and biometric measurements of chum salmon (Oncorhynchus keta) captured in the walleye pollock (Gadus chalcogrammus) fishery in the eastern Bering Sea in three periods (July 16–30, September 1–15 and September 16–30). The main purpose of this paper was to evaluate Pacific salmon (Oncorhynchus spp.) growth as a possible indicator of ocean conditions that, in turn, may affect age‐1 walleye pollock recruitment. Marine growth rates of Pacific salmon are the result of a complex interplay of physical, biological and population‐based factors that fish experience as they range through oceanic habitats. These growth rates can, therefore, be viewed as indicators of recent ocean productivity. Thus, our hypothesis was that estimated intra‐annual growth in body weight of immature and maturing age‐4 male and female chum salmon may be used as a biological indicator of variations in rearing conditions also experienced by age‐0 walleye pollock; consequently, they may be used to predict the recruitment to age‐1 in walleye pollock. Summer SSTs and chum salmon growth at the end of July and September explained the largest amount of variability in walleye pollock recruitment indicating that physical and biological indices of ocean productivity can index fish recruitment.     

Using scenarios to project the changing profitability of fisheries under climate change

Over‐exploitation and economic underperformance are widespread in the world's fisheries. Global climate change is further affecting the distribution of marine species, raising concern for the persistence of biodiversity and presenting additional challenges to fisheries management. However, few studies have attempted to extend bioclimatic projections to assess the socio‐economic impacts of climate‐induced range shifts. This study investigates the potential implications of changes in relative environmental suitability and fisheries catch potential on UK fisheries by linking species distribution modelling with cost‐benefit analyses. We develop scenarios and apply a multimodel approach to explore the economic sensitivity of UK fisheries and key sources of uncertainty in the modelling procedure. We projected changes in maximum potential catch of key species and the resulting responses in terms of net present value (NPV) over a 45‐year period under scenarios of change in fuel price, discount rate and government subsidies. Results suggest that total maximum potential catch will decrease within the UK EEZ by 2050, resulting in a median decrease in NPV of 10%. This value decreases further when trends of fuel price change are extrapolated into the future, becoming negative when capacity‐enhancing subsidies are removed. Despite the variation in predictions from alternative models and data input, the direction of change in NPV is robust. This study highlights key factors influencing future profitability of UK fisheries and the importance of enhancing adaptive capacity in UK fisheries.     

The impact of methodological choices on the outcome of national‐level climate change vulnerability assessments: An example from the global fisheries sector

Climate change vulnerability assessments have been receiving increasing attention from policymakers and academics. Given scarce funds for adaptation, the UNFCCC Secretariat has suggested that eligible countries be prioritized for support based on their vulnerability to climate change. National‐level fisheries sector climate change vulnerability assessments as well as other overall vulnerability assessments to date have lent support to the idea that least developed countries (LDCs) are more vulnerable to climate change than small island developing states (SIDS) and other coastal countries. We demonstrate that these perceived differences in vulnerability among country groups are partly due to methodological choices made during these assessments. We argue that national‐level vulnerability assessments, and particularly those dealing with the fisheries sector, often suffer from four main methodological shortcomings: (i) an inconsistent representation of countries belonging to each group, (ii) use of socioeconomic indicators that are not scaled to population size, (iii) use of a small number of indicators and (iv) lack of accounting for potential redundancy among indicators. Building on a previous framework, we show that by addressing the four aforementioned methodological shortcomings, the ranking in fisheries sector vulnerability among SIDS, LDCs and other coastal countries is altered significantly. Our results underscore that the vulnerability of SIDS was partially concealed in previous assessments and suggest that SIDS are in fact the most vulnerable group. Although this study focuses on assessing the vulnerability of the fisheries sector to climate change in SIDS, LDCs and other coastal countries, the implications also apply to other sectors and country groupings.