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Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size‐structure and potential yields of marine fishes. Previous studies based on mechanistic size‐based food web models have found that bottom‐up processes are important drivers of size‐structure and fisheries yield in changing climates. However, we know less about the joint effects of 'bottom‐up' and physiological effects of temperature; how do temperature effects propagate from individual‐level physiology through food webs and alter the size‐structure of exploited species in a community? Here, we assess how a species‐resolved size‐based food web is affected by warming through both these pathways and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size‐structure, and relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4‐NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature‐effects on physiology in addition to on basal productivity, projected size‐at‐age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size‐at‐age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in decline in the abundance of larger fish and hence spawning stock biomass. These results suggest that to understand how global warming affects the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for. [ABSTRACT FROM AUTHOR]

Emergy analysis is a thermodynamically based approach to assess the performance of systems and it is a useful tool for environmental decision-making. The kelp resource (Lessonia nigrescens Bory) is the basis for one of the main benthic fisheries of northern Chile, in both economic and social terms. The Atacama coastal kelp fishery is most important at the national level. To better understand the long-term changes in the environmental and socioeconomic factors that govern the sustainability of the resource, emergy synthesis was used to evaluate the performance of the L. nigrescens kelp fishery, based on data from 2000, 2014, and 2018. These emergy assessments show that over this period, the empower base (R) supporting intertidal kelp beds decreased 41%, the annual emergy used in the fishing effort (F) increased by an order of magnitude, and the total emergy used in the fishing system (Y) decreased by 39%. The values of the Landings/Fishing Effort Ratio (EYR) showed a general tendency to decrease, as the Emergy Investment Ratio (EIR) increased. The economic exchange of emergy indicates that in 2014 the extractors/collectors operating the algae fishery obtained the greatest emergy gain by trading. The analysis of the emergy indicators explained the long-term changes in the sustainability of the kelp resource and the emergy balance of the economic transactions over the last 20 years. In addition, the emergy evaluation results can be used as a complement to traditional planning methods, to design and implement system-based, resource management measures to ensure a sustainable and healthy kelp fishery. [ABSTRACT FROM AUTHOR]

Since 2013, the pelagic zone of Upper Lake Constance (ULC) has been subject to a massive invasion of the non-native three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758). Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) were used to compare weight-at-age and abundance of pelagic whitefish for years before (1997-2012) and after the invasion (2013-2015). Growth and abundance of pelagic whitefish is shown to be heavily influenced by stickleback presence. Mean autumn weight-at-age of whitefish decreased by 33.3% after the invasion took place and a significant decline in autumn CPUE in otherwise unfished cohorts of the population was also recorded. The results imply direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth and survival, and predation of eggs and larvae, hampering recruitment. These observations coincide with a sharp decline in whitefish yield. In conclusion, this study shows that the invasion of stickleback has substantially altered the pelagic fish community of ULC, with severe consequences for commercial fisheries. [ABSTRACT FROM AUTHOR]

Abstract: Forage fish populations support large scale fisheries and are key components of marine ecosystems across the world, linking secondary production to higher trophic levels. While climate‐induced changes in the North Sea zooplankton community are described and documented in literature, the associated bottom‐up effects and consequences for fisheries remain largely unidentified. We investigated the temporal development in forage fish productivity and the associated influence on fisheries yield of herring, sprat, Norway pout and sandeel in the North Sea. Using principal component analysis, we analysed 40 years of recruitment success and growth proxies to reveal changes in productivity and patterns of synchroneity across stocks (i.e. functional complementarity). The relationship between forage fish production and Calanus finmarchicus (an indicator of climate change) was also analysed. We used a population model to demonstrate how observed shifts in productivity affected total forage fish biomass and fisheries yield. The productivity of North Sea forage fish changed around 1993 from a higher average productivity to lower average productivity. During the higher productivity period, stocks displayed a covariance structure indicative of functional complementarity. Calanus finmarchicus was positively correlated to forage fish recruitment, however, for growth, the direction of the response differed between species and time periods. Maximum sustainable yield (MSY) and the associated fishing mortality (Fmsy) decreased by 33%–68% and 26%–64%, respectively, between the higher and lower productivity periods. Synthesis and applications. The results demonstrate that fisheries reference points for short‐lived planktivorous species are highly dynamic and respond rapidly to changes in system productivity. Furthermore, from an ecosystem‐based fisheries management perspective, a link between functional complementarity and productivity, indicates that ecosystem resilience may decline with productivity. Based on this, we advise that system productivity, perhaps monitored as forage fish growth, becomes an integral part of management reference points; in both single species and ecosystem contexts. However, to retain social license of biological advice when fish catch opportunities are reduced, it is crucial that shifts in productivity are thoroughly documented and made apparent to managers and stakeholders. [ABSTRACT FROM AUTHOR]

In this paper, I argue that we have at hand what is needed to provide scientific advice for ecosystem-based management of small pelagics and other species groups now. The ingredients for this advice are (i) large marine ecosystems as spatial management units; (ii) maintaining ecosystem productivity and exploiting at multispecies maximum yield as overarching management objectives; (iii) assessment of ecosystems by evaluating changes in primary productivity; (iv) an operational management procedure in which single-species catch proposals are adjusted to ecosystem productivity using a set of control rules. Inspection of historic landings for small pelagics and other small species in the Northeast Atlantic (ICES area) reveals that most likely fisheries exploitation does not, and never did, exceed system productivity in most LMEs and is therefore overall sustainable, although not necessarily for individual stocks. [ABSTRACT FROM AUTHOR]

The oceans provide food, employment and income for billions of people. Using data from scientific stock assessments and a statistical model for other fish stocks the past and present status, and the potential catch, abundance and profit for 4713 fish stocks constituting 78% of global fisheries are estimated. Three major scenarios of future trends are considered; business as usual (BAU) in which largely unmanaged fisheries move towards bioeconomic equilibrium but where well-managed fisheries maintain their management, maximum sustainable yield (MSY) in which fisheries are managed to maximize yield, and fisheries reform (REF) where the competitive race to fish is eliminated and fisheries are managed to maximize profit. The future prospects differ greatly based on region of the world and product type. This analysis forecasts that yield in major tuna and forage fish species will remain roughly the same as current levels under all three scenarios, while there does appear to be potential for increased yield of whitefish. There is considerable room for increased profit in most of these fisheries from better management. Increased yield will come from rebuilding overexploited stocks, reducing fishing mortality on stocks that are still abundant but fished at high rates, and surprisingly from fishing some stocks harder. Indeed in Europe and North America the primary potential for increased yield comes from fully exploiting stocks that are now lightly exploited. Asia provides the greatest opportunity for increased fish abundance and increased profit by fisheries reform that would lead to reduced fishing pressure. [ABSTRACT FROM AUTHOR]

Substantial declines in growth and recruitment of lake whitefish ( Coregonus clupeaformis ) and changes in key density-dependent relationships since the 1990s have raised concerns about the effects of these changes on valuable commercial fisheries in Lake Huron. There is evidence for lake whitefish in the southern main basin of Lake Huron that growth and recruitment rates have been reduced by up to 50%. Using a life history model parameterized from fishery-independent survey data for lake whitefish, we investigated the effects of declines in growth and recruitment rates on population dynamics and sustainable harvest. We evaluated a baseline scenario characterized by high growth and recruitment rates, an alternative scenario with a reduced growth rate, and another alternative scenario in which both growth and recruitment rates were reduced. Yield consistently declined by at least 71% in both alternative scenarios compared to the baseline scenario. Also, fishing became unsustainable when both growth and recruitment rates were reduced and the maximum instantaneous fishing mortality rate exceeded 0.5. Our results suggest that the recent reductions in growth and recruitment observed in Lake Huron are of sufficient magnitude to alter productivity and reduce how much can be sustainability harvested from these stocks. [ABSTRACT FROM AUTHOR]

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Managing fisheries resources to maintain healthy ecosystems is one of the main goals of the ecosystem approach to fisheries ( EAF). While a number of international treaties call for the implementation of EAF, there are still gaps in the underlying methodology. One aspect that has received substantial scientific attention recently is fisheries-induced evolution ( FIE). Increasing evidence indicates that intensive fishing has the potential to exert strong directional selection on life-history traits, behaviour, physiology, and morphology of exploited fish. Of particular concern is that reversing evolutionary responses to fishing can be much more difficult than reversing demographic or phenotypically plastic responses. Furthermore, like climate change, multiple agents cause FIE, with effects accumulating over time. Consequently, FIE may alter the utility derived from fish stocks, which in turn can modify the monetary value living aquatic resources provide to society. Quantifying and predicting the evolutionary effects of fishing is therefore important for both ecological and economic reasons. An important reason this is not happening is the lack of an appropriate assessment framework. We therefore describe the evolutionary impact assessment ( Evo IA) as a structured approach for assessing the evolutionary consequences of fishing and evaluating the predicted evolutionary outcomes of alternative management options. Evo IA can contribute to EAF by clarifying how evolution may alter stock properties and ecological relations, support the precautionary approach to fisheries management by addressing a previously overlooked source of uncertainty and risk, and thus contribute to sustainable fisheries. [ABSTRACT FROM AUTHOR]

While management according to biological reference points is well established for many commercial marine fisheries, similar systems for more leisure based fisheries for freshwater fishes are less common. This paper describes the scientific foundation for management according to conservation limits and management targets for Norwegian populations of Atlantic salmon, a highly valued and heavily exploited anadromous fish species. Based on stock recruitment relationships during the freshwater phase, the biomass of females necessary to attain the carrying capacity (yielding average maximum recruitment) has been established as conservation limits for each of the 439 Norwegian populations. Using a simulation model based on reported catch and estimates of exploitation rates, the probability and percentage attainment of the conservation limits have been assessed annually since 2008, and exploitation advice provided for 176 of the largest populations. The number of populations that attained their conservation limits increased substantially after the new management scheme was introduced, despite that the number of returning salmon remained at historical low levels. Overall the populations evaluated in 2011 were at 95% of their conservation limits compared to 91% in 2008 and 85% in 2005. The improvement could largely be attributed to reduced exploitation rates, due to new restrictions in both the marine and river fisheries. The new management scheme also improved the catch statistics and stimulated data acquisition for management. Implementation of management according to conservation limits has been a success in terms of attaining the main management goal of protecting the Atlantic salmon populations by ensuring that an increasing number of the populations likely are at their maximum reproductive capacity. Long-term increases in fisheries yield, the secondary management goal, are likely to be attained, but remain to be documented. Reference point based management of Atlantic salmon exemplifies management within the intersection of fisheries management and conservation biology, borrowing principles from both sides. [ABSTRACT FROM PUBLISHER]

The article presents a study which investigates the relationship between primary productivity (PP) and fish yield from satellite observations and 14 selected large marine ecosystems (LMEs). It states a neural network global model was used to obtain regional PP estimates in each of the 14 LME and yield data were gathered from the Sea Around Us Project (SAUP) catch database. Correspondence analysis were performed on gathered yield data to outline the roles provided by different trophic levels (TLs). Details related to bottom-up control and to-down control as main models to describe marine ecosystems dynamics is provided. New insights into the PP and fisheries relationship which suggests that fish yields can be linked to PP temporal variability than to PP average values is also discussed.

The increase in fisheries yield in the Kattegat during the last four decades can be correlated with a concomitant increase in annual primary production in the region. However, this correlation does not necessarily indicate cause and effect. Other changes have occurred during this period that may also affect fisheries yield (changes in fishing effort, market demand, fleet composition, etc.). This paper examines some of these factors in an effort to identify the underlying cause(s) of the observed increase in fisheries yield. It is concluded that, although there have been major changes in the structure of the fishing fleet and fishing effort in the Kattegat during this period, the observed increase in fisheries yield probably reflects, at least in part, a real increase in fish biomass. It is not possible to document a direct link between this suspected increase in biomass and an increase in primary production. It is, however, noted that the changes in the relative proportion of benthic to pelagic species in the fishery are consistent with the changes which are predicted to occur following an increase in primary production. [ABSTRACT FROM PUBLISHER]