Stock Collapse Research Articles

Assessing vulnerability of freshwater minnows in the Gangetic floodplains of India for conservation and management: Anthropogenic or climatic change risk?

Minnows are the most ignored yet indispensable group of freshwater fishes in Asian inland waters. The reproductive resilience of minnows facing climatic variability, using a wetland inhabiting species Amblypharyngodon mola (Mola carplets) in lower Indo-Gangetic floodplains, was validated. Results revealed that spawning decision in females (threshold gonadosomatic index ≥ 5 units) is neither cued by water temperature nor rainfall. They can maintain pre-spawning fitness (condition factor 1.12–1.25 units) within a broad temperature (22–33 °C) and rainfall (0–800 mm) window by active feeding, thus no risk of skipped spawning decisions while facing future climatic variabilities. Present breeding phenology (May-December) might have prolonged in the recent decade, especially the tail-end, concomitant with increasingly hot and rainy monsoon (May-August) and warmer post-monsoon months (September-December). Minnows are expected to prosper in a future climatic scenario, contributing to ecosystem balance (algal grazers) and regional food security. Female first maturity (♀ puberty) was encountered at 4.7–5.1 cm total length, hinting at a probable increase in the recent decade. Climate-favored prolonged recruitment window, in absence of extreme fishing pressure (currently), might have led to such pattern. However, this state might be temporary and labile. Minnows may soon get altered to earlier puberty (=warning sign of stock collapse) if fishing pressure intensifies under a reproductively favoring climate progression. Threshold body girth for spawning females was estimated at 3.2–3.4 cm (+17% than non-breeding ones). Fishing nets having mesh sizes (=total circumference) at least > 32–34 mm will most likely be the key to minnows’ endurance or survival in the coming decades.

Les défis mondiaux à venir en 2020 et 2021, 2022

We are living, according to Naomi Klein, a very effective Worldwide Shock Strategy. Indeed, after the covid19 crisis, we could be confronted with an important economic collapse of Banks, moneys, and stock markets. Governments will probably be obliged to install a “Basic Income” for the poorest citizens. To create new money systems for companies and for citizens. And to promote culture in a new and very powerful way. We will also discover after this collapse, that the new circular economy is already functioning very well.
 Two scenarios are possible. 1. An extreme but soft political control of the citizens, “Chinese way”. And the scenario 2 will be a very important paradigm shift, towards a higher level of consciousness, with a new spiritual dimension. This second scenario becomes more and more possible.

Economic development in times of population decline—a century of European eel fishing on the Swedish west coast

Abstract The European eel stock is in a multi-decadal decline. When fishing yield diminished throughout Europe, the small-scaled fyke-net fishery for eel on the west coast of Sweden gradually increased. This contrary trend lasted from the early-1900s, until the 1990s when fishing restrictions eventually limited the catch. We identified the processes driving this aberrant historical development. Using data on the fisheries from 1914 to 2006, we analysed the relation of total landed quantities to stock abundance indices, weather conditions, technical development, and market indicators. No relation between landed volumes and abundance indices was found, but market price (inflation-adjusted) was clearly correlated. Weather and technical development had a minor influence on landed volumes. This indicates that the commercial eel fishery on the west coast developed due to increasing demand and increasing eel prices. We found no evidence that the local stock has been fully exploited, though the increasing catch must have gradually reduced the contribution to the international spawning stock. These results stress the importance of considering economic processes when interpreting historical catch data as a source of information on population size in stock assessments, and ultimately, understanding the collapse of the eel stock.

From Membership to Partnership The EU and Its Relations with the UK After Brexit: The Fisheries Dimension

Fishing in European waters has been a contentious issue since the sixteenth century and was a key factor in the development of the international law of the sea itself. At the time the UK joined the EU and shared its waters with Member State vessels it also lost access to its traditional fishing grounds off Iceland. The Common Fisheries Policy developed a centralized approached based around historic fleet size rather than productivity of Member States’ waters. Controls were centred around technical measures, reduction in capacity and quota. These worked: the collapse of fish stocks was halted and started to recover a little. However many stocks are still potentially illegally allocated beyond scientific levels, and fishing continues unmanaged in the EU’s suite of offshore marine protected areas. The management institutions need greater transparency and stronger adherence to the law. There is scope to build a future relationship between the EU and the UK: the UK and some of its overseas territories need the EU market, many stocks are shared, and the parties will need to agree on scientific approaches. However, It is likely that the UK is due a greater allocation of stocks than the current system. As we approach the endgame of the Brexit negotiations it is important that both sides reflect that fishing represents less that 0.1% of their economies and over-politicization of a small sector will not help either party in the context of the larger negotiations. The Common Fisheries Policy (CFP), which the UK helped to create, has started to rebuild stocks and that upward trajectory needs to continue; it will only do so through collaboration. Brexit, Fisheries, Competence, Environment

Optimal shape of the harvest control rule for different fishery management objectives

Abstract To determine the optimal shape of the harvest control rule (HCR) achieving common fisheries management objectives (maximizing the average catch, reducing the deviation of yields, and avoiding stock collapse) and ensure robustness to observation errors, we estimate the optimal values of biological reference points (BRPs) composing the HCR. While traditional HCRs usually consist of three BRPs based on the fishing mortality coefficient (F3-HCR), we introduce an alternative HCR defined by 21 BRPs based on the catch levels (C21-HCR) to cover various possible shapes of HCR including smooth ones. We compare the shape and the performance between the optimal C21-HCR and the optimal F3-HCR and conclude that the optimal HCR can be composed of the gradual combination of the basic strategies: the constant escapement strategy, the constant harvest rate (CHR) strategy, and the constant catch strategy. However, the current F3-HCR does not necessarily allow this combination and generally returns lower performance levels than the optimal C21-HCR (since the basic strategy is confined to CHR) excluding the range of low biomass. This result will provide a clear perspective to improve HCR according to the magnitude of assessment errors and to compromise multiple fisheries management objectives when various stakeholders are involved.

Challenges and possible impacts of artisanal and recreational fisheries on tigerfish Hydrocynus vittatus Castelnau 1861 populations in Lake Kariba, Zimbabwe

Increased fishing pressure from artisanal and recreational fishing has led to the collapse of some important fish stocks around the world over the past years. There is currently limited understanding of the impacts of recreational and artisanal fishing on tigerfish Hydrocynus vittatus populations in Lake Kariba and the socioeconomic factors behind them. Hence, this study investigated socioeconomic factors that act as drivers of the recreational and artisanal fishery industry and what sort of impact this would likely have on tigerfish H. vittatus populations using qualitative approaches. Eight three percent of the artisanal fishers interviewed recorded high catches during the summer season (October–February), which also coincides with the breeding season for tigerfish when it migrates up the rivers. Recreational anglers mainly caught females during the tigerfish tournament which is likely to have a significant effect on the tigerfish population in the long term through changes in tigerfish recruitment and other life history traits. Tigerfish size at sexual maturity and catch per unit effort which are all indicators of overexploitation were found to have decreased over the past years. Results further demonstrated increased fishing activities from artisanal and recreational fishing. It can be implied that the population of tigerfish may inadvertently be affected, but direct evidence that both recreational and artisanal fishing were having impacts on tigerfish populations was limited. It is therefore recommended that effective conservation measures such as preventing fish poaching during the tigerfish breeding season are put in place to protect the population and that of other fishes (i.e. potential prey).

Fluidigm's Survival Battle: Turnaround in the Midst of a Genomics Revolution

This field-based case uses the challenges facing Fluidigm Corporation, a publicly traded biotechnology company, to explore and analyze innovation-driven growth. Facing a number of headwinds product backorders, strong competition, declining product demand, missed earnings, and an 87% stock collapse over 10 months new CEO Chris Linthwaite needs to devise and share his turnaround strategy with the board of directors. He could recommend launching a new product, reallocating and reprioritizing R&D spend, cutting administrative costs, acquiring a new company or technology, or restructuring the company's capital structure. Which choice will lead to the quickest path back to profitability while driving long-term value creation for its various stakeholders? The case provides an opportunity to explore the tensions between short-run viability and long-run R&D and innovation. Excerpt UVA-S-0339 Rev. Jan. 26, 2021 Fluidigm's Survival Battle: Turnaround in the Midst of a Genomics Revolution Introduction When new CEO Chris Linthwaite sat down at his desk at Fluidigm Corporation (Fluidigm) for the first time in August 2016, he could almost feel the walls burning around him. Fluidigm, a biotechnology company based in south San Francisco, had started out as a promising genomics start-up in 1999 but had experienced rough times in recent years. Following a year of missed earnings in 2015, strong currency headwinds, product backorders, strong competition, and a lag in product demand, the market had finally borne all it could bear, and Fluidigm's stock had collapsed 87% in 10 months, from a high of 43.97 in April 2015 to a low of 5.83 in February 2016 (Exhibit1). Fluidigm was burning through cash and had posted yet another quarter of losses (Exhibits2 and 3). In addition to the street doubting Fluidigm's capabilities, employee morale had plummeted and the company had mounting cash flow issues. In mid-October 2016, more disappointing Q3 results were just about to become public. Fluidigm had missed its earnings again, and Linthwaite was preparing his turnaround strategy to present to his board of directors tomorrow. Recognizing that he had multiple stakeholders to please and many levers he could pull to right the ship, he wondered where he should start. . . .

Biological perspectives on complexities of fisheries co-management: A case study of Newfoundland and Labrador snow crab

A thrust toward fisheries co-management systems occurred globally throughout the 1990s. This was partially influenced by the collapse of groundfish stocks including the iconic northern cod and other fisheries resources in Newfoundland and Labrador (NL). The management system for NL snow crab burgeoned during this period, largely in the absence of biological information for the resource. There is a high volume of theoretical literature advocating for the benefits of fisheries co-management, but little documented perspectives from fisheries scientists actively engaged in such management systems, nor literature detailing how co-management regimes could affect scientific research or assessment programs. In this paper, in context of a large fishery, we provide specific examples of how co-management processes can influence scientific research and monitoring programs and the biological functioning of important marine resources. We undertake critical evaluation on topics including spatial scales of management, fishery timing, fishery closures, collaborative research, and harvester perceptions of stock size. We conclude there are both scientific advantages and disadvantages to operating within co-management systems, but that the NL snow crab management system has evolved to promote processes problematic to provision of the best possible science advice. We conclude that adaptive co-management measures are required to address several current challenges in order to maximize scientific value within this system. In general, the paper demonstrates how flexibility is needed by all partners involved in resource co-management systems to adapt to fundamental scientific principles inherent in changing methodologies and the generation of knowledge.

Dying, Decaying, and Dissolving into Irrelevance: First Direct in-the-Field Estimate of Crassostrea virginica Shell Loss—a Case History from Mississippi Sound

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure.

Cooperative and non-cooperative behaviour in the exploitation of a common renewable resource with environmental stochasticity

Classical fisheries biology aims to optimise fisheries-level outcomes, such as yield or profit, by controlling the fishing effort. This can be adjusted to allow for the effects of environmental stochasticity, or noise, in the population dynamics. However, when multiple fishing entities, which could represent countries, commercial organisations, or individual vessels, can autonomously determine their own fishing effort, the the optimal action for one fishing entity depends on the actions of others. Coupled with noise in the population dynamics, and with decisions about fishing effort made repeatedly, this becomes an iterated stochastic game. We tackle this problem using the tools of stochastic optimisation, first for the monopolist’s problem and then for the duopolist’s problem. In each case, we derive optimal policies that specify the best level of fishing effort for a given stock biomass. Under these optimal policies, we can calculate the equilibrium stock biomass, the expected long-term return from fishing and the probability of stock collapse. We also show that there is a threshold stock biomass below which it is optimal to stop fishing until the stock recovers. We then develop an agent-based model to test the effectiveness of simple strategies for responding to deviations by an opponent from a cooperative fishing level. Our results show that the economic value of the fishery to a monopolist, or to a consortium of fishing agents, is robust to a certain level of noise. However, without the means of making agreements about fishing effort, even low levels of noise make sustained cooperation between autonomous fishing agents difficult.

Can multi‐species shark longline fisheries be managed sustainably using size limits? Theoretically, yes. Realistically, no

Abstract Size limits are a common fisheries management strategy that are applied to many fisheries and species. Most size limits use a minimum legal size to protect adult fish as per the ‘reproduce at least once’ paradigm, where stock collapse becomes impossible if every adult can produce one spawner prior to harvest. These approaches can be useful in fisheries where determining catch is difficult and therefore catch limits can be ineffective and potentially cause stock decline. Shark longline fisheries can be complicated to manage due to a deficiency of species‐level reporting. Catch limits are therefore difficult to determine, creating a need for other management measures. Here, three different size‐based management approaches were tested using the shark longline fishery from Papua New Guinea as a case study. These approaches included minimum size, maximum size and harvest slot approaches. Age‐structured Leslie matrix models revealed a broad range of productivities for 12 commonly caught species, ranging from low population growth rates of 1% per year for pelagic thresher sharks Alopias pelagicus to >33% per year for blue sharks Prionace glauca. Therefore, different harvest strategies were required for each species to be fished sustainably. However, management could be applied by grouping similar and easily distinguishable groups of species together. Synthesis and applications. The most pragmatic harvest strategy for all shark species included in this study was to limit harvest to mature individuals using minimum legal sizes. This provided sufficient resilience for all species to tolerate higher levels of fishing mortality than the Papua New Guinea (PNG) longline fishery could impose. Legal minimum lengths were derived from the largest length‐at‐maturity within each species group. However, while this produced a sustainable harvest strategy, issues with selectivity, post‐release mortality, interactions with other fisheries, economic viability and illegal, underreported and unregulated fishing were challenges to restricting fishing to the correct size classes and overall management efficacy. Therefore, while theoretically viable harvest strategies were outlined, it is apparent that size limits would not ensure that these shark species are fished sustainably. Therefore, the PNG longline fishery cannot operate sustainably if it were to reopen using size limits as its sole management strategy.

Linking the performance of a data-limited empirical catch rule to life-history traits

AbstractWorldwide, the majorities of fish stocks are data-limited and lack fully quantitative stock assessments. Within ICES, such data-limited stocks are currently managed by setting total allowable catch without the use of target reference points. To ensure that such advice is precautionary, we used management strategy evaluation to evaluate an empirical rule that bases catch advice on recent catches, information from a biomass survey index, catch length frequencies, and MSY reference point proxies. Twenty-nine fish stocks were simulated covering a wide range of life histories. The performance of the rule varied substantially between stocks, and the risk of breaching limit reference points was inversely correlated to the von Bertalanffy growth parameter k. Stocks with k>0.32 year−1 had a high probability of stock collapse. A time series cluster analysis revealed four types of dynamics, i.e. groups with similar terminal spawning stock biomass (collapsed, BMSY, 2BMSY, 3BMSY). It was shown that a single generic catch rule cannot be applied across all life histories, and management should instead be linked to life-history traits, and in particular, the nature of the time series of stock metrics. The lessons learnt can help future work to shape scientific research into data-limited fisheries management and to ensure that fisheries are MSY compliant and precautionary.

Recruitment variability in Baltic flounder (Platichthys solemdali) – effects of salinity with implications for stock development facing climate change

The brackish water Baltic Sea is strongly influenced by irregular saline water inflows. Fewer inflow events since the 1980s have resulted in a decrease in salinity, and will according to predicted climate change continue to decrease. The newly described Baltic flounder Platichthys solemdali has adapted to reproduction at low salinity conditions since it colonized the Baltic Sea 7000 years BP; in the area studied (ICES SD 3d 28.2) spawning occurs at 3–20 m depth at ca 7 psu. Here we monitored variability in year-class strength as newly settled 0-gr fish in three coastal nursery areas, and compared obtained recruitment indices with prevailing temperature and salinity conditions. 0-gr abundance indices varied considerably between years, from 1 to 90, 10–296 and 17–86 at the respective sampling site, and showed strong accordance with the age structure of the adult stock. Variability in temperature showed no effect, but stronger and weaker year-classes respectively were related to variability in salinity in the range 6.6–7.1 psu with stronger year-classes at >6.8 psu. This coincides with variability in spermatozoa motility, fertilization rates and early egg development at different salinities and suggests that the year-class strength may be set already at the egg stage. Thus, only small changes in salinity at spawning may affect reproductive success and ultimately stock development. The potential effects on stock abundance and distribution facing climate change call for changes in future fishing patterns as well as adaptations in management to prevent stock collapse.

Long-Term Stability in the Trophic Ecology of a Pelagic Forager Living in a Changing Marine Ecosystem

Natural or human-induced environmental changes can modify the structure of ecological communities and thus alter food web interactions. After the collapse of hake stocks (Merluccius hubbsi) provoked by fisheries over the Patagonian shelf in 1997 profound changes have taken place in the community, including long-term dietary shifts in some marine vertebrate predators. Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in bone collagen of subadult and adult male South American fur seals (Arctocephalus australis) were measured for the period 1976-2017 to investigate if the changes occurred in the marine community from northern and central Patagonia affected the diet of this predator. Suess corrected δ13C values and δ15N values in bone collagen of fur seals did not change significantly over the study period. According to this, male fur seals have remained as pelagic foragers without changing their trophic position nor switching their main preys in the Patagonian food web over the last four decades. This long-term stability in the diet of fur seals contrasts with dietary changes reported for benthic foragers in the region. Although long-term diet studies are restricted to a few marine predators in the region, current evidence suggests that benthic-demersal foragers were more prone to dietary shifts than pelagic ones after perturbations that occurred in the marine community of northern and central Patagonia.

Modeling the Scenarios of Collapse of the Commercial Aquatic Populations off the Coast of Canada and Alaska*

Special situations, which are difficult to predict and to model by traditional methods, develop rapidly in population processes. A sudden collapse of commercial fish stocks, in addition to outbreaks of forest pests, are among the most economically significant nonlinear phenomena in ecosystems. According to systems analysis of statistical data on the dynamics of catches, the transitional stages of rapid degradation in completely different species of fish and aquatic invertebrates occur in a similar way. The most representative stages of the development of fish resources collapse have been distinguished. Restoration of the already critically depleted aquatic bioresources occurs at different rates. Based on the method of dynamically redefinable hybrid computational structure, we considered situations of collapse that occurred with crab off the coast of Alaska and northern cod off the coast of Canadian provinces of Newfoundland and Labrador. The resulting computational scenarios for collapse manifestation consist of three stages, all the way up to the degradation of bioresources. Bifurcations are implemented purposefully and follow the logic of the process. The modeling method is generalized for cases with stationary food resources and with oscillatory dynamics of food organisms.

Assessing drivers of tropical and subtropical marine fish collapses of Brazilian Exclusive Economic Zone

Overfishing is a concerning threat that can lead to the collapse of fish stocks. We assessed the combinations of factors, including biological traits, types of exploitation and responses to sea temperature and salinity changes, that drive species to collapse in the Brazilian Exclusive Economic Zone (EEZ) tropical and subtropical regions. We applied a catch-based method of stock classification and a catch time series of 61 years from 132 exploited fish species. Species were categorized as Collapsed, Overexploited, Fully Exploited or in Development, and we used a GAM analysis to understand their categorization over time. Furthermore, a Redundancy Analysis was developed to assess the species characteristics that best predicted each exploitation category. Twelve species were classified as Collapsed, 55 as Overexploited, 46 as Fully Exploited and 19 as in Development. Tropical and subtropical exploited species collapses in Brazil were best explained by a complex combination of a negative impact of warmer sea temperatures, fishery exploitation and specific life-history traits. A synergistic interaction between these factors could bring species to collapse. We hypothesize that the exploitation of species with vulnerable traits may alter how these species respond to temperature and, therefore, lead them to collapse given that intense exploitation may affect their ability to respond to temperature increases. Measures to mitigate climate change impacts should take into consideration incentives to decrease the exploitation of vulnerable species and, specifically, consider species with more sensitive biological traits. Such measures are also important to minimize the socioeconomic impacts on the people that depend on these species.

A review of the biology and culture of two emerging aquaculture species in Nigeria, the <i>Papyrocranus afer</i> and <i>Xenomystus nigri</i>

A review was carried out on two emerging local species, with the potential of being of enormous economic importance in the Ornamental Fishery Industry in Nigeria, the Papyrocranus afer and Xenomystus nigri, of the family Notopteridae. This study is aimed at providing knowledge on these two locally available aquarium fishes, in order to encourage their breeding/large scale culture, for sustainable growth and development of the Ornamental Fishery Industry in Nigeria. The available information on the biology, including the distribution, environmental and nutritional requirements, reproductive behavior, and culture of these two species were documented. The potential prospects and challenges in the breeding/culture of these species, were also noted however, not much is available as regards their breeding/culture, although these species are of great Ornamental importance due to their characteristic features, pointing to the fact that, when they were needed, they were sourced from the wild. Thus, there is dire need to breed/culture these species in order to fully harness their economic potentials and prevent the collapse of wild stock, in Nigeria.Keywords: breeding, culture, notopteridae, ornamental importance, papyrocranus afer, xenomystus nigri

Fecundity of haddock (Melanogrammus aeglefinus) off southern Newfoundland

Reproductive life history parameters, such as size-specific fecundity, can contribute to our understanding of fish population dynamics. However, most of these parameters are difficult or time-consuming to obtain. Therefore, previously calculated parameters are often used in combination with more easily collected metrics of size. Significant temporal variation in fecundity is known to occur in many fish species, meaning that previous estimates may be unreliable when examining contemporary fish stocks. For southern Newfoundland haddock, the only published fecundity data were collected more than 50 years ago when this species supported a major fishery in the area. Here we present fecundity data collected during the 1960s immediately following stock collapse, as well as data from 2013 to 2014 (after 20 years of a fishing moratorium) and examine potential differences in egg production among the time periods. Contemporary estimates of haddock fecundity were more similar to estimates of fecundity immediately following stock collapse than estimates during the period of maximum exploitation. Additionally, comparison of haddock fecundity throughout the northwest Atlantic Ocean revealed contemporary estimates from southern Newfoundland to generally be higher than those from the Scotian Shelf for haddock at all lengths as well as greater than those from George’s Bank until about 60 cm in total length. The ability of various fish characteristics (length, weight, age, and condition) to serve as metrics of haddock fecundity were investigated and found that while length was the best predictor of fecundity, explanatory power was relatively low (maximum R2 = 0.37), and there was little to no effect of fish condition on fecundity. Inter-annual variability in fecundity estimates, coupled with the lack of a suitable proxy for fecundity for Newfoundland haddock suggests that ongoing monitoring is required to accurately estimate reproductive potential.

Temperature influences on growth of unfished juvenile Northern cod (Gadus morhua) during stock collapse

AbstractThis study examined growth of unfished juvenile Northern cod (Gadus morhua) off Newfoundland concomitant with stock collapse in the cold early 1990s. Two unpublished data sets were examined, one from collapse‐period trapping sites along the northeast coast of Newfoundland and one from a post‐collapse inshore trawl survey. Cumulative surface and bottom temperatures were significant predictors of growth rates of the young fish with year‐classes born during collapse experiencing slower growth than those born during subsequent warming. Relationships between accrued temperature and growth were consistent across periods, with slow growth of collapse‐period fish reflecting slower accumulation of temperature‐at‐age. Temperature influences were spatially broad‐based with no significant differences in growth rates for fish captured along the entire northeast coast of Newfoundland. Predicted differences in growth rates for collapse versus recovery year‐classes were proportional to cumulative surface temperatures but not cumulative bottom temperatures. Although significant, temperature effects on growth were relatively unimportant at youngest ages. Overall, growth differences between periods were small but large differences occurred between slowest and fastest growing year‐classes. The results suggest initial responses to increasing temperatures were delayed following collapse. We conclude that although temperature was an important determinant of dampened productivity that it alone cannot account for the collapse and slow recovery of the stock. This is the first known study to directly quantitatively link temperature impacts to an unfished component of the Northern cod stock complex during collapse, removing need for implicit assumptions about whether or not cold conditions contributed to the collapse of this iconic fish stock.

Profit and equity trade‐offs in the management of small pelagic fisheries: the case of the Japanese sardine fishery*

The management of small pelagic fisheries is difficult due to environmental regime changes that generate multi‐decadal cyclic fluctuations in stock abundance. Lagged management responses to environmental factors can amplify the effects of fishing and may even result in stock collapse. In this paper, we develop an age‐structured bioeconomic model to explore the effectiveness of alternative management approaches for cyclically fluctuating small pelagic fish stocks. The fishery outcomes are evaluated against the overall profit of the fishery and the intertemporal distribution of fishing profits. The model is parameterised for the Japanese sardine fishery, once the largest fishery in Japan, which has experienced a prolonged period of stock collapse over the last 100 years. The results show that the duration of fishery collapse is mostly determined by the extent of cyclic fluctuations in the recruitment of immature sardines, but the effects of the fluctuations on the fishery are heightened by the cumulative impact of fishing. We further show that restricting fishing reduces the fishery’s overall profits, but smooths the intertemporal distribution of profits, resulting in greater intergenerational equity. This income smoothing effect is particularly pronounced when the stock exhibits high levels of cyclic fluctuations.