Stock Collapse Research Articles

No more detectable fishing effect on Northern Gulf of St Lawrence benthic invertebrates

Abstract Trawling has been reported worldwide to alter seabed structure, and thus benthic habitats and ecosystems. Usually, a decrease in species richness and biomass is observed, and community structure is modified towards more opportunistic species. The Gulf of St Lawrence (Canada) has been intensely exploited since the 17th century, including net, longline, dredge and trawl fishing activities. Recently, the collapse of groundfish stocks induced a shift in fishing practices toward shrimp trawling, which is currently considered a sustainable fishing activity in the region. However, no long-term study has evaluated the potential effects of trawling disturbances on benthic mega-invertebrates. We investigated whether shrimp trawling had long- (ca. 20 years), mid- (ca. 10 years), and short-term (ca. 4 years) impacts on benthic mega-invertebrate taxa richness, biomass, and community structure. Scientific and fishery trawling data analyses showed that no significant long-, mid-, or short-term effect was detected on taxa richness. Significant but weak effects on biomass and community structure were detected at the mesoscale, i.e. at the scale of fishing grounds. In this long-exploited ecosystem, we suggest that a critical level of disturbance was attained by the first gear passages, which occurred decades ago and had irreversible impacts on the seabed by removing vulnerable taxa and structures that provided three-dimensional habitats. It is likely that benthic communities have subsequently reached a disturbed state of equilibrium on which current trawling disturbance has limited or no further impacts.

Stochastically Induced Critical Depensation and Risk of Stock Collapse

AbstractThis article investigates the risk of stock collapse due to stochastically induced critical depensation in managed fisheries. We use a continuous-time surplus production model and an economic model with downward-sloping demand and stock-dependent costs. First, we derive an optimal exploitation policy as a feedback control rule by applying the Hamilton-Jacobi-Bellman approach and analyze the effects of stochasticity on the optimal policy. Then, we characterize the long-term sustainable optimal state and estimate the risk of stock collapse due to stochastically induced critical depensation. We find that the optimal harvest policy in the stochastic setting is conservative at low stochasticity and approaches the myopic solution at high stochasticity. The risk of stock collapse is increasing with the stochasticity and decreasing with stock sizes.

The Rise and Fall of the Great Fish Pact Under Endogenous Risk of Stock Collapse

Risk of stock collapse is a genuine motivation for cooperative fisheries management. We analyse the effect of an endogenously determined risk of stock collapse on the incentives to cooperate in a Great Fish War model. We establish that equilibrium harvest strategies are non-linear in stock and find that Grand Coalitions can be stable for any number of players if free-riding results in a total depletion of the fish stock. The results thus show conditions under which a Great Fish War becomes a Great Fish Pact. However, this conclusion no longer holds upon dropping the standard assumption that payoffs are evaluated in steady states. If payoffs in the transition between steady states are included, the increased incentives to deviate offset the increased benefits from cooperation due to the presence of endogenous risk and the Great Fish Pact returns to being a Great Fish War.

Genetic analyses reveal declining trends and low effective population size in an overfished South African sciaenid species, the dusky kob (Argyrosomus japonicus)

Overfishing has led to the collapse of many marine fish stocks along the South African coast, particularly species characterised by predictable distribution patterns and vulnerable life-history traits. Dusky kob (Argyrosomus japonicus) is an estuarine-dependent sciaenid fish that has been severely depleted by overfishing and is currently managed by suboptimal management measures aggravated by poor enforcement and compliance to regulations. The present study utilised microsatellite markers to evaluate levels of genetic diversity and population structuring of dusky kob along the South African coast, including five estuarine areas. Results showed signatures of bottlenecking, low and declining trends of effective population size and weak differentiation among samples collected along 2000km of coastline, indicating that dusky kob continues to be subject to the detrimental influence of fishing pressure. Additionally, because dusky kob is a key species in the emerging South African aquaculture sector, parentage analyses were used to successfully identify the origin of first-generation (F1) individuals from a commercial hatchery, hence allowing traceability of farmed products and discrimination between wild and farmed fish. Findings from the present study provided essential information to aid future management of wild populations, as well as to establish sustainable fish farming.

‘All in’: Snow crab, capitalization, and the future of small-scale fisheries in Newfoundland

The collapse of cod stocks off the coast of Newfoundland and Labrador in the early 1990s has been widely identified as one of the greatest human-ecological catastrophes of the 20th century. In the aftermath of the crisis, heated debates took place about how the fishery should be structured in the future in order to facilitate the recovery of stocks and sustain coastal livelihoods. In the end, the trade union representing fishers and fish processing plant workers in the province proved successful in resisting pressures from fish processing companies to introduce full-scale privatization. It was also able to expand access to the lucrative snow crab fishery, thereby improving incomes for most remaining independent fishers in the province. Nevertheless, this paper argues that policy changes made shortly after cod moratorium, in combination with changing environmental, demographic, and market conditions, have created a situation which now threatens to undermine the capacity for small-scale fishing enterprises to remain independently owned and operated into the future.

The Norwegian Winter Herring Fishery: A Story of Technological Progress and Stock Collapse

In the 1970s, herring stocks in the Northeast Atlantic were nearly fished to extinction. This collapse is usually attributed to technological advances. We investigate the empirical impact of technological shocks on herring stocks. We show evidence that the power block was the principal factor in the demise of the stock. We also look at the sensitivity of catch to stock size and technological shocks. We measure a significant stock effect in the 1950s, contrary to what we expect. A simulation model indicates that this could have been caused by an increasing range of the fishing fleet due to ongoing technological progress. (JEL C53, Q22)

Iron fertilisation by Asian dust influences North Pacific sardine regime shifts

Forcing factors and mechanisms underlying multidecadal variability in the production of the world’s major fish stocks are one of the great mysteries of the oceans. The Japanese and California sardine are species that exhibit the regime shifts. It is shown in the present work that during two periods of frequent Asian dust events over the last 100years, sardines on opposite sides of the Pacific Ocean only flourished under a dust-active regime. The earlier such regime that peaked in the 1930s was strong, and it brought synchronous changes in the two species that were linked to the frequency of Asian dust events. However, there is an apparent mismatch in the rise and fall of abundance between the two species in the current dust-active regime. The massive increase in Japanese sardine stock in the 1970s was related to high levels of ocean precipitation and strong winter mixing, whereas the stock collapse since 1988 has been attributed to diminished winter mixing. High levels of ocean precipitation in the western North Pacific effectively cause wet deposition of Asian dust and enhance Japanese sardine stock, whereas it reduces dust flux that can be transported to the eastern North Pacific, delaying the increase of California sardine stock. Analysis further indicates that productivity of Japanese sardine stock is jointly controlled by wet deposition of Asian dust and winter mixing, which supplies macronutrients from depth. California sardine productivity is inversely related to precipitation in the western North Pacific and is positively affected by precipitation off western North America. This indicates that Asian dust influx dominates productivity of the species because of iron-limited ocean productivity in the California sardine ranges. The analysis suggests that dust regime shifts influence shifts in sardine productivity regimes and that iron input from Asian dust during trans-Pacific transport is directly responsible. It appears that in addition to enhancing phytoplankton growth and carbon sinks, atmospheric iron deposition can regulate the production of living ocean resources, which is an extension of Martin’s iron hypothesis.

A Review of Genetic Engineering in Current Aquaculture Practises

Fish represent the main food protein eaten worldwide. Farming of fish has been a traditional practice in South East Asia for over 500 years [1], but with the recent collapse of major fish stocks around the globe and the increasing demand for fish, farming of fish species has turned into an intensive practice that is raising important concerns about its sustainability. With recent advances in genetics and marine biotechnology, aquaculture may undergo a further transformation with the addition of genetically modified organisms (GMOs) to farmed stocks. Genetic engineering of fish and shellfish has been under development for decades but until recently this has been restricted to research experiments [2]. However, after 20 years of pressures from aquaculture and biotechnology companies, the US Food and Drug Administration (FDA) is on the verge of approving genetically modified salmon in US markets [3]. This has opened major debates about the potential environmental outcomes and the possibility of approval by the global market. This article discusses the development of aquaculture over recent years with the advance of genetic engineering using salmon, ‘the king of fish’, as a case study.

From unjust uneconomic growth to sustainable fisheries in Newfoundland: The true costs of closing the inshore fishery for groundfish

Neoliberal economic and social policies during the last 65 years have placed a premium on continuous economic growth. Concern among ecological economists and other critics that economic growth results in loss of natural capital and ecosystem services led to introduction of the concept of “uneconomic growth,” defined as “growth of the macro economy that costs us more than it is worth” (Daly and Farley, Ecological economics principles and applications. Washington: Island Press; 2004). This paper proposes the concept of “unjust uneconomic growth” to pinpoint the additional costs of policies that promote uneconomic growth to the neglect of other considerations and uses the case of Newfoundland and Labrador fisheries policies since 1992 to document it. Newfoundland and Labrador fisheries experienced uneconomic growth in the 1980s leading to the collapse of ground fish stocks. The policies enacted since 1993 based on economic growth goals have failed to solve the ecological-social crisis and entailed additional costs to small-scale fisheries.

Assessing social--ecological trade-offs to advance ecosystem-based fisheries management.

Modern resource management faces trade-offs in the provision of various ecosystem goods and services to humanity. For fisheries management to develop into an ecosystem-based approach, the goal is not only to maximize economic profits, but to consider equally important conservation and social equity goals. We introduce such a triple-bottom line approach to the management of multi-species fisheries using the Baltic Sea as a case study. We apply a coupled ecological-economic optimization model to address the actual fisheries management challenge of trading-off the recovery of collapsed cod stocks versus the health of ecologically important forage fish populations. Management strategies based on profit maximization would rebuild the cod stock to high levels but may cause the risk of stock collapse for forage species with low market value, such as Baltic sprat (Fig. 1A). Economically efficient conservation efforts to protect sprat would be borne almost exclusively by the forage fishery as sprat fishing effort and profits would strongly be reduced. Unless compensation is paid, this would challenge equity between fishing sectors (Fig. 1B). Optimizing equity while respecting sprat biomass precautionary levels would reduce potential profits of the overall Baltic fishery, but may offer an acceptable balance between overall profits, species conservation and social equity (Fig. 1C). Our case study shows a practical example of how an ecosystem-based fisheries management will be able to offer society options to solve common conflicts between different resource uses. Adding equity considerations to the traditional trade-off between economy and ecology will greatly enhance credibility and hence compliance to management decisions, a further footstep towards healthy fish stocks and sustainable fisheries in the world ocean.

Targeting Multiple Management Objectives in Sustainable Fisheries

Modern fisheries management must balance between return (economic value) and risk (harvest uncertainty and stock collapse). Management tools should target multiple simultaneous management objectives. These include output, number of seasons, total stock value and its uncertain fluctuations. I provide a stylized fishery model for simulating the outcomes of these competing management objectives under various regulatory and market environments. Results show that these objectives need not be mutually exclusive. They can be traded off gradually, quantitatively and transparently. The trade-offs involve profit and output versus job provision, employment security, stock conservation and less-risky harvesting. The pursuit of higher return must balance against the risk of stock collapse and harvest fluctuations.

Pollution, habitat loss, fishing, and climate change as critical threats to penguins.

Cumulative human impacts across the world's oceans are considerable. We therefore examined a single model taxonomic group, the penguins (Spheniscidae), to explore how marine species and communities might be at risk of decline or extinction in the southern hemisphere. We sought to determine the most important threats to penguins and to suggest means to mitigate these threats. Our review has relevance to other taxonomic groups in the southern hemisphere and in northern latitudes, where human impacts are greater. Our review was based on an expert assessment and literature review of all 18 penguin species; 49 scientists contributed to the process. For each penguin species, we considered their range and distribution, population trends, and main anthropogenic threats over the past approximately 250 years. These threats were harvesting adults for oil, skin, and feathers and as bait for crab and rock lobster fisheries; harvesting of eggs; terrestrial habitat degradation; marine pollution; fisheries bycatch and resource competition; environmental variability and climate change; and toxic algal poisoning and disease. Habitat loss, pollution, and fishing, all factors humans can readily mitigate, remain the primary threats for penguin species. Their future resilience to further climate change impacts will almost certainly depend on addressing current threats to existing habitat degradation on land and at sea. We suggest protection of breeding habitat, linked to the designation of appropriately scaled marine reserves, including in the High Seas, will be critical for the future conservation of penguins. However, large-scale conservation zones are not always practical or politically feasible and other ecosystem-based management methods that include spatial zoning, bycatch mitigation, and robust harvest control must be developed to maintain marine biodiversity and ensure that ecosystem functioning is maintained across a variety of scales.

A Cod Forsaken Place?: Fishing in an Altered State in Newfoundland

The collapse of cod stocks in the waters off Newfoundland in the early 1990s was widely understood as an ecological disaster and the death of a rural way of life that had endured for centuries. While many areas have remained closed to commercial cod fishing for two full decades, growing numbers of commercial fishers and some fisheries scientists now agree that stocks in several areas are finally showing signs of rebuilding. While the biological recovery of cod populations was once widely viewed as being essential to the future well-being of coastal communities, many commercial fishers now publicly express concerns about the possibility of this scenario actually coming to pass. This article explores the roots of these changing constructions of cod. I argue that making sense of the anxieties and uncertainties that presently surround the question of cod recovery requires paying close attention to the ways in which access to fishery resources has been transformed over time, as well as to the ways in which changing production chains for seafood products, shifting scientific paradigms and practices, and unexpected changes in the marine environment have converged in ways that are fundamentally challenging many previously held notions of the ecological good.

White-beaked dolphin distribution and association with prey in the Barents Sea

In the Barents Sea, strong top predator responses to repeated stock collapses of the forage fish capelin Mallotus villosus have been observed. The white-beaked dolphin Lagenorhynchus albirostris, a flexible predator with a diverse diet in other marine systems, has been associated with capelin in the Barents Sea. Yet, their distribution and foraging ecology in this ecosystem remain largely unknown. Here we use synoptically collected dolphin and prey spatial data to investigate the dolphins' distribution and spatial associations with potential prey species, including the spatial responses to a capelin stock collapse of 2003–2006 and recovery in 2007–2009. Since dolphin–prey associations may be scale-dependent, analyses were conducted at two spatial scales: (1) the habitat scale, by investigating spatial associations between species distributions averaged across years, and (2) the mesoscale, by investigating spatial associations within 50 × 50 km grid cells. At the habitat scale, dolphins overlapped with different prey species in different parts of their habitat. At the mesoscale, the dolphins were associated with blue whiting in southern Atlantic waters, while no prey associations were identified in the Polar Front area, where both capelin and gadoids are abundant. The poor dolphin–prey associations in this area could indicate dolphin distributions spatially constrained by physiological limitations, habitat productivity, or niche partitioning. No strong dolphin responses to capelin collapse and recovery were observed, indicating sufficient availability of alternative prey during the collapse.

Collapse of zooplankton stocks during Liriope tetraphylla (Hydromedusa) blooms and dense mucilaginous aggregations in a thermohaline stratified basin

AbstractA growing number of studies report an increase in jellyfish populations worldwide that may have consequences for marine planktonic food web dynamics. The principal objective of this study was to understand the changes in a zooplankton community during blooms of Liriope tetraphylla and subsequent mucilage events in the Sea of Marmara, a small highly stratified transitional basin between the Black and Aegean Seas. Liriope blooms observed in 2006 and 2007 reached a maximum abundance of 2978 ind.·m−3, following the species' first observation in 2005. Jellyfish species are known to play a key guild role by restructuring plankton communities and in the Sea of Marmara Liriope caused a temporal regime shift from a crustacean‐ to a jellyfish‐controlled system. A rapid decline in abundance of most important zooplankton species followed the Liriope increase, together with a drastic shift in community structure. The dominant summer–autumn species Penilia avirostris (Cladocera) vanished in the autumn of 2006 and was diminished ~30‐fold in 2007 when compared with years without Liriope. The decline in zooplankton and the devastating effects of mucilage on pelagic ecosystem and socio‐economics through restricting commercial fisheries implied sensitivity of the already perturbed Marmara ecosystem to changes in predator densities and environmental stability.

Ecology and conservation of freshwater fish: time to act for a more effective management

Freshwater habitats may account for less than 0.01%of the Earth’s total surface but they play an importantrole in fundamental ecosystem functions and services,besides sustaining an overwhelming diversity of spe-cies (V€or €osmarty et al. 2010; Carpenter et al. 2011).Based on current assessments and projections, theremay be between 25,000 and 40,000 species of fish inthe world, including at least 14,000 freshwater spe-cies (Kottelat & Freyhof 2007), and some 300 newspecies of fish being described every year currently.Every continent has its own distinctive fish faunawhose distribution patterns are the result from physi-cal barriers disrupting past dispersal pathways, aswell as physiological and behavioral adaptations tocope with environmental and habitat-specific charac-teristics (Lucas & Baras 2001; Helfman et al. 2009).This situation imposes different evolutionary pro-cesses resulting in a high genetic differentiationresponsible for a high number of local endemism.Although freshwater fish exhibit great diversityand are responsible for several important functions,their specific roles are still poorly understood.Besides being valuable resources for food, sport andhaving high ornamental value, they are responsiblefor fundamental ecological processes and functionssuch as nutrient cycling, trophic dynamics, productiv-ity, ecosystem engineering and ecosystems connec-tion through migrations, among others. Regrettably,major threats to fish diversity are numerous and mayinteract with each other, thus further complicating thesituation (Dudgeon et al. 2006). Examples of identi-fied threats, to name a few, are overexploitation andflow modification, habitat loss and fragmentation,deleterious effects of agriculture, introduction of non-native species, climate change and pollution includ-ing eutrophication (Dudgeon et al. 2006).Overexploitation of freshwater ecosystems receivesmuch less attention than marine ecosystems althoughthe consequences could be similar if not worse (Allanet al. 2005). Illegal fishing using, for example, pesti-cides, electrofishing and dynamite are responsible forthe collapse of fish stocks and destruction or altera-tion of important freshwater habitats all over theworld.Habitat loss, degradation and fragmentation infreshwater ecosystems are a consequence of altera-tions in land use, such as conversion to agriculture,construction on margins, diversion and abstraction ofwater for human use and human intervention on theriverbed [i.e., channelisation, dredging activities orinaccessibility caused by physical barriers (e.g.,dams)]. Such situations may disrupt migration to suit-able areas for reproduction – especially for migratoryfish, or feeding. In addition, impoundments affectboth longitudinal and lateral connectivity, altering thenatural hydrologic regimes and thus affecting the fishcommunity negatively.Species have been translocated or introduced intonew systems throughout the world for different pur-poses (e.g., stocking for aquaculture and fisheries,sport fishing, release of aquarium species, environ-mental management or frivolously – out of fun, forinstance). During recent years, the number of non-native species introduced to freshwater ecosystemshas increased considerably. Non-native species mayimpact aquatic ecosystems at the individual (e.g.,altering the behaviour of native species, influencinghabitat use and foraging, hybridisation), population(e.g., changing abundance, biomass and distributionof other species), community (e.g., altering interac-tions among populations and potentially inducingtrophic cascades) and ecosystem (e.g., changing

An indicator-based evaluation of Black Sea food web dynamics during 1960–2000

Four Ecopath mass-balance models were implemented for evaluating the structure and function of the Black Sea ecosystem using several ecological indicators during four distinctive periods (1960s, 1980–1987, 1988–1994 and 1995–2000). The results exemplify how the Black Sea ecosystem structure started to change after the 1960s as a result of a series of trophic transformations, i.e., shifts in the energy flow pathways through the food web. These transformations were initiated by anthropogenic factors, such as eutrophication and overfishing, that led to the transfer of large quantities of energy to the trophic dead-end species, which had no natural predators in the ecosystem, i.e., jellyfish whose biomass increased from 0.03gCm−2 in 1960–1969 to 0.933gCm−2 in 1988–1994. Concurrently, an alternative short pathway for energy transfer was formed that converted significant amounts of system production back to detritus. This decreased the transfer efficiency of energy flow from the primary producers to the higher trophic levels from 9% in the 1960s to 3% between 1980 and 1987. We conclude that the anchovy stock collapse and successful establishment of the alien comb-jelly Mnemiopsis in 1989 were rooted in the trophic interactions in the food web, all of which were exacerbated because of the long-term establishment of a combination of anthropogenic stressors.

New methods for impact assessment of biotic-resource depletion in life cycle assessment of fisheries: theory and application

It is difficult to address all of the direct environmental impacts of fisheries using conventional methods of Life Cycle Assessment (LCA). A methodological framework was developed that calculates regionalised characterisation factors for biomass uptake by fishing activities to assess impacts of biotic-resource depletion at both species and ecosystem levels. These two levels were studied to include effects of catch on the collapse of a particular stock of a given species and on total biomass availability in oceans. Characterisation factors were calculated for 127 fish species and 88 marine provinces. The compatibility of this method with other frameworks is discussed, as well as the methodological limitations. The method was applied to two contrasting examples from fisheries (Northern Atlantic albacore tuna and Northern Argentine anchovy). The impacts of one tonne of tuna on biotic natural resources were 4 and 14 times as high as those of anchovy at the ecosystem and species levels, respectively. The application demonstrates that the method is relevant, as it addresses a topic of global interest and fills a gap in LCA impact assessment to contrast impacts of removals of different fish species in terms of biotic natural resource depletion.

Trophic niche partitioning among sympatric baleen whale species following the collapse of groundfish stocks in the Northwest Atlantic

Ecologically similar species may coexist when resource partitioning over time and space reduces interspecific competition. Understanding resource use within these species assem- blages may help predict how species relative abundance might influence ecosystem functioning. In the Gulf of St. Lawrence, Canada, 4 species of rorqual whales (blue Balaenoptera musculus, fin B. physalus, minke B. acutorostrata and humpback Megaptera novaeangliae) coexist during the summer feeding period. They can be observed within hundreds of meters of one another, suggest- ing an overlap in ecological niches; yet fine-scale habitat use analyses suggest some resource par- titioning. While major ecological changes have been observed in marine ecosystems, including the Gulf of St. Lawrence, we have little understanding of how the removal of predatory fish might cascade through ecosystems. Here, we take advantage of a 19 yr tissue collection subsequent to a fishery collapse (which occurred in 1992) to investigate trophic niche partitioning within a guild of rorqual whales following the loss of a key ecosystem component, groundfish. We analyzed stable isotope ratios for 626 rorqual individuals sampled between 1992 and 2010. Using Bayesian iso- topic mixing models, we demonstrated that the 4 rorqual species segregated trophically by consuming different proportions of shared prey. An overall increase in δ 15 N values over the study period (post groundfish collapse), particularly for fin and humpback whales, suggested a progres- sive use of higher-trophic level prey, such as small pelagic fish, whereas the stability of blue whale diet over time confirmed their specialized feeding behaviour. This study provides the first long- term assessment of trophic ecology among rorqual populations on this Northwest Atlantic feeding ground, and evidence for differential resource use among large marine predators following ecosystem change.

Habitat Characteristics Predicting Distribution and Abundance Patterns of Scallops in D’Entrecasteaux Channel, Tasmania

Habitat characteristics greatly influence the patterns of distribution and abundance in scallops, providing structure for the settlement of spat and influencing predation risk and rates of survival. Establishing scallop-habitat relationships is relevant to understanding the ecological processes that regulate scallop populations and to managing critical habitats. This information is particularly relevant for the D’Entrecasteaux Channel, south-eastern Tasmania (147.335 W, 43.220 S), a region that has supported significant but highly variable scallop production over many years, including protracted periods of stock collapse. Three species of scallops are present in the region; the commercial scallop Pecten fumatus, the queen scallop Equichlamys bifrons, and the doughboy scallop Mimachlamys asperrima. We used dive surveys and Generalized Additive Modelling to examine the relationship between the distribution and abundance patterns of each species and associated habitat characteristics. The aggregated distribution of each species could be predicted as a function of sediment type and species-specific habitat structural components. While P. fumatus was strongly associated with finer sediments and E. bifrons with coarse grain sediments, M. asperrima had a less selective association, possibly related to its ability to attach on a wide range of substrates. Other habitat characteristics explaining P. fumatus abundance were depth, Asterias amurensis abundance, shell and macroalgae cover. Equichlamys bifrons was strongly associated with macroalgae and seagrass cover, whereas M. asperrima abundance was greatly explained by sponge cover. The models define a set of relationships from which plausible hypotheses can be developed. We propose that these relationships are mediated by predation pressure as well as the specific behavioural characteristics of each species. The findings also highlight the specific habitat characteristics that are relevant for spatial management and habitat restoration plans.