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The Beibu Gulf in China is situated in the tropics, in the western Pacific Ocean. It is an emblematic region combining proximity to a marine biodiversity hotspot and a major seafood hub. Intensification of marine fishing and ocean warming led to a drastic decline in fish populations in the Beibu Gulf during the last decades. This situation urges the development of molecular resources of the Beibu Gulf fish fauna in order to enable automated molecular identifications at the species level for next‐generation monitoring. With this objective, we present the results of a large‐scale campaign to DNA barcode fishes of the Beibu Gulf. We successfully generated 789 new DNA barcodes corresponding to 263 species which, together with 291 sequences mined from Genbank and BOLD, resulted in a reference library of 1080 sequences from 285 species. Based on the use of four DNA‐based species delimitation methods (BIN, ASAP, mPTP, mGMYC), a total of 285 Molecular Operational Taxonomical Units (MOTUs). A single case of cryptic diversity was detected in Scomberomorus guttatus and a single species pair was not captured by delimitation methods. Intraspecific K2P genetic distances averaged 0.36% among sequences within species, whereas K2P genetic distances among species within genera averaged 6.96%. The most speciose families in open water trawling differ from those at fish market, and discrepancies with historical data are discussed in the light of recently documented stock collapses. [ABSTRACT FROM AUTHOR]

Abstract The Beibu Gulf in China is situated in the tropics, in the western Pacific Ocean. It is an emblematic region combining proximity to a marine biodiversity hotspot and a major seafood hub. Intensification of marine fishing and ocean warming led to a drastic decline in fish populations in the Beibu Gulf during the last decades. This situation urges the development of molecular resources of the Beibu Gulf fish fauna in order to enable automated molecular identifications at the species level for next‐generation monitoring. With this objective, we present the results of a large‐scale campaign to DNA barcode fishes of the Beibu Gulf. We successfully generated 789 new DNA barcodes corresponding to 263 species which, together with 291 sequences mined from Genbank and BOLD, resulted in a reference library of 1080 sequences from 285 species. Based on the use of four DNA‐based species delimitation methods (BIN, ASAP, mPTP, mGMYC), a total of 285 Molecular Operational Taxonomical Units (MOTUs). A single case of cryptic diversity was detected in Scomberomorus guttatus and a single species pair was not captured by delimitation methods. Intraspecific K2P genetic distances averaged 0.36% among sequences within species, whereas K2P genetic distances among species within genera averaged 6.96%. The most speciose families in open water trawling differ from those at fish market, and discrepancies with historical data are discussed in the light of recently documented stock collapses.

Stock collapse has profound impacts on ecosystems and fisheries, while the economic impacts have been less studied. The blackspot seabream stock collapsed in the early 1980s and has remain depleted since. The relationship between landings and prices was strongly negative during the decades spanning the collapse (1973–1990) and less during the low stock period with management measures (2003–2020). For other selected species, a significant negative relationship was only found for two species (out of 14) during the earlier period. In contrast, since 2003 prices decreased with landings for most species (10/17) irrespective of their characteristics and their management by a TAC or not. Short-term variations in blackspot seabream prices and landings were also negatively related during the collapse period, indicating rapid market adjustment to decreasing availability. In contrast, in recent years, short-term price variations were not linked to availability change, neither for blackspot seabream nor for most other species (10/17). The study reveals the strong unique effect the blackspot seabream collapse had on price. In the recent period, blackspot became the highest priced fish species in France, making the TAC management essential to limiting catches at sustainable level [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]

ICES assessments of cod (Gadus morhua) in the west of Scotland (ICES Division 6a) suggest the biomass has collapsed and that fishing mortality rate (F) has remained high. In contrast, other stocks in the same fishery, and adjacent cod stocks all show marked declines in fishing mortality and some recovery of the biomass. The perception of the status of 6a cod appears to be dependent on the assumption that the fishery exploitation pattern is flat topped. An assessment that allows the exploitation to take a domed shape produces results that suggest a marked decline in fishing mortality rate and that the spawning stock biomass has recovered to the minimum biomass reference point, Blim. The reduction in F is consistent with substantial reductions in fishing effort and shows a similar pattern to stocks taken within the same fishery. The management implications arising from the two assessments differ substantially. The analysis indicates that benchmark assessments need to test assessment model conditioning assumptions more widely and that management advice needs to consider a more comprehensive range of information about the stock and fishery. [ABSTRACT FROM AUTHOR]

Collapses and regime changes are pervasive in complex systems (such as marine ecosystems) governed by multiple stressors. The demise of Atlantic cod (Gadus morhua) stocks constitutes a text book example of the consequences of overexploiting marine living resources, yet the drivers of these nearly synchronous collapses are still debated. Moreover, it is still unclear why rebuilding of collapsed fish stocks such as cod is often slow or absent. Here, we apply the stochastic cusp model, based on catastrophe theory, and show that collapse and recovery of cod stocks are potentially driven by the specific interaction between exploitation pressure and environmental drivers. Our statistical modelling study demonstrates that for most of the cod stocks, ocean warming could induce a nonlinear discontinuous relationship between fishing pressure and stock size, which would explain hysteresis in their response to reduced exploitation pressure. Our study suggests further that a continuing increase in ocean temperatures will probably limit productivity and hence future fishing opportunities for most cod stocks of the Atlantic Ocean. Moreover, our study contributes to the ongoing discussion on the importance of climate and fishing effects on commercially exploited fish stocks, highlighting the importance of considering discontinuous dynamics in holistic ecosystem-based management approaches, particularly under climate change. [ABSTRACT FROM AUTHOR]

Anchovy (Engraulis encrasicolus, L.) is one of the most important commercial species of the northern and central Adriatic Sea, as well as one of the most productive fisheries in the whole Mediterranean. In the Adriatic Sea the stock of anchovy is shared between Italy, Croatia and Slovenia. A joint stock assessment was carried out using catch data from all the fleets for the time interval 1975-2009. Analyses were performed using estimates of natural mortality at age obtained by means of two different methods and two population dynamics methods based on the analysis of catch-at-age data: Laurec-Sheperd virtual population analysis (VPA) and integrated catch-at-age (ICA), both tuned to acoustic estimates of abundance. Gislason’s estimates for natural mortality appeared to be more realistic and were thus preferred for short-lived species. The general trend of biomass and fishing mortality is similar for the two models, highlighting the major collapse of the stock in 1987. Nevertheless, ICA has enough flexibility to combine all the data available without adding too much complexity in comparison with a VPA approach and seems to perform better in terms of the spawning stock biomass/recruitment relationship and diagnostics (i.e. the retrospective pattern). For the stock status, the exploitation rate from ICA is higher than the suggested threshold of 0.4 proposed by Patterson for small pelagic species.

Several world fish stocks are being explored at unsustainable levels and require management plans to rebuild stock abundance. Defining a management plan is, however, a complex task that entails multidisciplinary work. In fact, while it requires solid scientific knowledge of fish stocks, the inclusion of economic and social objectives is crucial to a successful management implementation. In this paper we develop an age-structured bioeconomic model where the objective function is modified to accommodate preferences from different stakeholders. In particular, we consider important characteristics that a management plan should take into account: profit maximization, fishermen’s preference for reducing landings’ fluctuations and risk of fishery collapse. Modeling preferences for reducing landings’ fluctuations is accomplished by defining a utility function with aversion to intertemporal income fluctuations. Building upon biology literature, we model precautionary concerns by incorporating a probability of collapse that depends on current spawning biomass. We illustrate how this framework is able to assist in the analysis and design of harvest control rules applying it to the Ibero-Atlantic sardine stock. [ABSTRACT FROM AUTHOR]

In the late 1960s, two local herring stocks and one seasonal migratory herring stock in Icelandic waters collapsed primarily due to overfishing. While the stocks of Icelandic summer-spawning herring (ISSH) and Norwegian spring-spawning herring (NSSH) have recovered, Icelandic spring-spawning herring (ISPH) has not. The main objective of this work is to explore the existence of ISPH and identify potential signs of recovery. Analyses were based on samples from the autumn fishery and survey data from 1962 to 2016. In the autumn, local ISSH and ISPH cohabitated and mixed in the main fishery, where sampled fish were categorized into stocks on basis of maturity stage. The results indicate that the proportion of ISPH was in the range of 13–33% in the 1960s while below 5% and on average 1.4% during 1970–2016. Several year classes of ISPH exhibit notable differences from the general low levels and caused a slight increase in ISPH spawning-stock biomass for corresponding years. An increase in proportion of generally old ISPH around 2004 and 2013 occurred simultaneously with the reappearances of NSSH in the feeding areas east and north of Iceland, respectively. Altogether, it supports earlier suggestions that ISPH might require immigration from NSSH to recover, as these were considered closely related stocks. This is consistent with the source-sink theoretical model of stock size regulation. [ABSTRACT FROM AUTHOR]

Globally, overexploitation of fishery stocks is a complex problem aggravated by climate change's effects. The green abalone in Mexico is an overexploited fishery, resulting in stakeholders committing to its recovery. Part of a comprehensive co-management strategy was to implement a fishing closure in some fishing areas. Now they are exploring reopening the fishery and gradually increasing fishing efforts. This research evaluates compatible management strategies with stock rebuilding under climate uncertainty. An age-structured bioeconomic model for the green abalone fishery was parameterized, which considered the impact of SST anomalies on population dynamics (i.e., recruitment, mortality, and growth). Three management strategies were evaluated under future climate scenarios (RCP 4.5, RCP 8.5, and a scenario without climate change). Results indicate that an effort level that aims to generate Maximum Sustainable Yield (MSY) based on historical fishery data may lead to overexploitation under warming scenarios. Instead, applying the minimum acceptable effort for the fishing community can support biomass recovery and is a strategy more resilient to climate change. This finding highlights the risk of overexploitation by assuming stock productivity stability under favorable climatic conditions when designing rebuilding plans. A stock rebuilding strategy will be more likely to succeed if it is cautious, recognizes uncertainties, and is flexible in considering stock productivity changes. [ABSTRACT FROM AUTHOR]

This 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 downwardsloping 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. [ABSTRACT FROM AUTHOR]

Fish stocks around the world are heavily overexploited in spite of fishing policies in several parts of the world designed to limit overfishing. Recent studies have found that the complexity of ecological systems and the diversity of species, as well as negative impact of fishing activities on environmental carrying capacity of fish stocks-all contribute to the problem. A number of biologists, managers, and practitioners strongly support the use of marine reserves as a management strategy for marine conservation. This paper contributes to this line of research by seeking an optimum reserve size and fishing effort for situations where species diversity decrease at fishing grounds and fishing activities impact carrying capacity. We found that a reserve size which maximizes economic rents could ruin a fish stock if fishing impacts are not accounted for. On the other hand, the reserve serves as a bifurcation term which could improve the resilience of a marine ecosystem. [ABSTRACT FROM AUTHOR]

Jansen, T. 2014. Pseudocollapse and rebuilding of North Sea mackerel (Scomber scombrus). – ICES Journal of Marine Science, 71: 299–307.The largest observed change in mackerel (Scomber scombrus) abundance in the North Atlantic happened when the so-called “North Sea mackerel” collapsed due to overfishing. Despite protection, it has remained in a depleted state. Central to this interpretation was that the “North Sea mackerel” was considered to be a distinct spawning component. However, a recent study has shown that this is not likely. In the light of this study, a review of the history of mackerel spawning in the North Sea found that the traditional explanation of the collapse did not account for a range of unfavourable environmental changes: high fishing pressure was followed by decreasing temperatures that reduced the spawning migration into the North Sea. This was further supplemented by unfavourable changes in food and wind-induced turbulence. On the population level, this was, therefore, not a local stock collapse, but a southwest shift in spawning distribution combined with a reduction in that portion of the population cline with an affinity for spawning in the northeastern part of the spawning area, including the North Sea. No indication of irreversible genetic or behavioural losses caused by the events was found. The previously unexplained lack of rebuilding of spawning in the North Sea consequently seems related to two environmental factors that have remained unfavourable: (i) zooplankton concentration, and (ii) wind-induced turbulence. Furthermore, the large commercial autumn–winter fishery in the North Sea continues to land unknown quantities of mackerel that have an affinity for spawning in the northeastern part of the spawning area, including the North Sea. [ABSTRACT FROM PUBLISHER]

We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management. [ABSTRACT FROM AUTHOR]

We develop a bioeconomic model to analyze a fishery with fixed costs as well as a within-season continuous cost function for the generalized Schaefer production function with increasing marginal returns to effort level. We analyze the consequences of the combined effects of increasing marginal returns and fixed costs. We find that regardless of the magnitude of the fixed costs, cyclical policies are optimal. We also demonstrate that the danger of potential collapse increases with increasing fixed costs. This result is quite counterintuitive, as higher costs are usually considered to have a conservative effect on resources. [ABSTRACT FROM AUTHOR]

It is well established in the fisheries management literature that marine ecosystems are complex and marine species depend on one another. As a result, it is important to account for species diversity to ensure sustainable management. In addition, recent research published in the marine sciences literature has provided unequivocal evidence that fishing activities destroy habitats and inhibit production of planktons. This paper illustrates that if a conventional bioeconomic model is employed, an optimum effort policy as opposed to quota appears to result in sustainable management even if fishing impacts carrying capacity. However, the so-called optimum effort may collapse the stock if species diversity is not accounted for. Conversely, if species diversity and the impact of fishing on carrying capacity are considered, neither the equilibrium quota nor effort may guarantee sustainable yield. [Copyright &y& Elsevier]

Mass mortality events are relatively uncommon in commercially fished populations, but when they occur, they reduce production and degrade ecosystems. Observing and documenting mass mortalities is simpler than quantifying the impact on stocks, monitoring or predicting recovery, and re-establishing commercial fishing. Direct survey measures of abundance, distribution and harvestable biomass provide the most tenable approach to informing decisions about future harvests in cases where stock collapses have occurred because conventional methods have been disrupted and are less applicable. Abalone viral ganglioneuritis (AVG) has resulted in high levels of mortality across all length classes of blacklip abalone, Haliotis rubra Leach, off western Victoria, Australia, since May 2006. Commercial catches in this previously valuable fishery were reduced substantially. This paper describes the integration of research surveys with commercial fishermen's knowledge to estimate the biomass of abalone on AVG-impacted reefs. Experienced commercial abalone divers provided credible information on the precise locations of historical fishing grounds within which fishery-independent surveys were undertaken. Abalone density estimates remained low relative to pre-AVG levels, and total biomass estimates were similar to historical annual catch levels, indicating that the abalone populations have yet to adequately recover. Survey biomass estimates were incorporated into harvest decision tables and used with prior accumulated knowledge of the populations to determine a conservative harvest strategy for the fishery. [ABSTRACT FROM AUTHOR]

Bakun, A., Babcock, E. A., and Santora, C. 2009. Regulating a complex adaptive system via its wasp-waist: grappling with ecosystem-based management of the New England herring fishery. – ICES Journal of Marine Science, 66: 1768–1775.We use the New England herring fishery as an example of the unresolved scientific issues pertinent to ecosystem-based management of forage-fish fisheries. The biomass of herring off New England is currently well above maximum sustainable yield (BMSY), leading to pressure for expanded harvests. Associated concerns include: the maintenance of sufficiently abundant forage to meet the current needs of marine mammals and seabirds while supporting the rebuilding of overfished groundfish resources; the preservation of the service functions of a healthy population of pelagic zooplanktivorous fish to prevent possible outbreaks of pests, or hypoxia events; and the limitation of unintended bycatch of marine mammals, seabirds, and juvenile stages of groundfish. Perhaps a self-enhancing feedback loop, involving predation by herring on the early life stages of their groundfish predators, might result in regime shifts that could not be easily reversed. A plausible outcome of these ideas is a dichotomy in management choice between (i) promoting an ecosystem dominated by valuable groundfish resources and (ii) promoting the current ecosystem that features a large herring resource associated with abundant and energy-rich forage for marine mammals, seabirds, and continued high productivity of valuable shellfish resources. [ABSTRACT FROM PUBLISHER]

Marine ecosystems are complex, and many marine species are ecologically interdependent. As a result, losing a species could produce a cascading effect on other species. Fishery scientists advocate an ecosystem-based approach to fishery management to meet long-term sustainable goals. This paper models the complex interrelationships among species and the relationship between biomass growth and phenotypic diversity. We found that the equilibrium stock and catch/yield levels are overestimated when the diversity is not accounted for. Consequently, if species are diverse, fishery policy based on a single fishery management could overestimate catch potentials and potentially results in biological overfishing and stock collapse. [Copyright &y& Elsevier]

Worldwide depletion of fish stocks has led fisheries managers to become increasingly concerned about rebuilding and recovery planning. To succeed, factors affecting recovery dynamics need to be understood, including the role of fisheries-induced evolution. Here we investigate a stock’s response to fishing followed by a harvest moratorium by analyzing an individual-based evolutionary model parameterized for Atlantic cod Gadus morhua from its northern range, representative of long-lived, late-maturing species. The model allows evolution of life-history processes including maturation, reproduction, and growth. It also incorporates environmental variability, phenotypic plasticity, and density-dependent feedbacks. Fisheries-induced evolution affects recovery in several ways. The first decades of recovery were dominated by demographic and density-dependent processes. Biomass rebuilding was only lightly influenced by fisheries-induced evolution, whereas other stock characteristics such as maturation age, spawning stock biomass, and recruitment were substantially affected, recovering to new demographic equilibria below their preharvest levels. This is because genetic traits took thousands of years to evolve back to preharvest levels, indicating that natural selection driving recovery of these traits is weaker than fisheries-induced selection was. Our results strengthen the case for proactive management of fisheries-induced evolution, as the restoration of genetic traits altered by fishing is slow and may even be impractical. [ABSTRACT FROM AUTHOR]

The Barents Sea capelin stock underwent drastic changes in stock size during the last three decades. Three stock collapses occurred in 1985-1989, 1993-1997, and 2003-2006. The collapses had effects both downwards and upwards in the food web. The release in predation pressure from the capelin stock led to increased amounts of zooplankton during the collapse periods. When capelin biomass was drastically reduced, its predators were affected in various ways. Cod experienced increased cannibalism, growth was reduced and maturation delayed. Sea birds experienced increased rates of mortality and total recruitment failures, and breeding colonies were abandoned for several years. Harp seals experienced food shortage, increased mortality because they invaded the coastal areas and were caught in fishing gears, and recruitment failures. There is evidence for differences in how the three capelin collapses affected the predators. The effects were most serious during the 1985-1989 collapse and can hardly be traced during the ongoing collapse. We conclude that these differences likely result from increased availability of alternative food sources during the two last periods of collapse. [ABSTRACT FROM AUTHOR]

Abstract: Many articles have been published in recent years criticizing the management of living marine resources based solely on biological stock conservation criteria. In the United States and in many parts of the rest of the world, multiple management objectives and goals in addition to stock conservation must be met by fishery managers responsible for the marine resources under their control. An alternative management metric, conservation efficiency, is recommended based instead on a multi-disciplinary scientific framework that captures these different goals and the behavior of participants in the fishery. On the basis of the constraints facing managers, resources can be conserved and the quality of life of consumptive and nonconsumptive fishery participants improved. [Copyright &y& Elsevier]

Abstract: On the basis of data from the North Sea herring fishery, we discuss the consequences of increasing marginal returns on the exploitation of renewable resources. We show that high, but still reasonable, discount rates can cause extinction to be optimal even in the ideal case of a sole owner and a resource with a high growth rate. In the case of lower discount rates, optimal cyclical policies can periodically drive the resource to levels approaching Safe Minimum Standards. We discuss the sustainability, intergenerational equity, social risk aversion, and theoretical issues raised by increasing marginal returns. [Copyright &y& Elsevier]

Abstract: Predicting crossings between stable states is a central issue in population biology. Crossings from low-density to high-density equilibria are often associated with pest outbreaks, while the opposite crossings are often associated with population collapse of harvested species. Here I use a simple, bistable model to demonstrate a technique for estimating mean first passage times (MFPT) of thresholds, including boundaries between stable equilibria. The approach is based on stochastic “shot–noise” perturbations to the population and the MFPTs compare favorably with mean crossing times from Monte Carlo numerical solutions of the stochastically perturbed model. This agreement suggests that MFPT approximations can be used to quantify expected effects of species manipulations, whether the goal is pest control or sustainable harvest. [Copyright &y& Elsevier]

The Norwegian spring-spawning herring (Clupea harengus) population collapsed to the state of commercial extinction in the late 1960s; the stock remained at extremely low levels for over two decades, but has recovered fully since the 1980s. It is known that the collapse coincided with strong changes in maturation characteristics. However, the long-term patterns of maturation in this stock have remained largely undescribed. We applied discriminant and neural network analysis to historical scale data to predict age at maturation for individual herring of the year-classes 1930–1992. Based on these data, this paper (1) presents new, revised maturity ogives for these year-classes with a temporal resolution of 1 year and (2) describes the long-term variability in age at 50% maturity, length at 50% maturity, and length-at-age. This new information shows that during the period of low stock abundance, age at 50% maturity was considerably reduced and length at 50% maturity moderately increased as compared to the situation both before and after the collapse. These variations coincided with changes in length-at-age, suggesting that the maturity changes to a large extent reflect variations in body growth related with stock abundance. [Copyright &y& Elsevier]

Assessments of many West African fish stocks rely on fishery dependent catch and effort data. Typically, these treat the catch data as error free and some assume that fishing power does not change over time. To address these issues we develop a fleet based surplus production model that accounts for increases in fishing power. It allows errors both in effort and catch data so avoiding the assumption that catch data are exact. Mean annual fleet fishing power increase can be estimated when data from multiple fleets are available provided it can be specified for at least one fleet. The model is tested using simulated data and then applied to western stocks of anchovy (Engraulis encrasicolus) and bonga shad (Ethmalosa fimbriata) in the Fishery Committee for the Eastern Central Atlantic (CECAF) area. Both stocks appear to be over-exploited and near to collapse. Corrections for fishing power are important in the anchovy assessment and help to explain conflicting trends in the data. Uncertainty in the assessments is explored with a range of sensitivity tests. [ABSTRACT FROM AUTHOR]

The idea of using marine reserves, where all fishing is banned is not new to fisheries management. It was first formally considered by Beverton and Holt but rejected in favour of approaches such as fleet and gear control. Since that analysis, many fisheries have collapsed worldwide, illustrating the vulnerability of fishery resources and the ineffectiveness of these approaches. Empirical data and modelling suggest that marine reserves would generally increase yields, especially at the high fishing mortality that occurs in most fisheries. However, the most interesting feature of reserves is their ability to provide resilience to overexploitation, thereby reducing the risk of stock collapse. Benefits from reserves come from the increase in biomass and individual size within them, resulting in adult migration and/or larval dispersal that would replenish fishing grounds. The use of marine reserves in managing fisheries necessitates a thorough understanding of critical habitat requirements, fish movement, fish behaviour, the relations between subpopulations and the critical density effect for larval dispersal. When properly designed, and coupled with other management practices, reserves may provide a better insurance against uncertainties in stock assessment, fishing control and management by protecting a part of the population from exploitation. This strategy can be used for both sedentary and migratory species. [ABSTRACT FROM AUTHOR]

Fisheries-induced evolution has been hypothesized to delay the recovery of collapsed fish stocks through effects on their productivity. The cod stock in the southern Gulf of St. Lawrence (SGSL) collapsed in the early 1990s and has shown no recovery since then, due mainly to high natural mortality of adult cod. Age and size at maturation of SGSL cod decreased sharply over time in cohorts produced in the 1950s and 1960s, likely reflecting an evolutionary response to intensified fishing, and have remained low since then, despite severe reductions in fishing mortality over the past 15 years. A predicted consequence of early maturation is increased natural mortality due to higher costs to reproduction. Early maturation may be a cause of increases in natural mortality of SGSL cod in the 1970s but does not appear to be related to the much larger increases since then. Instead, the current high natural mortality of SGSL cod appears to be primarily a cause, rather than a consequence, of the continued early maturation in this population, now replacing fishing mortality as the agent of selection favouring early maturity. This striking example of the failure to reverse fisheries-induced evolution by relaxing fishing pressure emphasizes the need for management strategies that minimize the chances of harvest-induced genetic change.