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Fish Stocks (fish + stock)
Selected AbstractsLocal Influence Diagnostics for Quasi-Likelihood and Lognormal Estimates of a Biological Reference Point from Some Fish Stock and Recruitment ModelsBIOMETRICS, Issue 3 2006N. G. Cadigan Summary We present local influence diagnostics to measure the sensitivity of a biological limit reference point (LRP) estimated from fitting a model to stock and recruitment data. LRPs are low levels of stock size that the management of commercial fisheries should avoid with high probability. The LRP we examine is the stock size at which recruitment is 50% of the maximum (S50%). We derive analytic equations to describe the effects on S50% of changing the weight that observations are given in estimation. We derive equations for the Ricker, Beverton,Holt, and hockey-stick stock-recruit models, and four estimation methods including the error sums of squares method on log responses and three quasi-likelihood methods. We conclude from case studies that the hockey-stick model produces the most robust estimates. [source] Conservation goals and fisheries management units for Atlantic salmon in the Baltic Sea areaJOURNAL OF FISH BIOLOGY, Issue 2001M-L. Koljonen The effective application of genetic information in fisheries management strategies implies political goal setting taking both conservation and fisheries management into account. The concept of sustainable use as set out by the Convention on Biological Diversity offers a valuable starting point in this respect, since the criterion for it is defined as the maintenance of genetic diversity within each species. However, strategic decisions are also needed on the practical level, where the actual genetic information can be taken into account. Genetic factors, such as glacial differentiation, the postglacial genetic structure of populations, gene flow levels and the probability of the existence of adaptive differences, have an effect on the formation of conservation and management units and on the long-term strategy for the sustainable use of aspecies. The Atlantic salmon (Salmo salar) in the Baltic Sea area is treated here as an example of a complicated management problem with a highly hierarchical genetic structure associated with marked loss of naturally reproductive stocks, extensive hatchery production and an effective international offshore fishery. The implications of genetic factors for the conservation and management strategy of the Baltic salmon is discussed in the light of the goals set by the Convention on Biological Diversity, the Straddling Fish Stocks and Highly Migratory Fish Stocks Agreement, the Habitats Directive of the European Union and the International Baltic Sea Fishery Commission. [source] Canadian Foreign Policy and Straddling Stocks; Sustainability in an Interdependent WorldPOLICY STUDIES JOURNAL, Issue 1 2000Alexander Thompson Canada cannot manage Straddling fish Stocks, which extend beyond Canadian waters into the high seas, without an effective foreign fisheriespolicy. This article examines the politics andfate of two such Stocks in the Northwest Atlantic; cod and Greenland halibut. More successful management of Straddling Stocks, I argue, can be achieved if enforcement policies eure conducted within theframework of multilateral ftsheries organizations. By appealing to the rules and Information provided by these Institutions, Canadian governments canpursue more aggressive and proactive fisheries policies while maintaining a high level ofpolitical support at hörne and abroad. [source] Fishery-induced demographic changes in the timing of spawning: consequences for reproductive success,FISH AND FISHERIES, Issue 3 2009Peter J. Wright Abstract Demography can have a significant effect on reproductive timing and the magnitude of such an effect can be comparable to environmentally induced variability. This effect arises because the individuals of many fish species spawn progressively earlier within a season and may produce more egg batches over a longer period as they get older, thus extending their lifetime spawning duration. Inter-annual variation in spawning time is a critical factor in reproductive success because it affects the early environmental conditions experienced by progeny and the period they have to complete phases of development. By reducing the average lifetime spawning duration within a fish stock, fishing pressure could be increasing the variability in reproductive success and reducing long-term stock reproductive potential. Empirical estimates of selection on birth date, from experiments and using otolith microstructure, demonstrate that there is considerable variation in selection on birth date both within a spawning season and between years. The few multi-year studies that have linked egg production with the survival of progeny to the juvenile stage further highlight the uncertainty that adults face in timing their spawning to optimize offspring survival. The production of many small batches of eggs over a long period of time within a season and over a lifetime is therefore likely to decrease variance and increase mean progeny survival. Quantifying this effect of demography on variability in survival requires a focus on lifetime reproductive success rather than year specific relationships between recruitment and stock reproductive potential. Modelling approaches are suggested that can better quantify the likely impact of changing spawning times on year-class strength and lifetime reproductive potential. The evidence presented strengthens the need to avoid fishing severely age truncated fish stocks. [source] The relationship between fishing methods, fisheries management and the estimation of maximum sustainable yieldFISH AND FISHERIES, Issue 4 2002Mark N Maunder Abstract The allocation of effort among fishing gears is as important as controlling effort with respect to both sustainable yield and ecosystem management. Differences in age-specific vulnerability to the fishing method can modify the maximum sustainable yield (MSY) that is obtainable from a fish stock. Different gears or methods are more or less selective for the species targeted, and MSY is rarely, if ever, attainable simultaneously for all species. The different fishing methods capture different types of nontarget species. Some methods will often be more profitable than others, and different user groups will prefer different methods. In many fisheries, it is unlikely that fishing can be limited to a single gear or method, so compromises among them will be required. Global MSY is discussed as a possible reference point for fisheries management. The yellowfin tuna fishery in the eastern Pacific Ocean (EPO) shows all the above characteristics and is used to illustrate effort allocation among fishing methods. [source] Variation in abundance of Norwegian spring-spawning herring (Clupea harengus, Clupeidae) throughout the 20th century and the influence of climatic fluctuationsFISH AND FISHERIES, Issue 3 2000R. Toresen A long-term (1907,98) virtual population analysis (VPA) was made for Norwegian spring-spawning herring (NSSH), which is a huge pelagic fish stock in the north-east Atlantic. It shows that this herring stock has had large fluctuations during the last century; these fluctuations have mainly been determined by variations in the temperature of the inflowing water masses to the region. The spawning stock biomass (SSB) increased from a rather low level in the early years of this century and reached a high level of around 14 million tons by 1930. The spawning stock biomass then decreased to a level of around 10 million tons by 1940, but increased again to a record high level of 16 million tons by 1945. The stock then started to decrease and during the next 20-year period fell to a level of less than 50 000 tons by the late 1960s. Through the 1970s and 1980s, the stock slowly recovered and after the recruitment of strong year classes in 1983 and 1990,1992 the stock recovered to a spawning stock biomass of about 10 million tons. The long-term fluctuation in spawning stock biomass is caused by variations in the survival of recruits. It is found that the long-term changes in spawning stock abundance are highly correlated with the long-term variations in the mean annual temperature of the inflowing Atlantic water masses (through the Kola section) into the north-east Atlantic region. The recruitment is positively correlated with the average temperature in the Kola section in the winter months, January,April, which indicates that environmental factors govern the large-scale fluctuations in production for this herring stock. [source] Seasonal variation in rod recapture rates indicates differential exploitation of Atlantic salmon, Salmo salar, stock componentsFISHERIES MANAGEMENT & ECOLOGY, Issue 3 2007J. L. THORLEY Abstract, Differential exploitation of the various components of a fish stock can adversely affect the diversity, abundance and long-term survival of the entire stock. Many anadromous salmonid stocks exhibit a seasonal structuring of their run-timing that allows fisheries managers to map monthly rod catches onto stock components. To estimate the rod exploitation levels of the various run-timing groups, fishing guides on the River Spey, Scotland, floy-tagged 786 rod-caught and released Atlantic salmon, Salmo salar L., between 2000 and 2002 and recorded recaptures. Whereas 25% of the fish tagged early in March were recaptured, only 2% of those tagged early in June were caught a second time. Exploitation is biased towards the early-running stock components which current assessments show to be least abundant. Management of Atlantic salmon based on an average exploitation rate is inappropriate. [source] The Role of Fish Communities in Water Quality Management of a Large Shallow LakeINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2003István Tátrai Abstract Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the "unplanned" commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2,3 times between 1991,1999, and ranges between 120,194 kg ha,1. Bottom-up effects are more important than the top-down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins. [source] Refilling, ageing and water quality management of Brucher ReservoirLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2002Wilfried Scharf Abstract Refilling of the formerly oligo-mesotrophic, softwater Brucher Reservoir commenced in April 1993 and took 11 months to completely fill. A severe ,trophic upsurge' in the sense of nutrient enrichment (phosphorus, dissolved organic material) as a result of the decomposition of the inundated vegetation occurred. However, algal crop and phosphorus utilization efficiency, expressed as chlorophyll concentrations per unit of total phosphorus, remained very low. In the absence of any fish stock, a single species, Daphnia galeata, monopolized the resources. Sustained by the detritus food chain, daphnids exerted a severe,,top-down' control upon phytoplankton, thereby preventing any net algal growth. In 1994, artificial mixing prevented the occurrence of anoxic water conditions and internal nutrient enrichment of the lake. Although the decay of the inundated vegetation was still of importance, phosphorus concentrations in the water column approached equilibrium with the external input while dissolved organic material concentrations clearly declined. That year, the reservoir became stocked with minnows, sun bleak (Leucaspius delineatus) and trout. As food limitation, as a result of reduced heterotrophic production, became more severe in the face of an increasing predation pressure, the daphnid population density declined, resulting in a decreasing but still adequate community filtering rate providing pronounced ,clear-water phases' of up to 10 m that were features of the period 1995,1997. Although D. galeata defended its key position in the food web, its life-history traits (e.g. body size) changed. Submerged macrophytes, which since 1995 gradually colonized suitable areas of the reservoir, provided a favourable refuge for minnows from trout predation that resulted in reduced predation pressure upon pelagic daphnids. However, in 1998, ungrazeable algae became prominent, adversely affecting transparency. That year, the significant inverse relationship between chlorophyll : total phosphorus ratios and daphnids became uncoupled during the summer (July,August) by indigestible chlorococcalean algae. Nevertheless, the fishery management that was implemented was successful in sustaining not only the lowest yield of algae at the given nutrient concentration but also the most favourable species composition with respect to water quality. [source] CREATION OF MARINE RESERVES AND INCENTIVES FOR BIODIVERSITY CONSERVATIONNATURAL RESOURCE MODELING, Issue 2 2010QUACH THI KHANH NGOC Abstract Despite a number of benefits, marine reserves provide neither incentives for fishermen to protect biodiversity nor compensation for financial loss due to the designation of the reserves. To obtain fishermen's support for marine reserves, some politicians have suggested that managers of new marine reserves should consider subsidizing or compensating those fishermen affected by the new operations. The objective of this paper is to apply principal,agent theory, which is still infrequently applied to fisheries, to define the optimal reserve area, fishing effort, and transfer payments in the context of symmetric and asymmetric information between managers and fishermen. The expected optimal reserve size under asymmetric information is smaller than that under symmetric information. Fishing efforts encouraged with a transfer payment are always less compared to those without payment. This reflects the fact that as the manager induces the fishermen to participate in the conservation program, the fishermen will take into account their effects on fish stock by decreasing their effort. Examples are also supplied to demonstrate these concepts. [source] ENTRY AND EXIT OF LABOR AND CAPITAL IN A FISHERYNATURAL RESOURCE MODELING, Issue 2 2005ASGEIR DANIELSSON ABSTRACT. Exit and entry of fishermen, as well as vessels, is modeled explicitly. If the speed of exit and entry of fishermen is less than instantaneous the wage rate varies with the fortunes of the fishing firms and affects the endogenous labor supply creating a second transmission mechanism from profits to effort. There are realistic cases where this mechanism has important effects on the stability of the dynamic system and on the effects of taxes (subsisdies) on the size of the fish stock. If labor supply depends negatively on the wage rate, the immediate effect of an increase in the tax rate is to increase effort and harvest. This condition makes it also more probable that the dynamic system is unstable. In those cases where the dynamic system is unstable the increase in the tax rate increases overexploitation not only in the short-term but also in the long-term. [source] Herbivorous fishes and the potential of Caribbean marine reserves to preserve coral reef ecosystemsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010Dorothée Kopp Abstract 1.The development of macroalgae to the detriment of corals is now one of the major threats to coral reefs. Herbivorous fishes are partly responsible for algal regulation on coral reefs and their overexploitation favours the shift from scleractinian coral-dominated systems towards macroalgae-dominated systems. 2.Marine protected areas (MPAs) that have been established worldwide may benefit coral reefs through the maintenance of high densities of herbivorous fishes which regulate algal growth. 3.The paper assesses whether small MPAs in the Caribbean are able to enhance herbivorous fish stock and by controlling macroalgae help to maintain reef ecosystems. A visual census using band-transects was undertaken around Guadeloupe island where marine reserves have been in place since 1979. The effects of MPAs on both benthic communities and herbivorous fishes are examined. 4.Inside MPAs, herbivorous fish biomass was almost twice as high as outside MPAs and macroalgal cover was significantly lower. Fish size class distributions revealed that large individuals occurred mainly inside MPAs and that few male individuals were found outside MPAs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Long-term dynamics of pelagic fish density and vendace (Coregonus albula (L.)) stocks in four zones of a lake differing in trawling intensityECOLOGY OF FRESHWATER FISH, Issue 2 2001T. J. Marjomäki Abstract , An 11-year time series of hydroacoustic fish density estimates and fisheries statistics of vendace (Coregonus albula (L.)) from four zones of a lake differing in trawling intensity was analyzed in order to test the hypothesis that intensive trawling has detrimental effects on pelagic fish stocks, especially vendace recruitment. The standardized fish density estimate in trawled zones showed no decrease in comparison to the non-trawled zone. No signs of recruitment failure associable with trawling intensity were found. The growth of vendace at the end of the study period was slower than that at the beginning, indicating a higher density, most clearly so in the zone with highest trawling intensity. No significant correlations were detected between 3-year mean trawling intensity and yield per unit effort of over-1-year-old vendace or fish density in any zone. Thus, no evidence to support the hypothesis was found. This was suggested to be due to density-dependent compensatory processes in recruitment and/or natural mortality effectively counteracting the population change induced by exploitation., [source] An Evaluation of the Cod Fishing Policies of Denmark Iceland and NorwayEUROCHOICES, Issue 3 2004R. Arnason Summary An Evaluation of the Cod Fishing Policies of Denmark, Iceland and Norway Many ocean fisheries are subject to a fundamental economic problem generally referred to as the common property problem. This problem manifests itself as excessive fishing fleets and fishing effort, depressed fish stocks and little or no profitability of the fishing activity, irrespective of the richness of the underlying marine resources. European fisheries represent some of the most dramatic examples of the common property problem. This article employs simple empirical models and recently developed mathematical techniques to examine the economic efficiency of three European fisheries, namely the Danish, Icelandic and Norwegian cod fisheries, The optimal harvesting policies for each of these fisheries are calculated. Comparing these optimal policies with actual harvests provides a measure of the relative efficiency in these three cod fisheries. The comparison confirms the widely held impression that the cod harvesting policies of ail three countries have been hugely inefficient in the past. Moreover, it appears that the inefficiency has been increasing over time. Only during the last few years of our data are there indications that this negative trend may have been halted. Somewhat more surprisingly, in spite of radically different fisheries management systems, we find relatively little difference in the level of stock over-exploitation between these three countries. Politiques compareées de pêhe à la morue au Danemark, en Islande et en Norvège Beaucoup de pêcheries océaniques sont confrontées au problème nique fondamental de la "propriété collective". Celui-ci se manifeste par des flottes de taille excessive, au service d' efforts de péche exagérés, qui aboutissent à détruire les stocks de poisson et la rentabilité des pécheries, en dépit de la richesse des ressources marines sousjacentes. Les pêcheries européennes constituent actuellement l'un des exemples les plus dramatiques des problèmes associés a la propriété collective. On présente ici un modèle empirique assez simple mais associéà de nouvelles techniques mathématiques récemment développé es pour mesurer l' efficacitééconomique de trois types de politiques de pêche à la morue, au Danemark, en Norvège et en Islande. On commence par calculer le volume optimal des prises pour chacun de ces pays. La comparaison entre le niveau optimal et le niveau réel des prises permet de mesurer le degré d' efficacité des politiques suivies. Elle permet de confirmer l'opinion largement répandue selon laquelle les politiques passées ont été extrêmement peu efficaces. En outre, il apparaît que l'inefficacité est croissante avec le temps. C'est seulement dans les toutes dernières années des séries de données que l' on observe un infléchissement de cette tendance négative. Enfin, et c'est le plus surprenant, on trouve peu de differences entre les trois pays en ce qui conceme le degré de surexploitation du stock, et cela, bien que les principes de gestion des pêcheries y soient entiArement différents. Eine Bewertung der Kabeljaufischereipolitik in Dänemark, Island und Norwegen ahlreiche Hochseefischereien tehen einem grundlegenden ftliehen Problem gegenüber, das allgemein als Problem des kollektiven Eigentums bezeichnet wird. Dieses Problem zeigt sich in übermäßig großen Fangflotten und beträchtlichem Fischereiaufwand, geschrumpften Fischbeständen und geringer oder fehlender Rentabilität der Fischerei; dabei ist die Höhe der Fischressourcen unbedeutend für das Problem. Die europäischen Fischereien stellen einige der drastischsten Beispiele für das Problem des kollektiven Eigentums dar. In diesem Beitrag werden einfache empirische Modelle und kürzlich entwickelte mathematische Verfahren angewendet, um die wirtschaftliche Effizienz von drei europäischen Fischereien zu untersuchem der dänischen, der isländischen und der norwegischen Kabeljaufischerei. Für jede dieser Fischereien wird die optimale Nutzungsstrategie berechnet. Aus dem Vergleich dieser optimalen Nutzungsstrategie mit den tatsächlichen Erträgen ergibt sich ein Maß fur die relative Effizienz, die bei diesen drei Kabeljaufischereien vorliegt. Der Vergleich bestätigt den weit verbreiteten Eindruck, dass die Strategien zum Kabeljaufang in alien drei Ländern in der Vergangenheit enorm ineffizient waren. Darüber hinaus wird deutlich, dass die Ineffizienz im Laufe der Zeit zugenommen hat. Lediglich die Daten der letzten jahre enthalten Hinweise darauf, dass dieser negative Trend zum Stillstand gekommen sein könnte. Obwohl sich die Fischwirtschaft in jedem dieser drei Länder sehr stark unterscheidet, lassen sich erstaunlich wenige Unterschiede im Maß der Übernutzung des Fischbestandes finden. [source] The production of n -3 long-chain polyunsaturated fatty acids in transgenic plantsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 11 2006Johnathan A. Napier Abstract Long-chain polyunsaturated fatty acids (LC-PUFA) now have a proven role in human health and nutrition, including the n -3 forms normally found in fish oils. Unfortunately, global fish stocks are now more than ever subject to over-fishing and environmental pollution, indicating the need for an alternative source of fish oils. Recent efforts have focussed on the production of LC-PUFA in transgenic plants to provide a sustainable and clean source of fish oils. The current progress in this area is considered, as well as the bottlenecks that remain to be overcome. [source] SYNTHESIS: Life history change in commercially exploited fish stocks: an analysis of trends across studiesEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 3 2009Diana M. T. Sharpe Abstract Age and size at maturation have declined dramatically in many commercial fish stocks over the past few decades , changes that have been widely attributed to fishing pressure. We performed an analysis of such trends across multiple studies, to test for the consistency of life history changes under fishing, and for their association with the intensity of exploitation (fishing mortality rate). We analyzed 143 time series from 37 commercial fish stocks, the majority of which originated from the North Atlantic. Rates of phenotypic change were calculated for two traditional maturation indices (length and age at 50% maturity), as well as for probabilistic maturation reaction norms (PMRNs). We found that all three indices declined in heavily exploited populations, and at a rate that was strongly correlated with the intensity of fishing (for length at 50% maturity and PMRNs). These results support previous assertions that fishing pressure is playing a major role in the life history changes observed in commercial fish stocks. Rates of change were as strong for PMRNs as for age and size at 50% maturity, which is consistent with the hypothesis that fishing-induced phenotypic changes can sometimes have a genetic basis. [source] ORIGINAL ARTICLE: Implications of fisheries-induced evolution for stock rebuilding and recoveryEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 3 2009Katja Enberg Abstract 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. [source] Genetic population structure of marine fish: mismatch between biological and fisheries management unitsFISH AND FISHERIES, Issue 4 2009Henning Reiss Abstract An essential prerequisite of a sustainable fisheries management is the matching of biologically relevant processes and management action. In fisheries management and assessment, fish stocks are the fundamental biological unit, but the reasoning for the operational management unit is often indistinct and mismatches between the biology and the management action frequently occur. Despite the plethora of population genetic data on marine fishes, to date little or no use is made of the information, despite the fact that the detection of genetic differentiation may indicate reproductively distinct populations. Here, we discuss key aspects of genetic population differentiation in the context of their importance for fisheries management. Furthermore, we evaluate the population structure of all 32 managed marine fish species in the north-east Atlantic and relate this structure to current management units and practice. Although a large number of studies on genetic population structure have been published in the last decades, data are still rare for most exploited species. The mismatch between genetic population structure and the current management units found for six species (Gadus morhua, Melanogrammus aeglefinus, Merlangius merlangus, Micromesistius poutassou, Merluccius merluccius and Clupea harengus), emphasizes the need for a revision of these units and questions the appropriateness of current management measures. The implementation of complex and dynamic population structures into novel and less static management procedures should be a primary task for future fisheries management approaches. [source] Shrinking baseline: the growth in juvenile fisheries, with the Hong Kong grouper fishery as a case studyFISH AND FISHERIES, Issue 4 2009Allen W L To Abstract Historic and current information on the grouper fishery from Hong Kong and adjacent waters reveals significant changes in species composition and fish sizes over the past 50 years in this important Asian centre for seafood consumption. Once dominant, large groupers are now rare and small species and sizes prevail in the present-day fishery. Juveniles comprise over 80% of marketed fish by number among the most commonly retailed groupers, and reproductive-sized fish are absent among larger species. Current fishery practices and the lack of management in Hong Kong and adjacent waters pose a significant threat to large species with limited geographic distribution such as Epinephelus akaara and Epinephelus bruneus, both now listed as threatened by the IUCN. The heavy reliance on juveniles, not only for groupers, but for an increasing diversity of desired fishes within Asia, potentially reduces stock spawning potential. The ,shrinking baseline' in terms of a progressive reduction in fish sizes being marketed in the region can seriously undermine fishery sustainability and recoverability of depleted fish stocks. Fishing pressure on groupers and other valuable food fishes within the Asia-Pacific is intensifying, the declining long-term trend of grouper landings in Hong Kong and the increasing focus on juveniles for immediate sale or for mariculture ,grow-out' signal a worrying direction for regional fisheries. Moreover, the common appearance of small groupers for sale will influence public perception regarding what are ,normal-sized' fish. Management attention is needed if these fisheries are to remain viable. [source] Fishery-induced demographic changes in the timing of spawning: consequences for reproductive success,FISH AND FISHERIES, Issue 3 2009Peter J. Wright Abstract Demography can have a significant effect on reproductive timing and the magnitude of such an effect can be comparable to environmentally induced variability. This effect arises because the individuals of many fish species spawn progressively earlier within a season and may produce more egg batches over a longer period as they get older, thus extending their lifetime spawning duration. Inter-annual variation in spawning time is a critical factor in reproductive success because it affects the early environmental conditions experienced by progeny and the period they have to complete phases of development. By reducing the average lifetime spawning duration within a fish stock, fishing pressure could be increasing the variability in reproductive success and reducing long-term stock reproductive potential. Empirical estimates of selection on birth date, from experiments and using otolith microstructure, demonstrate that there is considerable variation in selection on birth date both within a spawning season and between years. The few multi-year studies that have linked egg production with the survival of progeny to the juvenile stage further highlight the uncertainty that adults face in timing their spawning to optimize offspring survival. The production of many small batches of eggs over a long period of time within a season and over a lifetime is therefore likely to decrease variance and increase mean progeny survival. Quantifying this effect of demography on variability in survival requires a focus on lifetime reproductive success rather than year specific relationships between recruitment and stock reproductive potential. Modelling approaches are suggested that can better quantify the likely impact of changing spawning times on year-class strength and lifetime reproductive potential. The evidence presented strengthens the need to avoid fishing severely age truncated fish stocks. [source] Fishing down the deepFISH AND FISHERIES, Issue 1 2006Telmo Morato Abstract Global landings of demersal marine fishes are demonstrated to have shifted to deeper water species over the last 50 years. Our analysis suggests deep-water fish stocks may be at serious risk of depletion, as their life histories render them highly vulnerable to overfishing with little resilience to over-exploitation. Deep-sea fisheries are exploiting the last refuges for commercial fish species and should not be seen as a replacement for declining resources in shallower waters. Instead, deep-water habitats are new candidates for conservation. [source] The dynamics of collapse in world fisheriesFISH AND FISHERIES, Issue 2 2005Christian Mullon Abstract The fear of a rapid depletion of world fish stocks because of over-exploitation is increasing. Analysis of 1519 main series of the FAO world fisheries catch database over the last 50 years reveals that 366 fisheries' collapses occurred, that is nearly one fishery of four. The robustness of this result is tested by performing several complementary analyses using different conservative options. The number of collapses has been stable through time since 1950s indicating no improvement in the overall fisheries management. Three typical patterns emerge from the analysis of catch series during the period preceding the collapses: smooth collapse (33%), i.e. a long regular decline, erratic collapse (45%), i.e. a fall after several ups and downs, and a plateau-shaped collapse (21%), i.e. a sudden fall after a relatively long and stable persistence of high level of catches. Using a simple mathematical model, we relate the plateau-shaped collapses (which are, by nature, the most difficult to predict) to surreptitiously increasing exploitation and a depensatory mechanism at low population levels. Thus, a stable level of catch over several years is shown to conceal the risk of a sudden collapse. This jeopardizes the common assumption that considers the stability of catch as a goal for fisheries sustainability. [source] Ecological effects of regime shifts in the Bering Sea and eastern North Pacific OceanFISH AND FISHERIES, Issue 2 2002Ashleen J Benson Abstract Large-scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability,from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects. [source] Mesoscale physical processes and the distribution and composition of ichthyoplankton on the southern Brazilian shelf breakFISHERIES OCEANOGRAPHY, Issue 1 2006BÁRBARA CRISTIE FRANCO Abstract The southern Brazilian shelf supports the largest fish stocks in the country, and studies on physical,biological processes in the ecology of ichthyoplankton have been recommended to provide a better understanding of the variability of the recruitment of fishing resources. This study is the first to examine the influence of mesoscale physical processes on the distribution of early life stages of fish in this shelf-break region. Collections of fish eggs and larvae and measurements of temperature and salinity were made at 13 stations along cross-shelf transects in December 1997. Myctophidae, Bregmacerotidae, Clupeidae, Synodontidae and Engraulidae were the most abundant larvae in the northern region, while Engraulidae and Bregmacerotidae prevailed further south. In situ hydrographic data, NOAA/AVHRR images and merged TOPEX/POSEIDON + ERS-1/2 satellite altimetry taken during the cruise revealed an anticyclonic eddy dominating the shelf around 31°S. Larval fish abundance was lower at the centre of this feature, suggesting that the eddy advected poorer offshore waters of tropical origin towards the inner shelf-concentrating the larvae around the eddy. [source] Cladoceran community responses to biomanipulation and re-oligotrophication in Lake Vesijärvi, Finland, as inferred from remains in annually laminated sedimentFRESHWATER BIOLOGY, Issue 6 2010MIRVA NYKÄNEN Summary 1. We studied the role of zooplankton in biomanipulation and the subsequent recovery phase in the Enonselkä basin of Lake Vesijärvi, using subfossil cladocerans in annually laminated sediment. Measures to restore the Enonselkä basin included reduction in external nutrient loading and mass removal of plankti- and benthivorous fish. Water clarity increased and the lake changed from a eutrophic to a mesotrophic state. However, some signs of increased turbidity were observed after 5,10 years of successful recovery. 2. Annual laminae in a freeze core sample were identified and sliced, based on the seasonal succession of diatoms. Cladoceran remains and rotifer eggs were counted, and Daphnia ephippia and Eubosmina and Bosmina ephippia and carapaces were measured. Annual changes in pelagic species composition were studied with principal component analysis. Individual species abundance, size measurements and various cladoceran-based indices or ratios (commonly used to reconstruct changes in trophic state and fish predation) were tested for change between four distinct periods: I (1985,1988) dense fish stocks, poor water quality; II (1989,1992) fish removal; III (1993,1997) low fish density, improved water quality; IV (1998,2002) slightly increased fish density and poorer water quality. 3. After the removal of fish, the mean size of Daphnia ephippia and Eubosmina crassicornis ephippia and carapaces increased significantly. In contrast, the percentage of Daphnia did not increase. When based on ephippia, the ratio Daphnia/(Daphnia + E. crassicornis) increased, but the interpretation was obscured by the tolerance of fish predation by small Daphnia and by the fact that bosminids were the preferred food of roach. Moreover, ephippial production by E. crassicornis decreased in recent years. 4. The abundance of Diaphanosoma brachyurum and Limnosida frontosa increased significantly after the fish population was reduced, while that of Ceriodaphnia and rotifers decreased. 5. The expanding littoral vegetation along with improved water clarity was clearly reflected in the concentration of littoral species in the deep sediment core. The species diversity index for the entire subfossil community also increased. 6. The period of faltering recovery was characterised by greater interannual variability and an increased percentage of rotifers. Nevertheless, the mean sizes of Daphnia ephippia and E. crassicornis ephippia and carapaces indicated a low density of fish. The deteriorating water quality was apparently related to multiple stressors in the catchment after rehabilitation, such as intensified lakeshore building, as well as to exceptional weather conditions, challenging the management methods in use. [source] Review of Swedish regulation and monitoring of aquacultureJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4-5 2000H. Ackefors Summary The aquaculture industry is governed by national Acts, ordinances and regulations. Provisions for the industry have been slightly modified since Sweden entered the EU in 1995. Swedish environmental legislation is applied when potential farmers ask for permission to cultivate. The Acts regulate farming sites, the discharge of water from farms and the species and strains that are permitted to be cultivated. The application procedure for fish farming is comprehensive and judged with regard to the Swedish Acts. Supervision of the aquaculture industry is performed by the County Administrative Board and sometimes also by the Local Administration. All farming units producing stocking material are strictly controlled in an elaborate scheme. Sweden has adopted European Community (EC) directives for shellfish, fish and water quality. Criteria for classifying water quality for concentrations of organic compounds and metals in blue mussels are worked out, and toxins in blue mussels are monitored. EC directives for fresh water quality which aim to sustain fish stocks are adopted as Swedish conditions. [source] A Cue Utilization Approach for Investigating Harvest Decisions in Commons DilemmasJOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 3 2009Donald W. Hine Hierarchical linear modeling (HLM) is introduced as a new tool for investigating decision making in commons dilemmas. University undergraduates (N = 171) managed a virtual fishery, with 2 computer-simulated fishers, over 60 seasons. Level 1 HLM analyses revealed that participants took significantly more fish during seasons when feedback suggested fish stocks, fish value, and fishing expenses were high; and when noncooperative and cooperative others had taken more fish and fewer fish, respectively, in the previous season. Level 2 analyses produced several cross-level interactions, indicating that participants' use of feedback information varied as a function of their social values and environmental attitudes. [source] Spatial and interannual patterns in growth of an exploited coral-reef fishJOURNAL OF FISH BIOLOGY, Issue 4 2007A. J. Williams Patterns of growth in an exploited reef fish Lethrinus miniatus were examined over 5 years (1995,1999) at two spatial scales: (1) among regions of the Great Barrier Reef (GBR) separated by >100 km and (2) among reefs within each of these regions, separated by ,10 km. Mean annual growth of L. miniatus varied significantly among years, but this variation was consistent among ages and regions, indicating that factors that influence temporal patterns in growth were not age-specific and operated at relatively large spatial scales. Significant variation in growth was also observed among some reefs within regions, although the greatest variation was among regions. The average maximum fork length () and average maximum mass (M,) varied significantly among regions, suggesting that productivity of L. miniatus is likely to vary among regions of the GBR. There was also significantly greater mass of fish for a given LF in two regions, which magnified the regional differences in M,. The observed temporal and spatial variation in growth highlighted the importance of a multi-scale approach to population studies and assessment of fish stocks. [source] Distinction between Mulloidichthys flavolineatus juveniles from Reunion Island and Mauritius Island (south-west Indian Ocean) based on otolith morphometricsJOURNAL OF FISH BIOLOGY, Issue 1 2006K. Pothin Sagittal otoliths of the yellowstripe goatfish Mulloidichthys flavolineatus were analysed in order to compare Reunion Island fish stocks with those of Mauritius (south-west Indian Ocean). Conventional otolith morphometric variables (area, perimeter, length and width), shape indices (form factor, roundness, circularity, rectangularity, ellipticity and eccentricity) and Fourier shape analysis were compared between three sites; two in Reunion Island and one in Mauritius. Regional and site-specific differences were found for all the conventional otolith morphometric features. Regarding the shape indices, the differences between sites were best described by form factor, roundness, circularity and rectangularity. A classification by canonical discriminant analysis indicated significant differences between the three sampling sites. The combined use of morphometric variables (size and shape) and external outlines (shape analysis through Fourier series) showed the importance of otolith shape for intraspecific discrimination. [source] Individual-based models of cod movement and population dynamicsJOURNAL OF FISH BIOLOGY, Issue 2003H. J. Edwards Many fish species undergo seasonal changes in distribution, as a result of horizontal migrations between feeding, nursery and spawning grounds. Exploring the processes involved in these movements may be the key to understanding interactions with other species, man and the environment, and is therefore crucial to effective fisheries management. Recent tagging experiments providing information on the distribution of migratory fish stocks have indicated pronounced regional and temporal differences in the migratory behaviour of cod, suggesting complex interactions between this commercially important fish species and the environment. This paper presents a model of the horizontal movements of demersal fish, principally cod, using an individual-based modelling approach to explore and predict the relationship between demersal fish movements and key environmental and ecological factors. The model simulates the basic biological processes of growth, movement and mortality, and is driven by the analysis of physical tagging data recorded by electronic data storage tags (DSTs). Results show that the incorporation of behavioural data from DSTs into spatially explicit individual-based models can provide realistic simulations of large-scale fish stocks, thus giving a better understanding of their basic ecology and allowing more effective management of commercially important fish species. Possibilities of future improvements and extensions to the model are discussed. [source] | ||||||||||||||||||||||