Showing papers on "Fishing published in 2000"

The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems

Abstract: Stevens, J. D., Bonfil, R., Dulvy, N. K., and Walker, P. A. 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. – ICES Journal of Marine Science, 57: 476–494. The impact of fishing on chondrichthyan stocks around the world is currently the focus of considerable international concern. Most chondrichthyan populations are of low productivity relative to teleost fishes, a consequence of their different life-history strategies. This is reflected in the poor record of sustainability of target shark fisheries. Most sharks and some batoids are predators at, or near, the top of marine food webs. The effects of fishing are examined at the single-species level and through trophic interactions. We summarize the status of chondrichthyan fisheries from around the world. Some 50% of the estimated global catch of chondrichthyans is taken as by-catch, does not appear in official fishery statistics, and is almost totally unmanaged. When taken as by-catch, they are often subjected to high fishing mortality directed at teleost target species. Consequently, some skates, sawfish, and deep-water dogfish have been virtually extirpated from large regions. Some chondrichthyans are more resilient to fishing and we examine predictions on the vulnerability of different species based on their life-history and population parameters. At the species level, fishing may alter size structure and population parameters in response to changes in species abundance. We review the evidence for such density-dependent change. Fishing can affect trophic interactions and we examine cases of apparent species replacement and shifts in community composition. Sharks and rays learn to associate trawlers with food and feeding on discards may increase their populations. Using ECOSIM, we make some predictions about the long-term response of ecosystems to fishing on sharks. Three different environments are analysed: a tropical shelf ecosystem in Venezuela, a Hawaiian coral reef ecosystem, and a North Pacific oceanic ecosystem. 2000 International Council for the Exploration of the Sea

Fishing, selection, and phenotypic evolution

Abstract: Large changes are taking place in yield-determining traits of commercially exploited fish, including traits such as size-at-age and age-at-maturation. The cause of these phenotypic changes is often not understood, and genetic change arising from the selective effects of fishing may be a contributory factor. Selection generated by fishing gear is strong in heavily exploited fish stocks, and the spatial location of fishing can also cause strong selection. The success of selective breeding in aquaculture indicates that significant amounts of genetic variation for production-related traits exist in fish populations. Fisheries managers should be alert to the evolutionary change caused by fishing, because such changes are likely to be hard to reverse and, if properly controlled, could bring about an evolutionary gain in yield.

A quantitative analysis of fishing impacts on shelf-sea benthos

Abstract: 1. The effects of towed bottom-fishing gear on benthic communities is the subject of heated debate, but the generality of trawl effects with respect to gear and habitat types is poorly understood. To address this deficiency we undertook a meta-analysis of 39 published fishing impact studies. 2. Our analysis shows that inter-tidal dredging and scallop dredging have the greatest initial effects on benthic biota, while trawling has less effect. Fauna in stable gravel, mud and biogenic habitats are more adversely affected than those in less consolidated coarse sediments. 3. Recovery rate appears most rapid in these less physically stable habitats, which are generally inhabited by more opportunistic species. However, defined areas that are fished in excess of three times per year (as occurs in parts of the North Sea and Georges Bank) are likely to be maintained in a permanently altered state. 4. We conclude that intuition about how fishing ought to affect benthic communities is generally supported, but that there are substantial gaps in the available data, which urgently need to be filled. In particular, data on impacts and recovery of epifaunal structure-forming benthic communities are badly needed.

Large-scale closed areas as a fishery-management tool in temperate marine systems : The Georges Bank experience

Abstract: Seasonal closed areas have been an element of fishery management in New England waters since 1970 but before 1994 had limited impact on the conservation of groundfish stocks for which they were designed. Beginning in December of 1994, three large areas of historic importance to groundfish spawning and juvenile production on Georges Bank and in Southern New England, totaling 17,000 km 2 , were closed year-round to any gears capable of retaining groundfish (trawls, scallop dredges, gill nets, hook fishing). In the ensuing five years, the closed areas contributed significantly to reduced fishing mortality of depleted groundfish stocks. Placements of the closed areas afforded the greatest year-round protection to the shallow-sedentary assemblage of fishes (primarily flounders, skates, and miscellaneous others) and bivalve molluscs. Although the closures afforded less year-round protection to migratory age groups of Atlantic cod, Gadus morhua, and haddock, Melanogrammus aeglefinus, additional new regulations in open areas and in the Canadian portions of Georges Bank also contributed to the observed reductions in stock-wide fishing mortality rates. The areas were closed to dredge gear designed for sea scallops, Placopecten magellanicus, because of groundfish by-catch (particularly of flounders). Scallop biomass increased 14-fold within the closed areas during 1994-1998. In July 1998, total and harvestable scallop biomasses were 9 and 14 times denser, respectively, in closed than in adjacent open areas. A portion of the closed areas was designated a habitat area of particular concern on the basis of patterns of occurrence of juvenile groundfish in gravel/cobble sediment types. Managers reopened portions of one closed area to sea-scallop dredging in 1999, but restrictions on gear and areas fished were used to minimize groundfish by-catch and impact on juvenile cod and haddock on gravel substrates. Results from these reopenings have encouraged managers to contemplate a formal 'area rotation' scheme for scallops intended to improve yield per recruit. Closures of large portions of Georges Bank have proved to be an important element leading to more effective conservation of numerous resource and nonresource species, despite selection of the closed areas on the basis of seasonal spawning grounds of haddock and the distribution of yellowtail flounder, Limanda ferrugineus, in southern New England. In the future, factors other than fishing mortality reduction, including optimal placement to enhance larval production and to protect nursery areas and spawning concentrations, may well influence the selection of closed-area boundaries.

Impacts of climatic change and fishing on Pacific salmon abundance over the past 300 years.

Abstract: The effects of climate variability on Pacific salmon abundance are uncertain because historical records are short and are complicated by commercial harvesting and habitat alteration. We use lake sediment records of δ 15 N and biological indicators to reconstruct sockeye salmon abundance in the Bristol Bay and Kodiak Island regions of Alaska over the past 300 years. Marked shifts in populations occurred over decades during this period, and some pronounced changes appear to be related to climatic change. Variations in salmon returns due to climate or harvesting can have strong impacts on sockeye nursery lake productivity in systems where adult salmon carcasses are important nutrient sources.

The impact of fishing of marine birds

Abstract: Birds are the most conspicuous, wide-ranging, and easily studied organisms in the marine environment. They can be both predators and scavengers, and they can be harmed by and can benefit from fishing activities. The effects of fishing on birds may be direct or indirect. Most direct effects involve killing by fishing gear, although on a lesser scale some fishing activities also disturb birds. Net fisheries and hook fisheries have both had serious negative effects at the population level. Currently, a major negative impact comes from the by-catch of albatrosses and petrels in long-lines in the North Pacific and in the Southern Ocean. High seas drift nets have had, prior to the banning of their use, a considerable impact on seabirds in the northern Pacific, as have gillnets in south-west Greenland, eastern Canada, and elsewhere. Indirect effects mostly work through the alteration in food supplies. Many activities increase the food supply by providing large quantities of discarded fish and wastes, particularly those from large, demersal species that are inaccessible to seabirds, from fishing vessels to scavengers. Also, fishing has changed the structure of marine communities. Fishing activities have led to depletion of some fish species fed upon by seabirds, but may also lead to an increase in small fish prey by reducing numbers of larger fish that may compete with birds. Both direct and indirect effects are likely to have operated at the global population level on some species. Proving the scale of fisheries effects can be difficult because of confounding and interacting combinations with other anthropogenic effects (pollution, hunting, disturbance) and oceanographic factors. Effects of aquaculture have not been included in the review

Tropical Estuarine Fishes: Ecology, Exploitation and Conservation

Abstract: Series Foreword. Preface and Acknowledgements. 1. Scope and Definitions. 2. The Diversity of tropical Estuaries. 3. Fish Faunas and Communities. 4. Trophic Ecology. 5. Reproductive Strategies. 6. Effects of Structure and Hydrology. 7. Mangroves and Estuarine Dependence. 8. Estuarine Fisheries. 9. Effects of Fishing. 10. Effects of Industry and Agriculture. 11. Conservation, Rehabilitation and Climate Change. References. Taxonomic Index. Geographic Index. Subject Index.

The impacts of fishing on marine birds

Abstract: Birds are the most conspicuous, wide-ranging, and easily studied organisms in the marine environment. They can be both predators and scavengers, and they can be harmed by and can benefit from fishing activities. The effects of fishing on birds may be direct or indirect. Most direct effects involve killing by fishing gear, although on a lesser scale some fishing activities also disturb birds. Net fisheries and hook fisheries have both had serious negative effects at the population level. Currently, a major negative impact comes from the by-catch of albatrosses and petrels in long-lines in the North Pacific and in the Southern Ocean. High seas drift nets have had, prior to the banning of their use, a considerable impact on seabirds in the northern Pacific, as have gillnets in south-west Greenland, eastern Canada, and elsewhere. Indirect effects mostly work through the alteration in food supplies. Many activities increase the food supply by providing large quantities of discarded fish and wastes, particularly those from large, demersal species that are inaccessible to seabirds, from fishing vessels to scavengers. Also, fishing has changed the structure of marine communities. Fishing activities have led to depletion of some fish species fed upon by seabirds, but may also lead to an increase in small fish prey by reducing numbers of larger fish that may compete with birds. Both direct and indirect effects are likely to have operated at the global population level on some species. Proving the scale of fisheries effects can be difficult because of confounding and interacting combinations with other anthropogenic effects (pollution, hunting, disturbance) and oceanographic factors. Effects of aquaculture have not been included in the review. 2000 International Council for the Exploration of the Sea

Chronic fishing disturbance has changed shelf sea benthic community structure

Abstract: Summary 1. Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2. In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3. Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state.

Source-sink population dynamics and the problem of siting marine reserves

Abstract: Marine protected areas (MPAs) have been proposed as one way to reduce the problems of overfishing and to respond to uncertainty in fisheries management. Many fisheries, including tropical and temperate reef fisheries, are inherently multispecies, multigear fisheries and are difficult to manage by traditional methods. Clearly, these fisheries should benefit from the establishment of no-take marine reserves, but the track record to date for fisheries benefits of MPAs is mixed or poorly documented. Because siting of reserves depends upon both scientific and sociological input, the lack of critical scientific information on source-sink population structure of reef fishes can potentially lead to MPA placement that can damage rather than enhance fisheries. In this paper, we develop a simple, spatially explicit model to address a series of hypotheses regarding MPA effects on fisheries. Our hypotheses include: (1) a system in which reserves are placed in source habitats is superior to one in which they are placed at random or in sink habitats; (2) the importance of source-sink population structure is increased if fishing effort is displaced rather than reduced; (3) as the proportion of the environment consisting of poor-quality (sink) habitat increases, proper siting of MPAs becomes increasingly important; and (4) if the environment contains directional currents, the spatial location of reserves will be critical to population enhancement. Our results suggest that, if reef fishes have source-sink population dynamics, siting reserves on the basis of sociological criteria alone may be risky. We need to understand source-sink population dynamics to site MPAs properly.

Effects of fishing on the structure and functioning of estuarine and nearshore ecosystems

Abstract: Estuaries and associated coastal waters support many essential fisheries, a fact which contributes to their disproportionately high economic value. They are, however, also among the most extensively modified and threatened of aquatic environments. Almost all have been strongly affected by human beings, and fisheries are an integral part of human activities on the coast. We have taken a global perspective in synthesizing the effects of fishing on estuaries and coastal waters. Rather than attempt to cover all regions of the world in detail, we review eight process-orientated categories affected by fishing, with case studies for each of them: target organisms, non-target organisms, nursery functions, trophic effects, habitat change, reduced water quality, human environment, and potential for local extinctions. Fishing in the estuarine and nearshore environment has clear impacts on the structure and functioning of these ecosystems, although other, non-fishing issues also effect these ecosystems. This creates multiple interactions and reinforces the need for an integrated approach to coastal zone management. Nonetheless, some form of fish-based action plan could be created, especially within estuaries, which would provide management objectives for a particular system.

The effects of fishing on non-target species and habitats: biological, conservation and socio-economic issues

Abstract: Introduction. Acknowledgements. Contributors. PART 1: Distribution of Fishing Effort and Physical Interaction with the Seabed. 1. Spatial and temporal patterns in North Sea fishing effort (S. Jennings, K.J. Warr, S.P.R. Greenstreet and A.J. R. Cotter). 2. Physical impact of beam trawls on seabed sediments (R. Fonteyne). 3. Is bottom traw3ling partly responsible for the regression of Posidonia oceanica meadows in the Mediterranean Sea (G.D. Ardizzone, P. Tucci, A. Somaschini and A. Belluscio). PART 2: Effects of Fishing on Benthic Fauna and Habitats. 4. Fishing mortality of populations of megafauna in sandy sediments (M.J.N. Bergman and J.W. van Santbrink). 5. Effects of otter trawling on the benthos and environment in muddy sediments (B.Ball, B. Munday and I. Tuck). 6. The effects of scallop dredging on gravelly seabed communities (C. Bradsaw, L.O. Veale, A.S. Hill and A.R. Brand). 7. Impact of scallop dredging on maerl grounds (J.M. Hall--Spencer and P.G. Moore). PART 3: Fishing As A Source of Energy Subsidies. 8. The behavioural response of benthic scavengers to otter--trawling disturbance in the Mediterranean (M. Demestre, P. Sanchez and M.J. Kaiser). 9. Food subsidies generated by the beam--trawl fisher in the southern North Sea (M. Fonds and S. Groenewold). 10. Impact of trawling on populations of the invertebrate scavenger Asterias rubens (K. Ramsay, M.J. Kaiser, A.D. Rijnsdorp, J.A. Craeymeersch and J. Ellis). 11. Seabirds and commercial fisheries: population trends of piscivorous seabirds explained (C.J. Camphysen and S. Garthe). PART 4: Long--Term Changes Associated with Fishing. 12. Distribution of macrofauna in relation to the micro--distribution of trawling effort (J.A. Craeymeersch, G.J. Piet, A.D. Rijnsdorp and J. Buijs). 13. Long--term changes in North Sea Benthos: Discerning the role of fisheries (C.L. J. Frid and R.A. Clark). 14. Effects of fishing on non--target fish species (S.P.R. Greenstreet and S.I. Rogers). 15. Impacts of fishing on diversity: from pattern to process (S. Jennings and J.D. Reynolds). PART 5: Conservation Methods, Issues and Implications for Biodiversity. 16. Technical modifications to reduce the by--catches and impacts of bottom--fishing gears (B.van Marlen). 17. Fishing and cetacean by--catches (N.J.C. Tregenza). 18. Effects of fishing on non--targeted species and habitats: identifying key nature conservation issues (M.L. Tasker, P.A. Knapman and D. Laffoley). 19. The need for closed areas as conservation tools (H.J. Lindeboom). 20. No--take zones: a management context (J.W. Horwood). PART 6: Socio--Economic Implications and Mechanisms for Reducing the Impacts of Fisheries. 21. Economic incentives to discard by--catch in unregulated and individual transferable quotas fisheries (S. Pascoe). 22. Options for the reduction of by--catches of harbour porpoises (Phocoena phocoena) in the North Sea (J.M. McGlade and K.I. Metuzals). 23. Economic and sociocultural priorities for marine conservation (P.J. S. Jones). 24. Integrated management: the implications of an ecosystem approach to fisheries management (D. Dymes). PART 7: Workshop Conclusions. 25. The implications of the effects of fishing on non--targeted species and habitats (M.J. Kaiser). Glossary. Index.

Developmental patterns within a multispecies reef fishery : Management applications for essential fish habitats and protected areas

Abstract: Diverse information sets and regulatory mechanisms are necessary for the management of essential fish habitats (EFH) and protected areas involving multispecies fisheries. We therefore identified key pelagic and demersal developmental patterns among the 73 species of the snapper-grouper complex of the South Atlantic Fishery Management Council. Twenty-two potential spawning aggregation sites for eight snapper species near the Dry Tortugas and Key West were identified by commercial fishermen. Mean larval duration estimates were available for 15 species and ranged from 14 to 75 d. Larval durations for grunts, snappers, and groupers are within the residence times of some gyres. Settlement areas are depth stratified and, settlers often use shallower habitats than adults. Demersal stages of at least 50 species showed some degree of ontogenetic migration across the shelf, but most evidence suggests that strict estuary dependence is a rare lifehistory strategy among the species in the complex; facultative use of estuaries is more common. Including key nursery habitats in protected areas may not safeguard early life stages affected by coastal construction projects unless the design process is coordinated among agencies responsible for water quality and habitat protection through tools such as EFH. Sites that consistently support spawning aggregations for multiple species require management both as EFH-Habitat Areas of Particular Concern and, potentially, as no-take protected areas. The most important known snapper spawning aggregation site in the lower Florida Keys is Riley's Hump. Despite a site closure in May and June, aggregations of several other snapper species are heavily fished later in the year. A year-round closure to protect both fish stocks and remaining habitat integrity is warranted. Coastal development and fishing activities may affect multiple life stages of the same species, although these activities are often managed under different regulatory regimes. The need to unify coastal land management with fishery management was reinforced by the essential fish habitat (EFH) provisions in the reauthorization of the Magnuson-Stevens Act (NOAA, 1996). Accordingly, the South Atlantic Fishery Management Council characterized EFH for species in its jurisdiction (federal waters of North Carolina through the east coast of Florida) in a comprehensive amendment that included seven fishery management plans (SAFMC, 1998a,b). Development of regulatory initiatives for multispecies management units can be confounded by high phylogenetic and ontogenetic variability. This problem is particularly apparent in the Snapper-Grouper Fishery Management Plan, which includes 73 species. The snapper-grouper complex is the most diverse management unit under council jurisdiction, and its species use a broad array of habitats across the entire continental shelf. In addition to the EFH initiative, many researchers and managers now suggest that no-take areas, commonly called marine protected areas or reserves, may be necessary for sustainable fishery management (Plan Development Team, 1990; Allison et al., 1998; Johnson et al., 1999). The council's protected-area work has largely emphasized the snapper-grouper complex.

Marine catchment basin effects versus impacts of fisheries on semi-enclosed seas

Abstract: Synchronous anthropogenic effects on marine coastal systems, particularly since World War II, make it difficult to separate effects of fishing from terrestrial inputs, especially those caused by nutrient runoff. Natural enrichment is vital to productive fisheries, but over the long term anthropogenic nutrient impacts generally predominate over fishery effects in semi-enclosed seas and affect biodiversity and susceptibility to fishing. Such impacts on marine fisheries beyond natural levels of outflow are referred to here as marine catchment basin (MCB) effects. They require coordinated actions within the catchment area to control them, since fisheries management actions alone are unlikely to be effective in rectifying ecosystem impacts. Net nutrient inflows may be positive or negative, depending on intensity and degree of retention by the receiving marine system and may promote ecosystem change and lead to ecological dominance by exotic species. Initially positive effects of enrichment may disguise the urgent need for coordinated environmental and fishery management measures in semi-enclosed seas. Fisheries impacts are serious, but may be secondary and synergistic, but potentially catastrophic under hypoxic conditions since eutrophic processes make demersal ecosystems particularly sensitive to disturbance of bottom habitats. Hence, fishing with bottom gear may impact bottom fauna and demersal resources within or above organic sediments affected by eutrophic processes and hypoxia. These effects show up as changes in the ratio of pelagic to demersal landings, and support broad-brush comparative studies of areas subject to different levels of environmental impact.

Addressing ecosystem effects of fishing using marine protected areas

Abstract: This article is a synthesis of the current literature on the potential of marine protected areas (MPAs) a useful management tool for limiting the ecosystem effects of fishing, including biological and socio-economic aspects There is sufficient evidence that fishing may negatively affect ecosystems Modelling and case studies show that the establishment of MPAs, especially for overexploited populations, can mitigate ecosystem effects of fishing Although quantitative ecosystem modelling techniques incorporating MPAs are in their infancy, their role in exploring scenarios is considered crucial Success in implementing MPAs will depend on how well the biological concerns and the socio-economic needs of the fishing community can be reconciled

Ecosystem approaches to fishery management through essential fish habitat

Abstract: The Magnuson-Stevens Fishery Conservation and Management Act recognizes that fish stocks depend on healthy ecosystems and requires that fishery managers expand their management regimes to include the very basis of healthy fisheries-the habitat itself. The 1996 amendments to this primary United States marine fishery-management law include a new mandate to identify habitats essential to managed living marine resources and to take steps to ensure that those habitats remain healthy and can support sustainable fisheries. Until now, the legislative mandate for protecting habitat for marine and anadromous stocks came through statutes not specifically focused on the needs of commercial and recreational fish species. Now, there is explicit linkage between fishery-management programs, traditionally designed to manage the harvesting activity itself, and efforts to ensure that fishing and nonfishing activities do not undermine the productivity of the stocks. This emphasis on habitat health and productivity brings a broader ecosystem perspective to traditional fishery management.The insertion of essential fish habitat (EFH) provisions into fisheries management has been an enormous undertaking. The agency and the regional fishery management councils, working with other partners, completed the first stage of the process within very tight statutory deadlines. The councils have made use of all of the tools provided them under the act and the EFH regulations, such as designating habitat areas of particular concern (EFH-HAPCs), recommending fishing restrictions within special areas, defining priority research and information needs, and documenting threats and conservation measures appropriate for federal actions that may adversely affect EFH. This effort has entailed a great deal of scientific as well as policy analysis. We are currently implementing the federal consultation process to address threats to fish habitat in a consistent and timely manner.This new habitat thrust will align fishery managers and scientists with new allies in the habitat arena, increasing benefits to marine resource-management programs and fishery management. As suggested by the theme of this issue, an understanding and consideration of marine reserves and other special-area management concepts can benefit federal fishery management. This article gives an overview of how the fishery-management councils are fulfilling the essential fish habitat mandate by using a broader ecosystem approach to conservation that considers the ecological role of managed species, analyzes species' habitat needs from state waters to the high seas, and examines shifts in population health and sustainability over the course of decades.

A multivariate approach for defining fishing tactics from commercial catch and effort data

Abstract: Fishing tactics correspond to fishing practices at the scale of the fishing operation. In the case of mixed fisheries, they are defined as a combination of target species, gear, and fishing locatio...

Fisheries in the Mediterranean

Abstract: The aim of this paper is to give a description of the Mediterranean fisheries, and its level of exploitation and to address the main questions dealing with its management. The Mediterranean is a semi-enclosed marine area with generally narrow continental shelves. The primary production of the Mediterranean is among the lowest in the world (26-50g C m-2 y-1). The Mediterranean fisheries can be broken down into three main categories: small scale fisheries, trawling and seining fisheries, which operated on demersal, small pelagic and large pelagic resources. After a general description of the state of the resources in the different areas of the Mediterranean it is concluded that (a) the overall pictures from the western to the eastern Mediterranean are not considerably different, (b) the total landings in the Mediterranean have been increased the last decades, and (c) from the perspective of stock assessment, the very few available time series data show stable yield levels. In general fisheries management in the Mediterranean is at a rela- tively early stage of development, judging by the criteria of North Atlantic fisheries. Quota systems are generally not applied, mesh-size regulations usually are set at low levels relative to scientific advice, and effort limitation is not usually applied or, if it is, is not always based on a formal resource assessment. The conservation/management measures applied by the Mediterranean countries can be broadly separated into two major categories: those aiming to keep the fishing effort under control and those aiming to make the exploitation pattern more rational. The most acute problems in the management of the Mediterranean resources are the multispecificity of the catches and the lack of reliable official statistics.

Over-exploitation of a broadcast spawning marine invertebrate: Decline of the white abalone

Abstract: Marine invertebrates have long been consideredto be resistant to overfishing. However, agrowing number of exploited taxa have declinedsubstantially and even disappeared from partsof their former range. We consider the case ofthe white abalone (Haliotis sorenseni);the first marine invertebrate proposed for theUS endangered species list. This high-valuespecies was one of five abalones targeted inthe California and Mexico fisheries; it is nowrare and protected from fishing. The biologicalcharacteristics of this deep-living abaloneindicate that it was particularly vulnerable toover-exploitation; reduction of density orgroup size is now known to lead to declines infertilization success and recruitment failure.Warning signs of potential problems existedboth pre- and post-exploitation but were notrecognized. In particular, serial depletion wasnot detected because catch was not analyzedspatially, perhaps because total landings werereasonably stable for the short period ofexploitation. Recent submersible surveys led toestimates that white abalone now number lessthan 2,600 animals or 0.1% of the estimatedpre-exploitation population size. Densities andestimated population sizes are less than 100animals, at all but one location. Alternateexplanations for the decline in abundance wereconsidered and only exploitation-linkedfactors, such as sub-legal mortality andillegal fishing, were likely contributors.Episodic recruitment appears to be acharacteristic of broadcast-spawning,long-lived species and may make themparticularly vulnerable to over-exploitation.Management strategies based on size limits thatallow a few years of spawning prior to reachingminimum legal size are insufficient.Sustainable fisheries will require multipleprotected areas to preserve brood stockaggregations necessary for successfulfertilization.

The enhancement of cod stocks

Abstract: Atlantic cod have been a primary target for marine stock enhancement since the 1880s. In the early part of this period, hatched larvae were released in Norway, the USA and Canada. The last larval releases were conducted in Norway in 1971, and a century of cod larvae releases were halted without any clear evidence of benefit. Since the early 1980s, the focus has been on production of larger, more viable juvenile cod. Emphasis has been given to the design of tag–release programmes involving large-scale releases and ecosystem analysis in selected ecosystems. Most of this research has been carried out in Norway, where more than one million tagged juvenile cod have been released. Smaller stocking experiments have also been performed in Denmark, Sweden, the Faroe Islands and the USA. This paper reviews the major findings from these programmes. We include summaries and evaluations of rearing techniques for juvenile cod, methods of tagging and recapture, experimental fishing, migration, mortality and growth rates in the different habitats, genetic analysis, and ecosystem studies that have tried to describe the variation in the cod carrying capacity of selected release areas. Despite relatively large variation in environmental conditions, in cod production and in fishing mortality along the Norwegian coast, results indicate that, under the conditions experienced during the 1980s and 1990s, releases of juvenile cod did not significantly increase cod production and catches. The biological limitations and future prospects of Atlantic cod stock enhancement are addressed.

Vaquita Bycatch in Mexico's Artisanal Gillnet Fisheries: Driving a Small Population to Extinction

Abstract: The world's most endangered marine cetacean, the vaquita ( Phocoena sinus ), continues to be caught in small-mesh gillnet fisheries throughout much of its range. We monitored fishing effort and inciden- tal vaquita mortality in the upper Gulf of California, Mexico, from January 1993 to January 1995 to study the magnitude and causes of the incidental take. Of those factors studied, including net mesh size, soaktime, and geographic area, none contributed significantly to the incidental mortality rate of the vaquita, implying that the principal cause of mortality is fishing with gillnets per se . The total estimated incidental mortality caused by the fleet of El Golfo de Santa Clara was 39 vaquitas per year (95% CI 5 14, 93), over 17% of the most recent estimate of population size. El Golfo de Santa Clara is one of three main ports that support gillnet fisheries throughout the range of the vaquita. Preliminary results indicate that fishing effort for San Felipe, Baja California, is comparable to that of El Golfo de Santa Clara, suggesting that this estimate of incidental mortality of vaquitas represents a minimum. We strongly recommend a complete and permanent ban on gillnets in the area. Alternative or supplemental mitigation strategies include (1) a maximum annual allow- able mortality limit of vaquitas; (2) mandatory observer coverage of all boats fishing within the Upper Gulf of California and Colorado River Delta Biosphere Reserve; (3) extension of the Upper Gulf of California and Colorado River Delta Biosphere Reserve to encompass all known vaquita habitat; (4) rigorous enforcement of new and existing regulations; and (5) development of alternative sources of income for gillnet fishers.

Angler Responses to Potential Harvest Regulations in a Norwegian Sport Fishery: A Conjoint-Based Choice Modeling Approach

Abstract: Experimental modeling of angler choice behavior is slowly emerging as an alternative to both the modeling of actual fishing behavior (revealed preferences), and the modeling of behavioral antecedents, such as attitudes, beliefs, and opinions. These conjoint-based choice modeling approaches are particularly useful for evaluating various fisheries management alternatives and programs. In this study we applied a discrete choice experiment (DCE), which relies on the principle of fractional factorial designs, to produce hypothetical profiles of fishing opportunities. The study was conducted in Engerdal, eastern Norway. Engerdal is a popular fishing area for locals and tourists from Norway and Sweden. Proper harvest regulation of a popular sport fishery for brown trout Salmo trutta and European grayling Thymallus thymallus is the major challenge to fisheries management in the area. Data were collected in a mail survey in the fall of 1996. Three regulation variables (minimum size limit, bag limit, and b...

An ecosystem-based approach for Alaska groundfish fisheries

Abstract: Witherell, D., Pautzke, C., and Fluharty, D. 2000. An ecosystem-based approach for Alaska groundfish fisheries. – ICES Journal of Marine Science, 57: 771–777. An ecosystem-based approach is being developed for the management of groundfish fisheries in the North Pacific Ocean off Alaska, USA. The approach involves public participation, reliance on scientific research and advice, conservative catch quotas, comprehensive monitoring and enforcement, by-catch controls, gear restrictions, temporal and spatial distribution of fisheries, habitat conservation areas, and other biological and socioeconomic considerations. The basic ecosystem consideration employed is a precautionary approach to extraction of fish resources. Off Alaska, all groundfish stocks are considered healthy, while providing sustained yields of about 2 million tonnes annually. Management measures are also taken to minimize potential impacts of fishing on seafloor habitat and other ecosystem components such as marine mammals and seabirds. 2000 International Council for the Exploration of the Sea

Protection of fish spawning habitat for the conservation of warm-temperate reef-fish fisheries of shelf-edge reefs of Florida

Abstract: We mapped and briefly describe the surficial geology of selected examples of shelfedge reefs (50–120 m deep) of the southeastern United States, which are apparently derived from ancient Pleistocene shorelines and are intermittently distributed throughout the region. These reefs are ecologically significant because they support a diverse array of fish and invertebrate species, and they are the only aggregation spawning sites of gag (Mycteroperca microlepis), scamp (M. phenax), and other economically important reef fish. Our studies on the east Florida shelf in the Experimental Oculina Research Reserve show that extensive damage to the habitat-structuring coral Oculina varicosa has occurred in the past, apparently from trawling and dredging activities of the 1970s and later. On damaged or destroyed Oculina habitat, reef-fish abundance and diversity are low, whereas on intact habitat, reef-fish diversity is relatively high compared to historical diversity on the same site. The abundance and biomass of the economically important reef fish was much higher in the past than it is now, and spawning aggregations of gag and scamp have been lost or greatly reduced in size. On the west Florida shelf, fishers have concentrated on shelf-edge habitats for over 100 yrs, but fishing intensity increased dramatically in the 1980s. Those reefs are characterized by low abundance of economically important species. The degree and extent of habitat damage there is unknown. We recommend marine fishery reserves to protect habitat and for use in experimentally examining the potential production of unfished communities. Ecosystem-oriented and single-species-oriented fishery management are based on very different goals and considerations. Ecosystem management embraces preservation of biodiversity, maintenance of ecosystem structure and function, and broad-scale climatic considerations, whereas single-species management, in practice, is concerned with optimum exploitation of desirable species. Traditional management plans, in this case, involve social, economic, and biological aspects of fisheries but rarely consider the interspecific or physical processes that impinge upon them. A marked departure from this attitude was reflected in the passage of the Magnuson-Stevens Fishery Management and Conservation Act of 1996, which in effect linked the goals of sustainable fishery production and ecosystem preservation by making habitat a central issue in the management of fisheries. Because the act requires the protection and/or restoration of essential fish habitat, it links preservation of habitat with sustainable production of fishery resources and basically encourages the ecosystem approach to fishery management. Habitat is fundamentally important to fishery production because its loss can profoundly affect productivity (Dayton et al., 1995). Benthic trawling and dredging may be especially damaging (Jones, 1992; Kaiser, 1998; Pilskalin et al., 1998; Watling and Norse, 1998), but other practices, such as removal of apex predators (Goeden, 1982) and other ecologically important species (McClanahan et al., 1999), may have equally severe reper

Sustainability of the Lake Superior Fish Community: Interactions in a Food Web Context

Abstract: The restoration and rehabilitation of the native fish communities is a long-term goal for the Laurentian Great Lakes. In Lake Superior, the ongoing restoration of the native lake trout populations is now regarded as one of the major success stories in fisheries management. However, populations of the deepwater morphotype (siscowet lake trout) have increased much more substantially than those of the nearshore morphotype (lean lake trout), and the ecosystem now contains an assemblage of exotic species such as sea lamprey, rainbow smelt, and Pacific salmon (chinook, coho, and steelhead). Those species play an important role in defining the constraints and opportunities for ecosystem management. We combined an equilibrium mass balance model (Ecopath) with a dynamic food web model (Ecosim) to evaluate the ecological consequences of future alternative management strategies and the interaction of two different sets of life history characteristics for fishes at the top of the food web. Relatively rapid turnover rates occur among the exotic forage fish, rainbow smelt, and its primary predators, exotic Pacific salmonids. Slower turnover rates occur among the native lake trout and burbot and their primary prey—lake herring, smelt, deepwater cisco, and sculpins. The abundance of forage fish is a key constraint for all salmonids in Lake Superior. Smelt and Mysis play a prominent role in sustaining the current trophic structure. Competition between the native lake trout and the exotic salmonids is asymmetric. Reductions in the salmon population yield only a modest benefit for the stocks of lake trout, whereas increased fishing of lake trout produces substantial potential increases in the yields of Pacific salmon to recreational fisheries. The deepwater or siscowet morphotype of lake trout has become very abundant. Although it plays a major role in the structure of the food web it offers little potential for the restoration of a valuable commercial or recreational fishery. Even if a combination of strong management actions is implemented, the populations of lean (nearshore) lake trout cannot be restored to pre-fishery and pre-lamprey levels. Thus, management strategy must accept the ecological constraints due in part to the presence of exotics and choose alternatives that sustain public interest in the resources while continuing the gradual progress toward restoration.