Groundfish

About: Groundfish is a research topic. Over the lifetime, 1070 publications have been published within this topic receiving 23181 citations.

Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations

Abstract: Numerous groundfish stocks in both the Atlantic and Pacific are considered overfished, resulting in large-scale fishery closures. Fishing, in addition to simply removing biomass, also truncates the age and size structure of fish populations and often results in localized depletions. We summarize recent research suggesting that an old-growth age structure, combined with a broad spatial distribution of spawning and recruitment, is at least as important as spawning biomass in maintaining long-term sustainable population levels. In particular, there is evidence that older, larger female rockfishes produce larvae that withstand starvation longer and grow faster than the offspring of younger fish, that stocks may actually consist of several reproductively isolated units, and that recruitment may come from only a small and different fraction of the spawning population each year. None of these phenomena is accounted for in current management programs. We examine alternative management measures that addre...

Community reorganization in the Gulf of Alaska following ocean climate regime shift

Abstract: A shift in ocean climate during the late 1970s triggered a reorganization of community structure in the Gulf of Alaska ecosystem, as evidenced in changing catch composi- tion on long-term (1953-1997) small-mesh trawl surveys. Forage species such as pandalid shrimp and capelin declined because of recruitment failure and predation, and populations have not yet recovered. Total trawl catch biomass declined > 50% and remained low through the 1980s. In contrast, recruitment of high trophic-level groundfish improved during the 1980s, yielding a > 250% increase in catch biomass during the 1990s. This trophic reorganization apparently had negative effects on piscivorus sea birds and marine mammals.

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.

Large-scale disturbance and the structure of marine systems: fishery impacts on georges bank

Abstract: Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production. Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water fleets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water fleets. The implementation of extended jurisdiction (the 200-mile [370.4-km] limit) in 1977 was followed by modernization and increased capacity of the domestic fleet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to h...

Analysis of groundfish survey abundance data: combining the GLM and delta approaches

Abstract: This paper describes a method for the analysis of groundfish survey data by incorporating zero and non-zero values into a single model. This is done by using a model which modifies the delta-distribution approach to fit into the GLM framework and uses maximum likelihood to estimate parameters. No prior assumptions of homogeneity are used for the structure of the zero or non-zero values. The method is primarily applicable to fixed-station designs, although extensions to other designs are possible. The maximum likelihood estimation reduces to fitting a GLM to 0/1 values and another GLM to the positive abundance values. The new model is tested on Icelandic groundfish survey data. It is seen that the model can be used for evaluating the eVect of diVerent factors on catch rates as well as estimating abundance indices. Results from diVerent models are compared on the basis of tuned VPA runs. ? 1996 International Council for the Exploration of the Sea