Use of Known-Biomass Production Models to Determine Productivity of West Coast Groundfish Stocks (original) (raw)
Related papers
In Search of Optimal Harvest Rates for West Coast Groundfish
North American Journal of Fisheries Management, 2002
In this paper, I explore how patterns of compensatory mortality, as assessed through stock-recruitment relationships, may influence optimal harvest rates and relative yields for several West Coast groundfish stocks. To do this, I revisited Clark's (1991) groundfish life history model and maximin (i.e., maximize the minimum) yield approach to evaluate target harvest rates for five stocks (Dover sole Microstomus pacificus, lingcod Ophiodon elongatus, sablefish Anoplopoma fimbria, Pacific hake Merluccius productus, and widow rockfish Sebastes entomelas) using recent estimates of fishery and life history parameters and stock-recruitment data. I found that a spawningstock-per-recruit target of roughly 35% of its unfished amount would be reasonable for these stocks if Clark's assumed stock-recruitment parameters are representative and the policy goal is a maximin yield. In contrast, use of estimated stock-recruitment parameters suggested more conservative percentages of the unfished spawning stock per recruit and more conservative harvest rate targets for most stocks. A key implication of this work is that Clark's groundfish life history model is sensitive to the stock-recruitment shape parameters. As a result, these parameters should be estimated where possible or imputed using results from meta-analyses. Overall, a conservation target of roughly 35% of the unfished spawning stock per recruit is very likely too low for lingcod, sablefish, and widow rockfish stocks under current environmental conditions, but it may be adequate for Dover sole and Pacific hake stocks.
The Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006 requires Regional Fishery Management Councils to set annual catch limits for all stocks or stock complexes in Federal fishery management plans beginning in 2011. Most species listed in the Pacific Coast Groundfish Fishery Management Plan have not been assessed, in large part due to data limitations. Estimates of sustainable yield for many these species were previously based on undocumented, ad-hoc analyses. We present estimates of sustainable yield for 50 of these stocks using two recently developed models designed to inform management of data-poor stocks. These models rely on recently reconstructed time series of historical catch for west-coast groundfish species and species-specific information related to stock productivity. For this set of data-poor stocks, recent landings statistics reflect shifts in the relative importance of certain species to west-coast fisheries (e.g. increased catches of nearshore and slope rockfish species relative to shelf species), largely due to recent regulatory actions. We provide estimates of overfishing limits (OFLs) for each of the 50 stocks along with comparisons to recent catch levels. Our results suggest that status quo harvest levels range from light exploitation of some stocks to potential overfishing of others. This information could help inform decisions regarding prioritization of future stock assessments for unassessed species. OFLs are expressed as probability distributions, reflecting our uncertainty in model parameters. We select median values as point estimates of OFL, as this statistic is most consistent with National Standard 1 guidelines.
Failure to eliminate overfishing and attain optimum yield in the New England groundfish fishery
ICES Journal of Marine Science, 2014
Under US law, fishery management is required to eliminate overfishing and attain optimum yield (OY). In New England, many groundfish stocks continue to be overfished, and the fishery continues to harvest less than OY. The reasons for the shortfalls are rooted in the socioeconomic structure of the management regime, and technical and scientific issues that constrain the management system. The most recent change in the management regime (days-at-sea to catch shares) and performance relative to OY and the prevention of overfishing are analyzed along with metrics used to gauge performance. The commonly used age-based production model gives a problematic perception of stock abundance. Structural issues that seem to impair achieving OY are the adherence to the single-species interpretation of multiplespecies yield and the use of the F x% proxy. Simpler approaches to stock assessment are discussed. A management system that creates feasible goals and uses improved and simpler metrics to measure performance is needed to facilitate attainment of management goals.
Goals and strategies for rebuilding New England groundfish stocks
Fisheries Research, 2008
Rebuilding depleted fishery resources is a worldwide problem. In the U.S., the Magnuson Stevens Fishery Conservation and Management Reauthorization Act (MSRA) of 2007 requires that "Conservation and management measures shall prevent overfishing while achieving, on a continuing basis, the optimum yield from each fishery.. .". However, translating this legal mandate into tangible goals and actions presents several technical challenges, especially for resources that have been chronically over-exploited. For example, maximum sustainable yields and biomass reference points are poorly estimated for stocks that have been overfished for a long period of time and are poorly defined unless sufficient data are available from periods of low-fishing mortality rates and relatively high-stock sizes. The conundrum of how to set meaningful rebuilding goals given limited information on the population dynamics and trophic interactions of a rebuilt stock can generally be addressed through adaptive management procedures incorporating learning about density-dependent population dynamics. Monitoring changes in life history parameters and recruitment is critical for successful rebuilding strategies realizing the full yield potential of rebuilt stocks while periodic re-evaluation of rebuilding targets is also needed to address uncertainties due to density dependence, trophic interactions or environmental factors. This paper summarizes the development and implementation of goals and strategies to rebuild New England groundfish stocks over the past decade. Management is particularly challenging because the true yield and population size potentials of these interacting stocks is unknown due to chronic overfishing throughout the modern history of the fishery, uncertainty in compensatory/depensatory population dynamics and in the degree of stationarity in environmental control of groundfish recruitment.
Journal of Northwest Atlantic Fishery Science, 1996
A discrete time model was developed to evaluate yield and spawning stock biomassper-recruit and yield-per-unit-effort for a cohort of an idealized groundfish. This fish was characterized as relatively long lived (M = 0.2), slow growing (K = 0.2), with maximum length and weight of 100 cm and 10 kg, respectively, and 50% maturity at a relatively early age of 3 years. The size selection characteristics of trawls and hooks were described by a logistic cumulative distribution function (LCDF) with a range of L 50 and steepness values. The size selection characteristics of gillnets and traps were described by a scaled normal probability density function (NPDF) with a range of values for L opt and the standard deviation.
Canadian Journal of Fisheries and Aquatic Sciences, 2016
Projections are used to explore scenarios for catch advice and rebuilding and are an important tool for sustainably managing fisheries. We tested each projection specification for 12 groundfish stocks in the Northwest Atlantic to identify sources of bias and evaluate techniques for reducing bias. Projections were made from assessments using virtual population analysis (VPA) with 1–7 years of recent data removed from the full time series and were then compared with results from a VPA assessment on the full time series of data. The main source of bias in projections was the assessment model estimates of the numbers at age in the terminal model year + 1 (Na,T+1). Recruitment was responsible for more bias in projections beyond 3 years, when population numbers begin to be dominated by cohorts that were statistically generated. Retrospective analysis was performed and several adjustment factors to reduce bias were tested. Even after adjusting for bias, the remaining bias in projections wa...
Canadian Journal of Fisheries and Aquatic Sciences, 1992
Numerical definition of species caught together by the groundiish trawl fishery operating off the Oregon and Washington coasts during 1985-87 indicated six major assemblages of species. Observers on commercial vessels. recorded data allowing estimation of the weights of commercially important species caught in each tow. Assemblages were selected based on consistencies in three types of analysis of the species weights: detrended correspondence ordination, two-way indicator species clustering, and Bray-Curtis group average clustering. Two of the assemblages were dominated by a single species, one consisting largely of smooth pink shrimp (Pandalus jordani) and the other primarily of widow rockfish (Sebastes entornelas). The other assemblages identified were a deepwater rockfish assemblage, a deepwater Dover sole assemblage, a nearshore mixed-species assemblage, and a bottom rockfish assemblage. These assemblages of commercially cooccurring species may be treated as units in developing mixed-species management plans. The deepwater rockfish assemblage we identify has not been previously described. La definition numerique des especes capturees par les chalutiers qui pechaient le poisson de fond au large des cBtes des Etats de I'Oregon et de Washington au cours de la periode 1985-1987 a indique six assemblages d'especes principaux. Des observateurs se trouvant sur des navires commerciaux ont releve des donnees permettant I'estimation des poids des especes commercialement irnportantes capturees dans chaque trait. Les assemblages ont ete choisis en fonction de la conformite dans trois types d'analyse des poids des especes : ordination de correspondance a tendance temporelle Climtnee, groupement des especes a tndicateur double et groupement de moyenne de groupe de Bray-Curtis. Deux des assemblages etaient domines par une seule esp@ce, un consistant largement en crevettes oceaniques (Pandalus jordani) et I'autre principalement en veuves (Sebastes entornelas). Les autres assemblages identifies etaient : un assemblage de sebaste d'eau profonde, un assemblage de sole de Douvres d'eau profonde, un assemblage d'especes melangees situ6 pres du rivage et un assemblage de sebaste de fond. Ces assemblages d'esp&es presentes commercialement presentes simultanement peuvent @[re traites comme des unites dans I'elaboration de plans de gestion d'especes melang&s. L'assemblage de sebaste d'eau profonde que nous avons identifie n'avait pas ete decrit prkedemment.
2015
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