Optimal allocation of effort in studies using the size‐frequency method of estimating secondary production

Heisey, Dennis M.; Hoenig, John M.

doi:10.4319/lo.1986.31.1.0211

Cited by 3 publications

(1 citation statement)

References 5 publications

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“…Pennington, 1986;Smith, 1988b;McConnaughey and Conquest, 1993) or modifying aspects of the survey design (e.g. Francis, 1984;Heisey and Hoenig, 1986;Gavaris and Smith, 1987;Jolly and Hampton, 1990;Smith and Gavaris, 1993). Smith (1990) discussed the application of statistical models and their specific estimators to survey data, and showed that biased estimates can easily result from such an approach (see also Jolly and Hampton, 1990;Myers and Pepin, 1990).…”

Section: Introductionmentioning

confidence: 99%

Associations between Atlantic cod (Gadus morhua) and hydrographic variables: implications for the management of the 4VsW cod stock

Smith

Page

1996

ICES Journal of Marine Science

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Many groundfish stocks on the Atlantic coast of North America are monitored by bottom trawl surveys which use a stratified random design. The resulting estimates of abundance often exhibit high variability within and between surveys, particularly on inter-annual time scales, and inconsistencies in the estimates of relative year-class strength over time. These inconsistencies, or year-effects, may reflect changes in the distribution or catchability of the fish that may be related in turn to environmental factors such as water temperature and salinity. The estimates of cod abundance derived from the research vessel trawl surveys conducted in July over the eastern Scotian Shelf in NAFO areas 4Vs and 4W from 1970-1993 are shown to exhibit these features. Analyses of these survey data also show that cod exhibit age-and areaspecific associations with near-bottom water temperature and salinity ranges that are consistent with the properties of a Cold Intermediate Layer (CIL) water mass in the area and that inter-annual variability in the estimates of abundance is correlated with the area of the bottom found within the CIL. A model relating the variability in the CIL to the estimates of age-specific cod abundance obtained from the surveys was used to derive new survey indices of abundance. These new indices do not have detectable year-effects and may provide more consistent estimates of true relative year-class strength than the original time series.1996 International Council for the Exploration of the Sea

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Section: Introductionmentioning

confidence: 99%

Associations between Atlantic cod (Gadus morhua) and hydrographic variables: implications for the management of the 4VsW cod stock

Smith

Page

1996

ICES Journal of Marine Science

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Estimating total abundance of a large temperate-reef fish using visual strip-transects

1987

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Improving the Precision of Abundance Estimates of Eastern Scotian Shelf Atlantic Cod from Bottom Trawl Surveys

Smith

Gavaris

1993

North American Journal of Fisheries Management

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Abundance estimates from bottom trawl surveys are important elements in the evaluation of stock status. The reliability of stock assessment results are greatly influenced by the precision of the survey abundance estimates. In this study, a new stratified random design, based upon historical spatial distribution, for estimating the abundance of ages 5-12 Atlantic cod Gadus morhua on the eastern Scotian Shelf off Nova Scotia was evaluated. Gains in precision from the new design, relative to simple random sampling, were mainly due to the improved allocation of trawl sets to strata, whereas the gains solely due to the new stratification scheme were minimal. We conclude that any reasonable stratification scheme that is flexible enough to allow for the optimization of the allocation of sets to strata should perform well. In our study, the allocation scheme was based upon the historical spatial distribution of abundances. Although annual changes in spatial distribution would require revision of the allocation strategy, we found that averaging results over several earlier years was more robust than just using the most recent year's data. The new design has been used for an annual March survey of this Atlantic cod stock from 1986 to the present. Comparisons of the results from the 1986-1990 period with those from 1979-1984, which stemmed from the traditional depth-based stratification, indicate that the new design is more efficient with respect to gain in precision than the old design. Finally, we note that the simple random sampling variance is smaller in a July series of surveys of this stock than in the March series and this difference can be exploited to give more precise stratified surveys in July than in March.

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Optimal allocation of effort in studies using the size‐frequency method of estimating secondary production

Cited by 3 publications

References 5 publications

Associations between Atlantic cod (Gadus morhua) and hydrographic variables: implications for the management of the 4VsW cod stock

Associations between Atlantic cod (Gadus morhua) and hydrographic variables: implications for the management of the 4VsW cod stock

Estimating total abundance of a large temperate-reef fish using visual strip-transects

Improving the Precision of Abundance Estimates of Eastern Scotian Shelf Atlantic Cod from Bottom Trawl Surveys

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