Effect of Allocation and Stratification Strategies on Precision of Survey Abundance Estimates for Atlantic Cod (<i>Gadus morhua</i>) on the Eastern Scotian Shelf

Gavaris, Stratis; Smith, Stephen J.

doi:10.2960/j.v7.a16

Cited by 34 publications

(34 citation statements)

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“…The spatial distribution of American lobster is influenced by many factors such as temperature (Aiken and Waddy, 1986), salinity (Jury et al, 1994), and shelter availability (Wahle and Steneck 1991) and it differs greatly by season, sex, and size class (Chen et al, 2006). Chang et al, (2010) developed a habitat modeling approach for quantifying season-, size-, and sex-specific lobster distribution in the Gulf of Maine.…”

Section: Simulation Of a "True" Populationmentioning

confidence: 99%

“…For a stratified random designed survey, many studies revealed that optimizing either sample allocation schemes or stratification schemes could lead to an increased precision of survey means or total estimates (Folmer and Pennington, 2000;Gavaris and Smith, 1987;Smith and Tremblay, 2003). There are many methods for allocating samples among strata, the most common being to allocate samples in proportion to strata area/size.…”

Section: Introductionmentioning

confidence: 99%

“…Stratified random sampling approaches are commonly adopted in periodic fishery-independent surveys for tracking the temporal trend of abundance and estimating the total abundance at the defined spatial scale (Gavaris and Smith, 1987). Stratified designs can spread the sampling effort over the study area to improve the precision of estimates especially when there are heterogeneities between strata and homogeneities within a stratum (Lohr, 2009).…”

Section: Introductionmentioning

confidence: 99%

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IAn evaluation of an inshore bottom trawl survey design for American lobster (Homarus americanus) using computer simulations

Cao

Chen²,

Chang³

et al. 2014

J. Northw. Atl. Fish. Sci.

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. 2014. An evaluation of an inshore bottom trawl survey design for American lobster (Homarus americanus) using computer simulations. J. Northw. Atl. Fish. Sci., 46: 27-39. doi:10.2960/J.v46.m696 Abstract This paper evaluates the performance of six possible sampling designs to estimate the population abundance index for American lobster using computer simulations. These designs include simple random sampling (SRS), systematic sampling (SYS) and stratified random sampling with four stratification schemes (i.e., based on region, depth, sediment and region × depth). For the stratified random design with region and depth being used for stratification, we evaluated the performances of different strategies for allocating sampling efforts. Simulations were implemented on the "true" populations which were estimated annually from 2002 to 2008 for both spring and fall based on a general additive model model developed in a separate study. Relative Estimation Error (REE), Relative Bias (RB) and design effect were used to measure the precision, accuracy and efficiency of mean estimation for different designs. On average, SYS tended to yield the most precise and efficient estimate of mean with specified sample size. However, its estimates tended to be biased and its performance varied with sample sizes and realizations of "true" population, thus changed with lobster distribution. Appropriate stratification, such as using depth to determine strata, significantly improved the precision and efficiency over SRS. Sediment, which is related to lobster distribution, was found to have little contribution to the improvement of the performance over SRS when it is used to determine strata. Also, allocating samples to each stratum based on variance or mean of previous year improved precision and efficiency. This study suggests that current design (i.e., region-depth stratified design) used in the survey had stable performance across years and seasons.

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Section: Simulation Of a "True" Populationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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IAn evaluation of an inshore bottom trawl survey design for American lobster (Homarus americanus) using computer simulations

Cao

Chen²,

Chang³

et al. 2014

J. Northw. Atl. Fish. Sci.

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“…The correct design-based approach in this situation is to use cluster sampling formulas, with the transect being the primary unit and the integrated segments of cruise track (referred to as EDSUs in some literature) as secondary units. Key works on the design of hydroacoustic surveys include Francis (1984), Gavaris and Smith (1987), Jurvelius and Auvinen (1989), and Jolly and Hampton (1990). A special ICES workshop held in 1992 (ICES, 1993) reviewed designand model-based approaches for hydroacoustic stock assessment.…”

Section: Design-based Methods For Hydroacoustic Surveysmentioning

confidence: 99%

The use of adaptive cluster sampling for hydroacoustic surveys

Conners

Schwager

2002

ICES Journal of Marine Science

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Resource managers are often required to estimate the size of a wildlife population based on sampling surveys. This problem is especially critical in fisheries, where stock-size estimation forms the basis for key policy decisions. This study looks at design-based methods for a hydroacoustic fisheries survey, with the goal of improving estimation when the target stock has a patchy spatial distribution. In particular, we examine the efficiency and feasibility of a relatively new design-based method known as adaptive cluster sampling (ACS). A simulation experiment looks at the relative efficiency of ACS and traditional sampling designs in a hydroacoustic survey setting. Fish densities with known spatial covariance are generated and subjected to repeated sampling. The distributions of the different estimators are compared.Hydroacoustic data frequently display strong serial correlation along transects and so traditional designs based on one-stage cluster sampling are appropriate. Estimates of total stock size for these designs had a markedly skewed distribution. ACS designs performed better than traditional designs for all stocks with small-scale spatial correlation in fish density, yielding estimates with lower variance. ACS estimators were not skewed and had a lower frequency of large errors. For the most variable stock the use of ACS reduced the coefficient of variation (CV) of the stock size estimate from over 0.9 to around 0.5. Differences between traditional and ACS designs were consistent over multiple realizations of each spatial covariance model.A survey of rainbow smelt (Osmerus mordax) in the eastern basin of Lake Erie was used as a case study for development of a survey design. A field trial showed that use of ACS for the survey is feasible but pointed out some areas for further research. The biggest drawback to use of ACS is uncertainty in the final sample size. This can be partially controlled by applying ACS within a stratified design. ACS retains the unbiased and non-parametric properties of design-based estimation but allows increased sampling in high-density areas that are of greater biological interest. For stocks with an aggregated or patchy spatial distribution ACS can provide a more precise estimate of stock size than traditional survey methods.

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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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Effect of Allocation and Stratification Strategies on Precision of Survey Abundance Estimates for Atlantic Cod (Gadus morhua) on the Eastern Scotian Shelf

Cited by 34 publications

References 1 publication

IAn evaluation of an inshore bottom trawl survey design for American lobster (Homarus americanus) using computer simulations

IAn evaluation of an inshore bottom trawl survey design for American lobster (Homarus americanus) using computer simulations

The use of adaptive cluster sampling for hydroacoustic surveys

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

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