Optimum Size of Sampling Unit for Estimating the Density of Marine Populations

Pennington, Michael; Vølstad, Jon Helge

doi:10.2307/2532157

Cited by 46 publications

(20 citation statements)

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“…Defining the sampling frame is a critical issue in a fishery-independent survey. For example, the size of sampling unit can influence the performance of certain sampling designs (Pennington and Volstad 1991). In this study the sampling unit was defined as 1NM × 1NM and some potential sampling units were excluded due to the operability of gear type.…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

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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“…A logarithmic rather than a linear scale is used, because for marine catch data the variance is often proportional to the square of the mean (Pennington 1983;Pennington and Vølstad 1991) and a logarithmic transformation will consequently stabilize the variance (Snedecor and Cochran 1980). The experimental design was roughly balanced (Table 1) and the model (eq.…”

Section: Data Analysesmentioning

confidence: 99%

Effects of seismic shooting on local abundance and catch rates of cod ((Gadus morhua) and haddock )(Melanogrammus aeglefinus)

Engås¹,

Løkkeborg²,

Ona³

et al. 1996

Can. J. Fish. Aquat. Sci.

169

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Abstract:To determine whether seismic exploration affected abundance or catch rates of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), acoustic mapping and fishing trials with trawls and longlines were conducted in the central Barents Sea 7 days before, 5 days during, and 5 days after seismic shooting with air guns. Seismic shooting severely affected fish distribution, local abundance, and catch rates in the entire investigation area of 40 × 40 nautical miles.Trawl catches of cod and haddock and longline catches of haddock declined on average by about 50% (by mass) after shooting started, which agreed with the acoustic abundance estimates; longline catches of cod were reduced by 21%. Reductions in catch rates were observed 18 nautical miles from the seismic shooting area (3 × 10 nautical miles), but the most pronounced reduction occurred within the shooting area, where trawl catches of both species and longline catches of haddock were reduced by about 70% and the longline catches of cod by 45%; a relatively greater reduction was found (in catches and acoustic estimates) for large (>60 cm) than for small fish. Abundance and catch rates did not return to preshooting levels during the 5-day period after seismic shooting ended.Résumé : Pour déterminer si l'exploration sismique nuit à l'abondance de la morue (Gadus morhua) et de l'églefin (Melanogrammus aeglefinus) ainsi qu'au taux de capture de ces espèces, on a procédé à des travaux de cartographie acoustique et à des essais de pêche au chalut et à la palangre dans la partie centrale de la mer de Barents 7 jours avant, 5 jours durant et 5 jours après une série de tirs sismiques au canon pneumatique. Les tirs ont considérablement modifié la répartition du poisson, abaissé sa densité locale et gravement réduit le taux de capture dans l'ensemble de la région d'étude (soit un secteur mesurant 40 milles marins de côté). En moyenne, les prises de morue et d'églefin au chalut et les prises d'églefin à la palangre ont diminué d'environ 50% (en masse) après que la série de tirs ait commencé. Ces résultats concordent avec ceux des relevés acoustiques d'abondance. Les prises de morues à la palangre ont été réduites de 21%. Des baisses des taux de prise ont été observées jusqu'à 18 milles marins du secteur des tirs sismiques (un secteur de 3 × 10 milles marins), mais l'effet le plus prononcé a été observé à l'intérieur de ce secteur : les prises au chalut des deux espèces et les prises à la palangre de l'églefin ont diminué d'environ 70%, les prises de morue à la palangre d'environ 45%. La réduction est proportionnellement plus marquée dans le cas des poissons de grande taille (>60 cm) que celle des poissons de petite taille, tant dans les prises que dans les estimations par relevé acoustique. Cinq jours après la fin des tirs sismiques, l'abondance et les taux de capture ne s'étaient pas encore rétablis. [Traduit par la Rédaction]

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“…Third, there is a feeling that only using daytime measurements is tantamount to throwing away valuable information and not exploiting the measurements in an adequate way. Survey vessel time is expensive and optimal use of available resources is crucial for the quality of the survey results (Pennington and Vølstad 1991).…”

Section: Introductionmentioning

confidence: 99%

Diurnal variation in bottom trawl survey catches: does it pay to adjust?

Hjellvik¹,

Godø²,

Tjøstheim³

2002

Can. J. Fish. Aquat. Sci.

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Abstract:The diurnal bias of bottom trawl survey catches is studied with the purpose of adjusting for it and thereby improving the accuracy of abundance estimates. The correction term is estimated with uncertainty and thus increases the variance of the resulting abundance estimate. To investigate this adequately, we use a stochastic model describing diurnal fluctuations and examine the annual variation of the diurnal amplitude as a function of species and length. The diurnal amplitude is fairly stable for large fish, and for these, the bias-corrected estimate leads to a moderate increase in variance. For small fish, the diurnal amplitude is unstable, however, and the correction of diurnal bias occurs at the expense of a large increase in variance. This unstable amplitude also leads to a large year-to-year variation in catchability for small fish. For haddock (Melanogrammus aeglefinus), the diurnal amplitude depends heavily on fish length, indicating a strong decrease in catchability with decreasing fish length.Résumé : Nous avons étudié l'erreur systématique reliée à la période de la journée dans les inventaires faits à partir de récoltes au chalut de fond dans le but de trouver un ajustement et ainsi améliorer les estimations d'abondance. L'estimation du terme de correction comporte de l'incertitude, ce qui augmente la variance des estimations d'abondance. Un modèle stochastique qui décrit les fluctuations diurnes et l'examen de la variation annuelle de l'amplitude diurne en fonction des espèces et des longueurs nous ont permis d'étudier ce problème adéquatement. L'amplitude diurne est assez stable chez les gros poissons et, pour eux, une estimation corrigée entraîne une augmentation modeste de la variance. Pour les petits poissons, cependant, l'amplitude diurne est instable et toute correction de l'erreur amène une importante augmentation de la variance. Cette amplitude instable cause aussi une grande variation inter-annuelle de la capturabilité des petits poissons. Chez l'Aiglefin (Melanogrammus aeglefinus), l'amplitude diurne est fortement reliée à la longueur des poissons, avec une forte décroissance de la capturabilité en fonction de la diminution de la longueur du poisson.[Traduit par la Rédaction] Hjellvik et al. 48

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Optimum Size of Sampling Unit for Estimating the Density of Marine Populations

Cited by 46 publications

References 2 publications

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

Effects of seismic shooting on local abundance and catch rates of cod ((Gadus morhua) and haddock )(Melanogrammus aeglefinus)

Diurnal variation in bottom trawl survey catches: does it pay to adjust?

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