Estimating abundance from gillnet samples with application to red drum (Sciaenops ocellatus) in Texas bays

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Abstract:

A model of gillnet selection is developed to accommodate the possibility that some catch observations will be known more precisely than others and allow for nonlinear relationships between the selection parameters and mesh size. The model is used to show that gillnet selection for red drum (Sciaenops ocellatus) in Texas bays may be explained as a unimodal process approximating a skewed Laplace distribution, where the optimal length varies in proportion to mesh size and the variance in proportion to the optimal length. It is also suggested that the number of encounters with the net ought to depend on swimming speed of the quarry, which in turn varies predictably with length. This information, along with the estimates of selection, is used to develop indices of abundance for each length-class. The results indicate that the recruitment of year-old red drum to Texas bays has fluctuated markedly since 1975, but without any persistent trends. However, the survival of these and older fish has increased dramatically owing to various regulations promulgated since 1981.

Un nouveau modèle de sélection des filets maillants permet de tenir compte de la possibilité que certaines observations de captures soient plus précises que d'autres et qu'il y ait des relations non-linéaires entre les paramètres de sélection et la dimension de la maille du filet. Le modèle est utilisé pour démontrer que la sélection exercée par les filets maillants sur le tambour rouge (Sciaenops ocellatus) des baies du Texas s'explique comme un processus unimodal s'approchant d'une distribution de Laplace asymétrique dans laquelle la logueur optimale varie en proportion de la dimension de la maille et la variance, en fonction de la longueur optimale. Nous avançons aussi l'hypothèse que le nombre de rencontres avec le filet dépend de la vitesse de nage de la proie, qui est, elle-même, fonction de sa longueur. Ces renseignements, ajoutés aux estimations de sélection, nous ont permis de calculer des indices d'abondance pour chaque classe de longueur. Il en ressort que le recrutement des tambours rouges de 1 an dans les baies du Texas a fluctué de façon importante depuis 1975, mais sans tendance bien marquée. Néanmoins, la survie de ces poissons et celle des poissons plus âgés a augmenté de façon spectaculaire à cause de diverses réglementations en vigueur depuis 1981.

Document Type: Research Article

Publication date: April 1, 2002

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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