The effect of light intensity on the availability of walleye pollock (Theragra chalcogramma) to bottom trawl and acoustic surveys

Authors: Kotwicki, Stan; De Robertis, Alex; von Szalay, Paul; Towler, Rick

Source: Canadian Journal of Fisheries and Aquatic Sciences, Volume 66, Number 6, June 2009 , pp. 983-994(12)

Publisher: NRC Research Press

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Abstract:

Quantitative assessment of semidemersal fish such as walleye pollock (Theragra chalcogramma) is difficult because the proportion of walleye pollock available to standardized surveys varies temporally and spatially. The US National Marine Fisheries Service’s Alaska Fisheries Science Center conducts bottom trawl (BT) surveys to estimate the demersal portion of the walleye pollock population and acoustic trawl (AT) surveys to estimate the pelagic portion. Both surveys are conducted during daylight hours to minimize variability due to diel changes in vertical distribution. To test if daytime near-bottom light intensity affects the proportion of walleye pollock available to the BT survey, we concurrently measured light and walleye pollock abundance on the Bering Sea shelf. Logistic regression models demonstrated that both light and depth affected walleye pollock abundance estimates by either BT or AT surveys, with more walleye pollock available to the BT survey under high illumination and at shallow depths and less walleye pollock available to the AT survey under these conditions. This finding suggests that daytime survey catchability for walleye pollock depends on depth and light intensity and that incorporation of light measurements could improve the precision of abundance estimates of semidemersal species such as walleye pollock.

L’évaluation quantitative des poissons semi-benthiques tels que les goberges de l’Alaska (Theragra chalcogramma) est difficile, car la proportion des goberges de l’Alaska accessible aux inventaires standardisés varie dans le temps et l’espace. L’Alaska Fisheries Science Center du US National Marine Fisheries Service mène des inventaires au chalut de fond (BT) afin d’estimer la proportion benthique la population de goberges de l’Alaska et des relevés acoustiques couplés à des inventaires au chalut (AT) pour estimer la proportion pélagique. Les deux inventaires sont réalisés durant les heures d’éclairement pour minimiser la variabilité due aux changements de la répartition verticale au cours de la journée. Afin de vérifier si l’intensité lumineuse près du fond durant la journée affecte la proportion des goberges de l’Alaska accessible à l’inventaire BT, nous avons mesuré simultanément la lumière et l’abondance des goberges de l’Alaska sur la plate-forme de la mer de Béring. Des modèles de régression logistique démontrent que la lumière et la profondeur affectent tous deux l’estimation de l’abondance des goberges de l’Alaska, tant dans les inventaires BT que AT: en conditions d’illumination élevée et de faible profondeur, un plus grand nombre de goberges de l’Alaska est accessible aux inventaires BT et un nombre moins élevé aux inventaires AT. Cette observation fait croire que la capturabilité de la goberge de l’Alaska au cours des inventaires de jour dépend de la profondeur et le l’intensité lumineuse; une incorporation de mesures de la lumière pourrait donc améliorer la précision des estimations d’abondance des espèces semi-benthiques, telles que la goberge de l’Alaska.

Document Type: Research Article

Publication date: June 1, 2009

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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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