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Spatial and temporal variance of walleye pollock (Theragra chalcogramma) in the eastern Bering Sea

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Mobile acoustic surveys attempt to map and count aquatic organisms without biasing abundance estimates. Horizontal and vertical movements by target species may influence density measurements and net samples during acoustic surveys. To investigate the influence of fish movement on density data, we compared temporal and spatial variability of walleye pollock (Theragra chalcogramma) in three sets (2 night, 1 day) of 14.8-km transects in the eastern Bering Sea. Walleye pollock density distributions were also compared with those in the five nearest daytime survey transects. We found that horizontal density distributions did not change at temporal scales ≤4 h and that spatial variance remained consistent at scales ≤2.5 km. Spatial variance density patterns were similar in transects sampled during the day compared with those sampled at night and were also similar in along-shore compared with cross-shore transects. Transects that contained two biological scattering layers could be vertically separated into zooplankton and fish. Spatial variance patterns in the upper zooplankton layer mimicked those of passive tracers, while patterns in the lower layer were consistent with those previously observed for mobile nekton. Current sampling resolution of acoustic surveys adequately captures horizontal spatial variance of walleye pollock in the Bering Sea.

Les inventaires acoustiques mobiles cherchent à cartographier et à dénombrer les organismes aquatiques sans fausser les estimations d'abondance. Les déplacements horizontaux et verticaux des espèces ciblées peuvent affecter les mesures de densité et fausser les échantillons nets durant l'inventaire. Afin d'évaluer l'influence des déplacements des poissons sur les données de densité, nous avons comparé la variation temporelle et spatiale chez des goberges de l'Alaska (Theragra chalcogramma) dans trois séries (2 de nuit et 1 de jour) de transects de 14,8 km dans l'est de la mer de Béring. Nous avons aussi comparé les répartitions de densité des goberges de l'Alaska à celles obtenues sur les cinq transects d'inventaires de jour les plus proches. Les répartitions horizontales de densité ne changent pas aux échelles temporelles de ≤4 h et la variance spatiale reste uniforme aux échelles de ≤2,5 km. Les patrons de variance de la densité spatiale sont semblables sur les transects inventoriés le jour et la nuit, de même que chez ceux faits parallèlement et perpendiculairement à la rive. Dans les transects qui contiennent deux couches de diffusion biologique, nous pouvons distinguer verticalement le zooplancton et les poissons. Les patrons de variance spatiale de la couche supérieure de zooplancton imitent ceux de traceurs passifs, alors que les patrons de la couche inférieure concordent avec ceux observés antérieurement chez le necton mobile. La résolution actuelle de l'échantillonnage des inventaires acoustiques permet de capter de façon adéquate la variance spatiale horizontale de la goberge de l'Alaska dans la mer de Béring.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2005-12-01

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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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