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Predation risk on larval gadids by pelagic fish in the Georges Bank ecosystem. I. Spatial overlap associated with hydrographic features

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Abstract:

We investigated the relationship between hydrographic variables on Georges Bank and the spatial distribution of larval Atlantic cod (Gadus morhua), larval haddock (Melanogrammus aeglefinus), and two planktivorous fish, Atlantic herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). We conducted cruises during April-May of 1990, 1994, and 1995 to document spatial distributions and employed logistic regression and a spatial-overlap index to assess relationships between hydrographic variables, spatial distributions and spatial overlap between gadid larvae and planktivorous fish. Cod larvae were more abundant in shallow well-mixed areas, while both haddock larvae and herring were more abundant in stratified areas. Atlantic mackerel occurred in deeper water and had little spatial overlap with the other species. In 1995, the presence of Scotian Shelf water and an intrusion of continental slope water altered temperature and salinity distributions and increased spatial overlap between cod larvae and herring. The stratified areas offer a higher concentration of prey for larval haddock, however there is increased exposure to planktivorous fish predators, creating a potential trade-off between predation and starvation. Due to the high abundance of planktivorous fish and high spatial and temporal overlap, predation is likely an important factor influencing survival of gadid larvae on Georges Bank.

Nous avons étudié la relation entre les variables hydrographiques sur le banc Georges et la répartition spatiale des larves de la Morue franche de l'Atlantique (Gadus morhua), des larves de l'Aiglefin (Melanogrammus aeglefinus) et de deux poissons planctonophages, le Hareng atlantique (Clupea harengus) et le Maquereau bleu (Scomber scombrus). Des croisières en avril-mai en 1990, 1994 et 1995 ont permis d'accumuler des informations sur les distributions spatiales; il a ensuite été possible à l'aide de la régression logistique et d'un indice de chevauchement spatial d'établir les relations entre les variables hydrographiques, les distributions spatiales et le recoupement spatial des larves de gadidés et des poissons planctonophages. Les larves de morue étaient plus abondantes dans les eaux peu profondes et bien brassées, alors que les larves d'aiglefin et les harengs étaient plus nombreux dans les zones stratifiés. Le Maquereau rouge se retrouvait dans les eaux plus profondes et sa répartition recoupait peu celle des autres espèces. En 1995, la présence d'eau provenant de la plate-forme néo-écossaise et une intrusion d'eau provenant du talus continental ont modifié les répartitions de température et de salinité et augmenté le recoupement spatial des larves de morue et des harengs. Les zones stratifiées offrent une plus forte concentration de proies pour les larves d'aiglefin, mais aussi une plus grande exposition aux prédateurs des poissons planctonophages; il se crée donc potentiellement un compromis entre la prédation et la famine. À cause de la forte densité de poissons planctonophages et des forts recoupements spatiaux et temporels, la prédation est vraisemblablement un facteur important dans la survivance des larves de gadidés sur le banc Georges.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2000

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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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