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The impact of double-crested cormorant (Phalacrocorax auritus) predation on anadromous alewife (Alosa pseudoharengus) in south-central Connecticut, USA

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The decline of anadromous alewife (Alosa pseudoharengus) threatens an important recreational and commercial fishery. While the cause of this decline is uncertain, predators could be trapping alewives at low abundance by preying on them during spawning migrations. Here we investigate the impact of predation by double-crested cormorants (Phalacrocorax auritus) on spawning adult alewives in south-central Connecticut, USA. We use a bioenergetic model together with estimates of cormorant diets and cormorant and alewife population sizes to estimate the consumption of alewives by cormorants both in Bride Lake, Connecticut, and regionally. We find that cormorants are important predators of spawning adult alewives at Bride Lake but do not have a notable impact on alewife mortality or population size. We also find that cormorants have little effect on alewife populations across south-central Connecticut because few alewives are consumed away from Bride Lake. We conclude that cormorants are important predators for anadromous alewives, but do not pose an immediate threat to the recovery of regional alewife stocks.

Le déclin de gaspareau anadrome (Alosa pseudoharengus) menace une importante pêche sportive et commerciale. Bien que la cause du déclin soit incertaine, les prédateurs pourraient s’emparer des gaspareaux dans les conditions de basse densité en les capturant durant leur migration de fraie. Nous examinons ici la prédation par les cormorans à aigrettes (Phalacrocorax auritus) sur les gaspareaux adultes en fraie dans le centre-sud du Connecticut, É.-U. Un modèle bioénergétique combiné à des estimations du régime alimentaire des cormorans et des densités des populations de cormorans et de gaspareaux nous a servi à estimer la consommation de gaspareaux par les cormorans à la fois dans le lac Bride, Connecticut, et dans la région avoisinante. Les cormorans sont d’importants prédateurs de gaspareaux adultes pendant la fraie au lac Bride, mais ils n’ont que peu d’effet marqué sur la mortalité ou la taille de la population de gaspareaux. Les cormorans ont aussi peu d’effet sur les populations de gaspareaux dans tout le centre-sud du Connecticut, parce que peu de gaspareaux y sont consommés sauf au lac Bride. En conclusion, les cormorans sont d’importants prédateurs des gaspareaux anadromes, mais ils ne représentent pas une menace immédiate pour la récupération des stocks régionaux de gaspareaux.

Document Type: Research Article

Publication date: 2009-02-01

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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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