Nutrient loading by anadromous alewife (Alosa pseudoharengus): contemporary patterns and predictions for restoration efforts

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Abstract:

Anadromous alewives (Alosa pseudoharengus) have the potential to alter the nutrient budgets of coastal lakes as they migrate into freshwater as adults and to sea as juveniles. Alewife runs are generally a source of nutrients to the freshwater lakes in which they spawn, but juveniles may export more nutrients than adults import in newly restored populations. A healthy run of alewives in Connecticut imports substantial quantities of phosphorus; mortality of alewives contributes 0.68g P·fish–1, while surviving fish add 0.18g P, 67% of which is excretion. Currently, alewives contribute 23% of the annual phosphorus load to Bride Lake, but this input was much greater historically, with larger runs of bigger fish contributing 2.5 times more phosphorus in the 1960s. A mesocosm experiment in a nearby lake showed that juvenile alewife growth is strongly density dependent, but early survival may be too low for juvenile outmigration to balance adult inputs. In eutrophic systems where nutrients are a concern, managers can limit nutrient loading by capping adult returns at a level where juvenile populations would not be suppressed.

Les gaspareaux (Alosa pseudoharengus) anadromes peuvent potentiellement modifier les bilans de nutriments des lacs côtiers pendant leurs migrations adultes vers les eaux douces et leurs migrations juvéniles vers la mer. Les montaisons de gaspareaux sont généralement des sources de nutriments pour les lacs d'eau douce dans lesquels ils fraient, mais, dans les populations nouvellement rétablies, les jeunes peuvent exporter plus de nutriments que les adultes n'en importent. Une montaison saine au Connecticut importe des quantités importantes de phosphore; la mortalité des gaspareaux fournit 0,68g P·poisson–1, alors que les poissons survivants apportent 0,18g P, dont 67% est de l'excrétion. Actuellement, les gaspareaux fournissent 23% de la charge annuelle de phosphore du lac Bride, mais cet apport était beaucoup plus élevé dans le passé lorsque, durant les années 1960, des montaisons plus importantes de poissons plus grands fournissaient 2,5 fois plus de phosphore. Une expérience en mésocosme dans un lac adjacent montre que la croissance des gaspareaux est fortement reliée à la densité, mais que la survie au début du cycle est peut-être trop faible pour que l'émigration des jeunes contrebalance les apports des adultes. Dans les systèmes eutrophes dans lesquels les gestionnaires se préoccupent des nutriments, ceux-ci peuvent contrôler la charge de nutriments en limitant les retours d'adultes au niveau nécessaire pour que les populations de jeunes ne soient pas réduites.

Document Type: Research Article

Publication date: August 1, 2010

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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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