PHOSPHORUS REGENERATION BY LAKE-MICHIGAN ALEWIVES IN THE MID-1970S

A bioenergetics model of fish growth was used to estimate phosphorus (P) cycling by the population of Lake Michigan alewives Alosa pseudoharengus in the mid-1970s. The mean annual standing stock of alewives during the mid-1970s contained 1,500 tonnes of phosphorus, representing a substantial pool of particulate phosphorus unavailable to algae. An estimated 12,000 tonnes of phosphorus were egested and excreted annually by the Lake Michigan alewife population. Over half of the alewife-regenerated phosphorus was produced by larvae and age-0 alewives, which inhabit the nearshore epilimnion during summer. Seasonal aggregations of alewives-the dominant component of the Lake Michigan fish community during the mid-1970s-could have served as an important medium of phosphorus regeneration in comparison with more traditionally reported vehicles such as zooplankton. Expressed volumetrically, alewives regenerated 0.22 mug P . L-1 . d-1 during August, which is comparable to phosphorus regeneration rates previously estimated for Lake Michigan zooplankton. Use of a bioenergetics model provided a means to demonstrate that alewives played a substantial role in Lake Michigan phosphorus regeneration during the mid-1970s.