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 μg 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 mid1970s.