The Role of Fishes in the Regulation of Phosphorus Availability in Lakes

Abstract

Several hypotheses concerning the contribution of fishes to nutrient dynamics in lakes were examined. The maximum quantity of excreted phosphorus by fishes was found to be negligible (< 0.33%) when compared to the demand for this element by the seston. Zooplankton (cladocerans and copepods) excretion supplied up to 12% of the daily summer orthophosphate requirements of the seston. The pool of total phosphorus present in the open water fish community was approximately equivalent to that present in the seston while the total phosphorus biomass in zooplankton was only 22 to 40% of that in the seston. Daily incorporation of total phosphorus into fish tissue and losses as fecal phosphorus could constitute up to 40% of total phosphorus in the seston lost due to sedimentation from the epilimnion depending on the feeding habits of the dominant fish species. Nutrient release due to the decomposition of fish carcasses supplied up to 20% of the allochthonous phosphorus entering the south basin in the spring. The prey of the adult fish community is predominantly benthic and littoral in origin. However, the role of predation in structuring benthic and littoral prey populations and its effect on nutrient dynamics is unknown.Key words: budget, excretion, Lake Memphremagog, nutrients, Perca flavescens, yellow perch; phosphorus, population estimate