Trophic state and its implications for natural reproduction of salmonid fish

Abstract

Natural propagation of all fish species native to a particular lake is an ecological requirement of prime importance. Salmonid fish are particularly vulnerable to environmental degradation since egg development takes place on or in the bottom substrate. Dissolved oxygen concentration on the spawning site is commonly considered the main factor limiting egg development. In order to assess the relationship between trophic state, hypolimnetic oxygen concentration, and salmonid egg development, whitefish (Coregonus sp.) eggs were sampled just prior to hatching in late winter. Eggs were collected in 13 Swiss lakes of different trophic state, using a sled-dredge. The proportion of viable eggs among the total number of eggs found was taken as a measure of reproductive success. The results indicate that successful in situ embryogenesis is not primarily governed by hypolimnetic oxygen concentration which tends to be high anyway during egg incubation, but by trophic state in terms of total phosphorus concentration in spring. The findings are explained by the production-related oxygen uptake of the sediment, creating an oxygen gradient of varying steepness in the diffusive boundary layer. Implications for the restoration of lacustrine ecosystems are discussed.