A Perspective on Great Lakes Fish Community Rehabilitation

Abstract

Review of the ASPY syntheses suggested that destabilization and subsequent fish community recovery in the Great Lakes are compatible with a model in which postglacial succession, and the structure and persistence of the fish communities, were governed by piscivores. Recent advances in the areas of particle size distribution, ontogenetic niche theory, and ecosystem stability contributed to a broader understanding of fishery management alternatives. Species succession in Great Lakes aquatic communities is characterized as a cyclic repetition of maturation followed by seasonal, annual, or periodic setbacks. These are termed "enjuvenation events" and are attributed to any cultural or climatic factors which induce flux in energy–matter delivery to the system. The extent of enjuvenation is dependent upon the magnitude of the perturbation and maturity of the community and is predictable to some degree by the age and biomass distributions of the species present. The time course of rehabilitation to any arbitrary prior condition of the community is closely related to the enjuvenation–maturation cycle and to the life span and reproductive characteristics of the species present. The principal homeostatic mechanism is perceived to lie with variations in the durations of life history stanzas as affected by fish growth rates. The "biomass storage" function of larger organisms in the system is thought to be a major determinant of the "biotic inertia" or sensitivity of the community to perturbations. We are convinced that trophic linkages from the piscivores downwards must be maintained as biological feedback pathways to ensure that moderately excessive fishery yields can be self-limiting. Without these linkages (vulnerable to intensive exploitation or other catastrophic reductions in predators), biomass capture of nutrient inputs by algae will vector to waste as planktivore density limits secondary production. The extent to which the fish community can be maintained or driven to a particular species composition is dependent upon the degree of external control of all sorts that can be applied to the system. The rehabilitation continuum ranges from a self-sustaining assemblage of native species requiring little external control to a completely artificially supported community of non-native species requiring extensive controls for both water quality and fish community maintenance.