Ecological fish production in Long Pond, a lakeshore lagoon on Long Point, Lake Erie

Synopsis

Long Pond, a recently formed 2.4 ha lagoon on Long Point, Lake Erie (Canada), was treated with piscicide and found to contain 47,768 fishes of 22 species. Nine dominant species (Notropis heterolepis, Pimephales notatus, Notemigonus crysoleucas, Lepomis gibbosus, L. macrochirus, Perca flavescens, Cyprinus carpio, Micropeterus salmoides and Carassius auratus) comprised 91% and 97% of total numbers and standing crop respectively. Age, growth and production were determined giving a total fish production estimate (corrected for all species) of 87.5 kg ha⁻¹ y⁻¹ for this lagoon. Dominant species were deemed either invaders (Cyprinus carpio, Carassius auratus), which had entered the lagoon to spawn and been trapped, or residents. The invaders comprised 82% of the 277.8 kg ha⁻¹ total standing crop. Their successful spawning and subsequent escape of the young from the lagoon would have resulted in some 615 kg y⁻¹ of fish production outside the lagoon. Resident stocks were dominated by young fishes, a characteristic of exploitation or early colonization. This may have been due to the recent formation and subsequent expansion of the lagoon or high annual mortality due to extreme physical conditions but was most likely the result of excessive predation by Micropterus salmoides. Relationship between biomass and production show that the chance inclusion of the invaders produces an immediate shift from a characteristically early to a characteristically late phase of ecological development.