LONG-TERM CHANGES IN A RESERVOIR FISH ASSEMBLAGE: STABILITY IN AN UNPREDICTABLE ENVIRONMENT

Abstract

Long-term monitoring of reservoir fish assemblages can provide insight into the development, community structure, and stability of economically important fisheries. A sentinel-site approach was used to assess changes in the offshore fish assemblage of a 36 000-ha impoundment (Lake Texoma) across 43 years. Fishes were sampled intensively year-round using gill nets in 1954, 1981–1984, and 1996–1997. Assemblage structure, overall, was relatively stable across years as indicated by persistence of species, significant concordance in rank abundance, relatively low cv of species abundances among years, and overlapping sample scores in multivariate space. However, some individual species varied in abundance across decades. Stepwise discriminant analysis revealed six species that could be used to discriminate collections among decades. A more detailed evaluation of changes in the fish assemblage between the 1980s and the 1990s that included size-structure and species associations showed little variation between decades. However, two species, smallmouth buffalo (Ictiobus bubalus) <400 mm in length and striped bass (Morone saxatilis) <250 mm in length were in greater abundance in the 1990s. Based on this and previous studies, the fish assemblage in Lake Texoma appears to be relatively stable. There is evidence to suggest that populations of introduced species are more susceptible to abiotic disturbances than are native riverine fishes.