Long-term changes in a reservoir fish assemblage: Stability in an unpredictable environment

Long-term monitoring of reservoir fish assemblages can provide insight into the development, community structure, and stability of economically import ant fisheries. A sentinel-site approach was used to assess changes in the o ffshore 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 sta ble across years as indicated by persistence of species, significant concor dance in rank abundance, relatively low cv of species abundances among year s, and overlapping sample scores in multivariate space. However, some indiv idual species varied in abundance across decades. Stepwise discriminant ana lysis revealed six species that could be used to discriminate collections a mong decades. A more detailed evaluation of changes in the fish assemblage between the 1980s and the 1990s that included size-structure and species as sociations showed little variation between decades. However, two species, s mall-mouth buffalo (Ictiobus bubalus) <400 mm in length and striped bass (M orone saxatilis) <250 mm in length were in greater abundance in the 1990s. Based on this and previous studies, the fish assemblage in Lake Texoma appe ars to be relatively stable. There is evidence to suggest: that populations of introduced species are more susceptible to abiotic disturbances than ar e native riverine fishes.