Cooperative Fish and Wildlife Research Units Program: Utah
Education, Research and Technical Assistance for Managing Our Natural Resources

Understanding the processes governing population regulation is important for effective conservation and management. Disentangling the relative role of density-dependent versus density-independent population regulation is often made difficult by the inability to control for abiotic or biotic factors, but long-term datasets are invaluable in this pursuit. We used a 14-year dataset from the Logan River, Utah to assess long-term trends in abundance and evidence of density-dependent and density-independent population regulation of Paiute sculpin (Cottus beldingii) across six sites. Additionally, we evaluated the feeding ecology of sculpin over four years. Sculpin densities generally increased from downstream to upstream, and the per capita rate of increase was negatively and significantly correlated with sculpin density at four of six sites. We also observed a negative relationship between per capita consumption and sculpin density, providing a potential mechanism for density-dependent population regulation. Sculpin displayed a generalist feeding strategy, and interannual differences in diet composition appeared to be influenced by interannual differences in flow, particularly years with higher magnitude flow. The observed spatial patterns in sculpin abundance throughout the watershed matched those of invasive brown trout (Salmo trutta), which are the top piscivore in the Logan River. Our results suggest sculpin populations are regulated largely by density-dependent processes and match those from other studies on sculpin population dynamics including a range of species and habitats that differ vastly in abiotic conditions.