Growth of imperiled bluehead sucker under anthropogenically-altered temperature and flow regimes

Over-allocated water due to diversions and dams alters the natural flow and temperature regime in river systems which in turn affects fish reproduction, growth, and survival often lead to fish population declines. Bluehead sucker (Catostomus discobolus), native to the Weber River, Utah, currently face an apparent “recruitment bottleneck” likely due to changes in the contemporary hydrologic regime. Our goal was to compare growth of bluehead sucker from three different reaches of the Weber River with distinct thermal and hydrologic regimes. We aged a minimum of 12 bluehead sucker pectoral fin rays from each reach and measured the distance between annuli to determine annual growth of each fish. The warmer reach had both a higher average temperature and mean discharge over the 13 years of observation versus the two cooler reaches. We observed that fish from the warmest reach (average July temperature: 20.0 °C) generally grew faster than fish from two cooler reaches (average July temperature: 17.4°C; influenced by discharge from dams). Mature age-6 fish from the warmer section averaged 440 mm whereas fish from the two cooler reaches averaged 412 mm. Our findings can contribute to the conservation of this bluehead sucker subpopulation by providing a better understanding of their optimal thermal and hydrologic habitat requirements, to help guide habitat restoration efforts