No abstract

The June sucker Chasmistes liorus is an endangered adfluvial fish species that is endemic to the Utah Lake basin. This species remains endangered due to a lack of recruitment. Anthropogenic changes to June sucker lotic and lentic habitat has likely led to recruitment failure. Changes to Utah Lake include increased water temperature, increased turbidity, and eutrophic and saline conditions. The remaining spawning habitat for June suckers in the Provo River has experienced flow, temperature, and channelization modifications. We tested the hypothesis that recruitment failure is caused by a thermal shock that occurs when larvae are transported in the drift out of the Provo River (12-198C) and into Utah Lake (17-258C). We used two laboratory methods-direct transfer and acclimated chronic exposure (ACE)-to determine (1) the upper lethal temperature (ULT) and (2) the acute and chronic mortality associated with larval exposure to an acute thermal shock. The ULT of larvae acclimated to 168C was 338C. Survival varied from 81% to 95% for larvae that were directly transferred from 168C (acclimation temperature) to 19-298C and held for 7 d; survival was not significantly different from that of the 168C control. A modified ACE method was used to mimic the riverto-lake transition. Acclimation temperatures of 12, 16, and 198C were increased by 5-88C over 4-6 h. After approximately 30 d, survival ranged from 42% (transition from 168C to 218C) to 87% (transition from 198C to 278C). Mean weight of fish that received the 19-278C transition treatment was significantly greater than that of all other treatment groups except the 19-258C transition group. Warmer incubation and rearing temperatures led to increased growth and survival. We conclude that thermal shock does not explain June sucker larval recruitment failure in Utah Lake, and we suggest that other factors are responsible for the recruitment failure.