• barriers;
  • drainage;
  • fish passage;
  • irrigation pump;
  • salmonid mortality

Abstract  Hidrostal pumps have been successfully employed in live fish transport, yet their effectiveness in fish passage is incompletely understood. This study investigates juvenile salmonid mortality in experimental passage trials through Hidrostal pumps at an agricultural pump facility in Washington State, USA. The effects of impeller pitch, rotational speed and fish body size on passage survival were examined. Hatchery-reared salmonids [Oncorhynchus mykiss (Walbaum) and Oncorhynchus kisutch (Walbaum)] were introduced to low- and high-pitch impeller assemblies operating at two speeds. Instantaneous mortality rates ranged from 0 to 4% for high-pitch trials and from 3 to 10% for low-pitch trials. Larger fish experienced sublethal injury at higher rates (approximately 60% injured) than smaller fish (approximately 23% injured) and exhibited greater susceptibility to injury at higher pump speed. Injury between trials was compared by ranking according to severity and summed for each treatment; greater injury severity was found for the low-pitch impeller and from higher rotational speeds. Although injury and mortality rates to fish passing through Hidrostal pumps may be reduced through the use of higher-pitch impellers and lower operational speeds, the use of pump-bypass facilities may be warranted where acceptable impact thresholds are low.