Resilience of pink salmon and chum salmon to simulated fisheries capture stress incurred upon arrival at spawning grounds

We compared exhaustion-related physiological stress and physical injury as contributors to fish condition, longevity, and egg retention in two Pacific salmon species after their arrival at spawning areas. Adult female Pink Salmon Oncorhynchus gorbuscha and Chum Salmon O. keta were exposed to six experimental capture treatments that represented different levels of exhaustive exercise, air exposure, and injury. After we evaluated its reflex impairment and obtained a blood sample, each fish was released into its natal spawning channel with an external tag and later retrieved postmortem to evaluate spawning success via examining egg retention. Reflex impairment, plasma lactate, chloride, potassium, and osmolality varied among treatments, with differences generally driven by the length of exposure to capture stress, which included exhaustive exercise and air exposure. However, overall prespawn mortality was negligible (about 5%) and consistent across treatments for both species. We hypothesize that Pink and Chum Salmon are resilient to capture-related exhaustion upon reaching spawning areas because of a combination of low water temperature (about 12°C in this study) and a physiological shift towards increased use of anaerobic pathways during their final weeks of life. The capture and release of fish arriving at the spawning ground does not appear to influence survival, in contradiction to the results of other studies, which focused on earlier components of Pacific salmon spawning migrations. Fisheries adjacent to spawning sites represent the end of the continuum of salmon fisheries that begin with the high seas fishery and extend through the coastal and riverine environments. The mortality rates in this study should be interpreted cautiously by management until research efforts are broadened to provide a better understanding of how postrelease outcomes at different life stages compare in natural systems and under conditions more representative of real fisheries.