Effects of release procedures on the primary stress response and post‐release survival and growth of hatchery‐reared spotted seatrout Cynoscion nebulosus

Abstract

To help explain the apparent poor post-release success of hatchery-reared (HR) spotted seatrout Cynoscion nebulosus, this study examined the effects of handling, transport and release procedures on the stress response of two age classes [48 and 80 day post-hatch (dph)] of HR C. nebulosus, as measured by cortisol concentrations and the post-release survival and growth of 48 and 80 dph HR C. nebulosus. As a proxy for stress, tissue cortisol was measured at various times during the handling, tagging (80 dph), transport, acclimation and release process. To consider the implications of the pre-release stressors, growth and survival were monitored in separate field experiments for each age class of acclimated post-transport C. nebulosus using control C. nebulosus that only experienced anaesthesia, transport, acclimation and a net release v. experimental C. nebulosus that underwent the entire routine procedure, including anaesthesia, tagging, transport, acclimation and gravity release through a pipe. For 48 dph C. nebulosus, mean cortisol varied significantly throughout handling and transport, increasing more than six-fold from controls before decreasing in mean concentration just prior to release. For 80 dph C. nebulosus, cortisol varied throughout handling, tagging and transport, first increasing more than three-fold compared with control C. nebulosus, before decreasing and rising slightly just prior to release. For 48 dph C. nebulosus within field enclosures, survival was high and similar for control and experimental groups; experimental C. nebulosus, however, were shorter, lighter and lower in condition than control C. nebulosus. For 80 dph C. nebulosus within field enclosures, fewer experimental C. nebulosus survived and those that did survive were of lower condition than C. nebulosus from the control group. Small untagged C. nebulosus may survive the release procedure better than larger C. nebulosus carrying a coded-wire tag. These findings document some ways in which pre-release practices may translate into detrimental effects on post-release success of HR C. nebulosus.