Site Fidelity and Movement of Hatchery-Reared Lingcod In Puget Sound

Lingcod (Ophiodon elongatus) are highly-sought targets of recreational fishermen in Puget Sound, Washington, USA.  Lingcod population declines have prompted strong fishing restrictions.  The release of hatchery-reared lingcod may be a viable means to bolster the wild population, but development of a stock enhancement program requires a cautious approach that includes releasing small numbers of fish and monitoring their impacts on natural lingcod and other imperiled species.

In the future, a Before-After-Control-Impact (BACI) experimental design will quantify the potential costs and benefits of lingcod stock enhancement.  To determine the impacts on wild fishes, the abundance and diversity of wild fishes will be monitored at two impact sites where hatchery-reared lingcod are released, and compared to two control sites where no hatchery lingcod are present.  However the BACI experiment would be compromised if released lingcod disperse away from impact sites or to control sites. 

In preparation for the future BACI experiment, we learned about the site fidelity and movement behavior of hatchery-reared lingcod by releasing telemetry-tagged individuals at different ages, seasons, and habitats.  A tag-effects study indicated that the telemetry tags do not affect movement behavior, provided that the fish are allowed sufficient time to recover after tagging.  Telemetry tracking was conducted to quantify site fidelity and movements away from the release site.  The poorest site fidelity was observed in the two youngest release groups (approximately 9 and 11 months post-hatch).  Approximately one year after release, 2% of these two subyearling release groups were detected within three-km of the release site while 17% were detected further away.  Seventeen-month-old lingcod that were released in the summer showed the best site fidelity, with 23% remaining within three-km of the release site one year after release.  Thus, this release age and season may be best suited for the future BACI experiment.  We will describe movement patterns to provide some insights into the behavioral mechanisms that may cause subyearling and yearling lingcod to differ in distributions one year after release.  Hatchery lingcod behavior will also be compared to published studies on wild lingcod behavior.