Optimizing release strategies for red king crab stock enhancement: Effects of release timing

Abstract

Red king crab, Paralithodes camtschaticus, was commercially important around Kodiak, Alaska, USA, in the 1960s and 1970s; however, the stock crashed in the late 1970 s and has remained closed since 1983. The lack of recovery inspired consideration of stock enhancement through the release of hatchery-reared juveniles as a means to bolster the wild population. We examined the effects of release timing on in situ survival of hatchery-reared red king crab by releasing juveniles in June, August, and September 2015 in Trident Basin, Kodiak. We monitored densities inside and outside of release plots for six months using quadrat counts to determine loss and emigration rates. Relative predation risk was determined using tethering experiments performed after each release, and predator densities were quantified using quadrat counts and predator transect counts. Initial mortality over the first 24 h was approximately 53%, and subsequent mortality rates decreased with month-of-release, likely due to a combination of larger size-at-release and seasonal changes in predation. Although predator density was consistent over time, relative predation risk of tethered crabs decreased with season, suggesting later releases may be beneficial. However, the extended hatchery rearing period needed for later releases presents other challenges, including cannibalism, and the potential for developing maladaptive traits. Stock enhancement programs must balance these trade-offs to maximize overall success. Early releases of small juveniles immediately after settlement may be optimal if large-scale hatchery communal rearing results in significant juvenile production loss and/or hatchery conditioning is impractical.