How does stocking density affect enhancement success for hatchery-reared red king crab?

Abstract

Stock enhancement of red king crab (Paralithodes camtschaticus (Tilesius, 1815)) could increase the crab population near Kodiak, Alaska, which collapsed in the 1980s and has not recovered. We conducted a field experiment examining the effect of juvenile red king crab density on enhancement success. Hatchery-reared crabs were released in plots near Kodiak at three densities: 25, 50, and 75 m−2. Crab densities were monitored for 6 months after release. Predation risk was measured via tethering experiments and predator density via quadrat and transect surveys. Neither migration nor mortality changed with crab density, but mortality rates decreased over time. Crab density did not affect predator density or predation risk, although predation risk decreased with time. Excluding the high initial mortality rate of 67.5%, the predicted survival after 6 months was 34%, which is better than the survival observed in a wild population. This suggests that red king crab enhancement is not predation limited and can occur at high densities. Further, processes affecting juvenile red king crab may not be strongly density dependent, at least at the scales and habitats tested.