Cannibalism in red king crab, Paralithodes camtschaticus (Tilesius, 1815): Effects of habitat type and predator density on predator functional response

Red king crab, Paralithodes camtschaticus, an important fishery species in Alaska, exhibits cannibalism both within and among age classes. Cannibalism in crab species can be an important determinant of recruitment success, and this might be especially important in king crab because year-0 and year-1 crab occupy the same habitat types in the wild. In this study we used laboratory experiments to determine the predator functional response, or the effect of prey density on predation rates of year-1 crab preying on year-0 crab in three different habitat types: Sand, which was unstructured soft sediment, Whole Shell, which was whole clam valves, and Shell Hash, which was smaller pieces of crushed shell. We also examined how predator density (one or two predators) affects the functional response. The data was fit to Type I, or density independent, Type II, or inversely density dependent, and Type III, or density dependent, functional response models and the best fit model was chosen using Akaike's information criterion. The functional response was a Type II in all habitat types; however, the predation rate was lower at all prey densities in the Whole Shell habitat than in Shell Hash and Sand. The functional response was a Type II at both predator densities as well. The presence of a second predator decreased both the attack rate and the handling time, resulting in slightly lower predation rates at low prey densities, and slightly higher predation rates at high prey densities when compared to the single predator treatment. This indicates a low level of predator interference. This work has implications for potential stock enhancement activities, as year-1 crab could inhibit enhancement success though cannibalism of introduced year-0 crab, especially given the destabilizing nature of the Type II functional response. A potential solution would be to enhance a given area only every other year to give previous cohorts a chance to start podding in less complex habitats. Future work should examine whether the presence of alternative prey changes the functional response to a Type III, as this would give year-0 crabs a low‐density refuge from predation.

► Red king crab exhibit cannibalism between and among age classes.
► We determined the cannibalistic functional response of year-1 crab on year-0 crab.
► We examined the effects of habitat and predator density on the functional response.
► The function response was type II in all habitats and at all predator densities.
► Predation was lower in complex habitats and predators exhibited minor interference.