Invasive red king crabs feed on both spawned-out capelin and their eggs

ABSTRACT: The aim of the present study was to test the hypothesis that the invasive red king crab Paralithodes camtschaticus may hamper capelin (Mallotus villosus) recruitment through egg consumption. Field studies (2005, 2006), laboratory experiments (2011), and models of consumption were applied. To explore the response of the predator to prey density, crab abundance and capelin egg density were estimated in stratified study areas. Stomach evacuation rates of capelin eggs in red king crab stomachs were investigated experimentally, and the average evacuation time estimated to be 5.38 h at 2.9°C. The average evacuation time was applied to a consumption model where uncertainty in input values was assessed by Monte Carlo simulation. Estimated egg consumption values were 0.04% and 2.23% of the total number of eggs in studied spawning areas, in 2005 and 2006, respectively. The high variability in quantity of eggs in stomachs generated most of the uncertainty in consumption estimates. Red king crabs did not show an aggregative response to capelin egg density, nor was the magnitude of egg consumption correlated with egg density. Dead post-spawn capelin was a major and more important prey than eggs for red king crab. Our findings imply that semelparity in Barents Sea capelin may lead to predator swamping, thereby reducing capelin egg consumption by the invasive red king crab.