Effect of Exposure to Ice Slurries on Nonovigerous and Ovigerous Blue Swimmer Crabs, Portunus Pelagicus

Abstract

Commercial fishers of blue swimmer crabs in Western Australia use ice-water slurries to pacify crabs and thereby minimise the damage caused by on-board handling. This study investigated the effect of exposure to ice-water slurries on the mortality and recovery rate of male and female blue swimmer crabs, and on egg loss and the viability of the surviving larvae of ovigerous females. The temperatures (0–158C) and durations (15 seconds to 30 minutes) of exposure in the trials were within the range used by commercial fishers in order to determine the combination of temperature and duration that would pacify the crabs while minimising recovery time. Exposure to ice-water slurries did not kill the crabs except in the most extreme treatments, e.g., 08C for 30 minutes. However, both temperature and exposure time had a significant effect on recovery time, which decreased with increasing temperature. Treatments above 68C had little impact, with crabs recovering instantly, even with 60-second exposure. Exposure to low temperatures did not result in significant egg loss, although females may lose part of their egg mass during on-board handling. Similarly, the effect on the developing larvae was not apparent unless the ovigerous female died. Although exposure of ovigerous and nonovigerous crabs to ice-water slurries had only minimal immediate effects, exposure to 68C for 30 seconds is recommended, as it adequately pacifies crabs for handling and results in a minimum recovery period which may be important in minimising secondary effects.