Effect of a baited trap on the foraging movements of juvenile western rock lobsters, Panulirus cygnus George

Abstract

The influence of a commercial trap on the foraging movements of juvenile P. cygnus was determined by tracking animals to which electromagnetic tags had been attached. Catch rates were low. Tagged lobsters were caught on eight occasions; on 14 occasions, tagged lobsters visited the trap and stayed for several hours during the night, but left by morning. The greatest distance travelled by a lobster from down stream to the baited trap was 120 m. On 19 occasions lobsters upcurrent from the trap passed as close as 20 m without going to the trap, although other lobsters as far away as 75 m upcurrent visited the trap. Previous tracking records of individuals foraging upcurrent of the trap suggest that these lobsters' visits may have been due to the trap's location within their foraging range rather than to detection of the bait.

Present trapping techniques used to estimate the densities of juvenile lobsters on individual patch reefs may be biased because lobsters on neighbouring reefs as far away as 120 m could be attracted to the baited trap. The present results also suggest that some lobsters may leave the traps before sunrise, and that traps set closer than 120 m apart may fish competitively for the same individuals.