Studies on southern Australian abalone (genus Haliotis) XI. Movement and natural mortality of juveniles

Abstract The movement and natural mortality of juvenile Haliotis scalaris and Haliotis laevigata aged 1 to 3 years were examined in a grid experiment of the Beinssen-Powell design set up on a boulder slope at West Island, South Australia. The mean rate of movement of H. scalaris was 0.8 m mth-1 and the maximum recorded was 7 m mth-1; the respective rates for H.laevigata were a mean of 0.5 m mth-1 and a maximum of 1.2 m mth-1. Movement of H. scalaris was independent of age and did not vary seasonally. Both species moved directionally east or west, parallel to the shore-line, but there was no significant preference for either direction. Natural mortality plus tag disappearance rate was l.l (s.e. 0.2) for H. scalaris and 1.5 (s.e. 0.3) for H. scalaris and H. laevigata combined; these are equivalent to annual survivals of 34% and 23% respectively. Diver efficiency at finding marked individuals was 0. 70 for H. scalaris and 0.84 for H. scalaris and H. laevigata combined.