Movements and associated observations of bait-attracted White Sharks, Carcharodon carcharias: A preliminary report

Abstract

Basic population parameters and behaviours of great white sharks, Carcharodon carcharias, were studied during four expeditions to Spencer Gulf, South Australia. In all, 58 white sharks were observed, ranging in length from about 2.2 to 5.5 m TL (X= 3.7 m TL ± 0.7 s.d.); of these sharks, 32 were subsequently tagged. Many sharks were observed repeatedly, the most frequently resighted individual being seen on 22 days over a 197-day period spanning two expeditions. Sharks in the study area were segregated by sex but not by size. Females were most abundant at 'inshore' islands, whereas males occurred mainly at 'offshore' islands. Further, there were no marked differences in abundance between summer and winter.

Nine ultrasonic trackings, lasting a maximum of 27.5 h, revealed three general horizontal movement patterns: downstream circling, island patrolling, and inter-island cruising. Average rate of movement was 3.2 km h^-1 (n = 145 time intervals of 15 min each). Sharks generally remained near the surface or along the bottom (about 20 m), spending relatively little time in midwater. Daytime swimming depths were significantly shallower than those at night.