Distribution and Dispersal of the Phyllosoma Larvae of the Western rock Lobster, Panulirus cygnus, in the South-eastern Indian Ocean

Abstract

Data on the phyllosoma larvae of P. cygnus caught on seven cruises carried out between April 1976 and January 1977 off the west coast of Australia are presented and discussed. The studies were undertaken to determine the length of the plankton cycle, the distribution of the phyllosoma in the south-eastern Indian Ocean and the extent of the offshore dispersal.

Analyses showed the average length of the planktonic life to be less than one year and probably between 9 and 11 months. After hatching most early phyllosoma were transported offshore. Few larvae remained on or near the continental shelf. The maximum westward extent of the phyllosoma distribution of P. cygnus was not determined because significant numbers of phyllosoma were still found as far offshore as 99º 001E. (1500 km offshore), the furthest station sampled. The phyllosoma were distributed over an extensive area of the south-eastern Indian Ocean, and there were few stations beyond the continental shelf between 24º 30'S. and 35º 00'S., from 99º 00'E. to 115º 00'E., during midwinter, at which phyllosoma were not caught. The highest densities of mid-and late-stage phyllosoma occurred between 111º 00' E. and 104º 00' E. (between 375 and 1030 km offshore), at 29º 30'S. The area of greatest abundance was due west of the approximate centre of the adult distribution on the coast.

The significance of the circulation of the south-eastern Indian Ocean in the transport of the larvae is discussed.