Populations of Barracouta, Thyrsites atun (Euphrasen), in Australian Waters.

Abstract

Different populations of barracouta (Scombriformes: Acinaceidae), the principal Australian fish of commerce, have been recognized by a study of differences in the following: spawning season; size composition of adult stock; and seasonal movements and annual fluctuations as revealed by records of catch and fishing effort. Tagging experiments gave little information because of the low rate of commercial exploitation of the populations. There are probably five populations in southern coastal waters, which make migrations to certain areas as follows: one in winter and spring to eastern Victoria and southern New South Wales, one from spring to autumn to Bass Strait and its western approaches, one in summer and autumn to eastern Tasmania, one in autumn and winter to South Australia and western Victoria, and one (possibly not distinct from the previous population) in autumn and winter to the south coast of Western Australia. Spawning and feeding take place in the course of these migrations. Little is known about the populations when they are not migrating, but the three first-mentioned groups all appear to seek the neighbourhood of eastern Bass Strait between the migratory seasons. The fish prefer waters of about 13-180C and tend to vacate areas when they become cooler or warmer than this. Only the Bass Strait and eastern Tasmanian populations are significantly fished and the size of the catches is generally governed by the demand. However, there have been occasional years of scarcity, such as 1950-51 and 1951-52 in Bass Strait and 1951-52 in eastern Tasmania. These represent natural fluctuations (there is no evidence of depletion of any population) and for the Bass Strait population they are probably fluctuations in availability in the fishing areas rather than in abundance of the whole population. It is considered that the combined Australian populations could yield 10 times as much as the present annual catch of 6,000,000 Ib (beheaded and cleaned) when fluctuations were not adverse.