Further Results of Tagging Sea Mullet, Mugil cephalus Linnaeus, on the Eastern Australia Coast

Abstract

An account is given of tagging operations in eastern Australian waters on sea mullet. The operations involved fish of wide age and size ranges in a variety of habitats and localities, in all months of the year except July. The recoveries from these operations are analysed for information on movement, growth, and mortality. The results show the movement of the tagged fish to be predominantly northwards and require a postulate that southward movement takes place among the young fish (and possibly eggs). The movement of individual fish can be quite rapid and cover long distances, and each fish probably migrates a number of times during its lifetime. The proportion of the population involved in these movements probably exceeds 50 per cent. The results show that there is on the coast one continuous stock of this species, of which the populations occupying the numerous rivers and lakes constantly intermingle. Confirmation was obtained of the earlier workeon the technique of scale reading in this species, and of the general results on average growth rate. Growth occurs chiefly in summer, but possibly also in the latter part of spring and the early part of autumn. The physiology of scale growth and trhe formation of annual "breaks" are discussed. Proportional recoveries from each operation are reported but these cannot serve well a s an index of intensity of fishing. On the other hand, the longevity of the tags serves to indicate the probable life expectancy of these groups of fish; this is estimated as slightly more than 3 yr.