The New South Wales Tiger Flathead Neoplatycephalus macrodon (Ogilby). II. The Age Compositon of the Commercial Catch, Overfishing of the Stocks, and Suggested Conservation

Abstract

The commercial flathead catch is analysed into its component age-groups. The results are expressed in numbers and weight of each age-group caught in each month. The results indicate an absence of natural fluctuations in abundance of the year-groups during the series of years covered.

The post-war decline in the catch of flathead is discussed in the light of this analysis. The catch has fallen from 5,700,000 lb. in 1944–45 to 2,100,000 lb. in 1948–49. The catch of flathead for a period between the wars is estimated at over 10,000,000 lb. per year. The stock of flathead has thus shown a failure to recover during the war-time rest, as well as a sudden fall with the inception of heavy fishing of recent years.

Possible reasons for these changes in the flathead stock are discussed. It is suggested that the numbers of recruits are limited by the numbers of spawning adults.

The results obtained from this work are fuller, but in entire agreement with those of the earlier paper on the trawlfishery as a xvliole. The adoption of conservation measures is urged. The trawlfishery is now dependent on two hitherto discarded species of poorer quality than the flathead, and the better of these is already showing a reduced catch per unit effort of fishing. The most important conservation measure is that suggested in the earlier paper — a reduction of the fleet to the equivalent of 13 trawlers. It is regarded as probable that if this step is not taken, the annual trawlfish catch will continue to decline. Closure of the Botany fishing ground is suggested as a further, but not an alternative, measure.