The Tasmanian Whitebait, Lovettia seali (Johnston), and the Whitebait Fishery

Abstract

The biology of the aplochitonid Lovettia seali (Johnston), which comprises over 95 per cent. of the Tasmanian whitebait catch, has been studied. Over 78,000 fish from 95 samples were sexed and measured, and 1,200 were classified as to maturity, pigmentation stages, and the presence or absence of food in the stomach. Vertebra counts were made for 1,200 specimens, and there were other observations upon smaller amounts of material. There are marked resemblances to other salmonoids in most points of the biology. There is conspicuous sexual dimorphism. The fish are anadromous and at their ascent are all mature or almost so, and all of the same age (one year by otoliths). After spawning begins there is progressive discoloration and emaciation, followed almost invariably by death. About 0.001 per cent. of the stock consists of two-year fish. The eggs are large compared with the size of fish (extremes of standard length in the adult stock are 33 and 70 mm.) and the incubation period is about three weeks. The larvae drift downstream to the sea. Sex ratio is highly variable, but generally the males greatly outnumber the females. A northern and a southern population can be distinguished, the differences being in growth rate and pigmentation. Each population supports a separate fishery, which operates on the ascending shoals. The history of the fisheries is outlined. The southern fishery has never been important because the fish available at the principal fishing locality are excessively pigmented. More suitable fish could be taken by operating further downstream, where the fish are typically at an earlier stage of maturity. The northern fishery has been vigorously prosecuted and overfishing was probably the cause of the decline in abundance of stock in 1947 and 1948. If there was overfishing, it operated purely by excessive removal of reproducers. The order of the optimum catch is empirically identified and a programme for the management of the stock, aiming at its rehabilitation, is recommended.