A Study of the Marine Spiny Crayfish Jasus lalandii (Milne-Edwards)

Abstract

Jasua lalandii occurs in South Africa, the southern coasts of Australia, Tasmania, New Zealand, Chile, Juan Fernandez, Tristan da Cunha, Saint Paul (Indian Ocean). In South Africa, Australia and New Zealand it is of considerable economic importance. In South Africa a valuable canning industry has existed since 1902. In 1938-39 this produced £129,862 worth of canned 'crawfish'. The value of the exports of frozen tails and canned meat was £243,010 in 1939. In Australia and New Zealand large numbers are cooked and sold on the local market. In New Zealand, in 1946, 16,766 hundredweight (£30,801) of crayfish was marketed. The value of canned and frozen crayfish exported was £11,704. The landings at Wellington were greater than at any other port (£7,685) but Dunedin exported overseas a greater amount of canned and frozen crayfish (£5,314) than Wellington (£4,938). Jasus lalandii has been extensively studied in South Africa, chiefly by Gilchrist (1913-1920), Gilchrist and C. Von Bonde (1922), C. Von Bonde (1928), W. Von Bonde (1930), C. Von Bonde and Marchand (1935 a and b) and C. Von Bonde (1936). Some work has been carried out in Australia by Challenger (1943) and Sheard (1947), in Tasmania Hickman (1944 and 1945). In New Zealand, Parker (1884) described the skeleton and Young (1926) studied the growth of a crayfish in captivity. Apart from this, no work appears to have been done in New Zealand. Whenever natural resources are tapped it is essential that a sound method of utilization be adopted. Too often has a population of an animal of economic importance been exploited beyond the economic limit. Before a proper method of utilization can be evolved, it is necessary to have a thorough knowledge of the natural history of the species concerned. This is moderately well known for crayfish in South Africa but little is known of the species in New Zealand. This thesis is an attempt to increase our knowledge of the crayfish in New Zealand waters. The work has been restricted to the Wellington area from Oteronga Bay to the Orongorongo River (see figure 2). The fishing is carried out mainly in shallow water around the rocky parts of the coast. Observations were made during 1947 and 1948 on board the fishing boats operating from Island Bay. These boats supply most of the crayfish consumed on the Wellington Market and some of the catch is sent to inland towns in the Wellington province. Random samples of the catch have been examined as often as has been possible. On each occasion, weather conditions, temperature and, in the earlier part of the study, salinity have been noted. These observations have given data on the population composition and its variation throughout the year, the onset and duration of the spawning season, the effect of minimum size restrictions on the fisherman's income, segregation of the sexes and migration, and the onset of maturity in females. In 1948, special fishing was carried out at Moa Point using a dinghy and pots similar to those used by the fishermen. This work has provided additional data for the studies mentioned above and, in addition, it has provided specimens for laboratory work on fecundity of females of various sizes, estimation of the glycogen content of the meat, estimation of the amount of usable meat in specimens of various sizes and shrinkage in cooking.