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A Study of the Marine Spiny Crayfish Jasus lalandii (Milne-Edwards) Including Accounts of Autotomy and Autospasy

Summary

Summary

In 1947 and 1948, 2,126 specimens of Jasus lalandii, caught in Wellington waters, were examined. The data from these show that males range from 17.9 cm. to 48 cm. (total length) and females from 17 cm. to 40 cm. Males and females in Wellington waters reach a greater size than in Tasmania, and males reach a greater size than females in both countries. The size-range of the female population is fairly stable throughout the year, but the size-range of the male population increases temporarily in September.

Females predominate in the December, January, February, and March catches, probably because of moulting in males at that time. In April, few crayfish can be caught, probably because of moulting and egg-extrusion in females and copulation. In May, males predominate, probably because of moulting and egg-extrusion in females. Equal numbers of both sexes are caught in June, July, and August. In September, males predominate, largely as the result of an increase in the number of very large males, and it is at this time that the heaviest catches are taken. After September, the number of females increases, and this sex predominates in December.

The present minimum legal size is reasonable, as it protects most of the immature females, prevents the meat wastage involved in using small crayfish, and affects the fishermen only to the extent of 8% by weight of his catch.

Females become mature between 7 cm. and 9.7 cm. in carapace length. There is no evidence of loss of fertility in old females. Egg-extrusion begins late in April, and all mature females are "in berry" in May. Large females extrude eggs before small ones. Most females release larvae in October, and all females are free of eggs by the end of December. Larval release may be correlated with increasing temperature from August onwards. The number of eggs produced increases approximately as the cube of body length. Females between 8.3 cm. and 13.5 cm. (carapace length) produce 86,000 to 549,000 eggs.

Of 168 specimens tagged and released, nine were recaptured. Two methods of tagging were used, both of which were satisfactory, since the tags were retained in moulting and had little effect on the tissues. A female 24:8 cm. in total length and a male 21.5 cm. in total length page 2 grew 1.9 cm. and 2.1 cm. in total length respectively in one year, during which time two moults would be expected to have occurred. The nine returns indicate no definite migration, merely a random wandering movement.

The amount of usable meat ranges from 47 gm. to 1,449 gm. over the carapace size range 6.7 cm. to 19.6 cm. The weight of usable meat per unit carapace length ranges from 6.7 gm. to 74 gm. over the same size-range. The leg meat in specimens above 9 cm. in carapace length comprises one-third of the total meat. One-half of the crayfish caught are between 9 cm. and 13 cm. in carapace length, and provide one-half of the usable meat in the catch.

A slight shrinkage in the carapace length occurs in cooking, and the total length may undergo a slight increase or decrease. There is a considerable loss in weight, and this increases with size.

Jasus lalandii exhibits autotomy of the legs and autospasy of the antennal flagella. The legs may also exhibit autospasy. The autotomy point in the legs is in the junction of the basipodite and ischiopodite. The autospasy point in the antenna is close to the base of the flagellum. Points for autotomy or autospasy may also exist in the junction of the first and second, and the second and third, segments of the antennal peduncle. Damage to a leg does not always lead to autotomy. Amputation is more common in females than in males, and the total number of legs amputated is also greater in females. In males, all the legs have equal tendencies to be lost, although there is some indication that the fifth leg may be more frequently lost. In females, the tendencies to loss of the first two legs are equal. The third leg is lost three times more often than the first two, the fourth is lost four times as often, and the fifth five times. The frequencies of absence of the first two legs are not significantly different in the two sexes. The frequencies of absence of the third, fourth, and fifth are greater in females than in males. Of the males with leg amputations, 16.2% have more than one leg missing. For females, the corresponding number is 19%. Females in the size-group 28.1 cm. to 30 cm. have the greatest number of amputations. This point is the peak of a normal curve. In males, the curve is not a normal one; the number of amputations increases with size. One or both flagella are sometimes lost in nature and can be regenerated. The loss of a part of a flagellum is thought to be a case where the damage inflicted has not been associated with enough pulling to evoke autospasy. A flagellum may be almost completely regenerated in one year.