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

Maturity of Females

Maturity of Females

Two methods were used in an attempt to find the size at which a female becomes mature. These are:

(i)

Detection of the smallest female "in berry."

Von Bonde (1936, p. 8), working in South Africa, observed females "in berry" page 12 when only 1¾ in. (4.4 cm.) in carapace length. He states that this size is reached at the age of approximately two and a half years. Challenger (1943, p. 52) says: "Very small female fish have been found in Tasmanian waters (1½ in.) with berry attached, which proved, however, to be unfertilized." The measurement of 1½ in. (3.8 cm.) is presumably carapace length. Hickman (1945, p. 31) says: "Of the 572 females examined, the smallest one which, by the presence of empty egg-capsules on the pleopods, gave evidence of having carried eggs, measured 7.2 cm. in carapace length. The smallest specimen actually "in berry" had a carapace length of 7.4 cm. The eggs of this specimen contained embryos at the late nauplius stage of development and therefore had been fertilized."

Of the 1,219 females examined in the present investigation, the smallest one "in berry" was 7 cm. in carapace length (about 19 cm. total length). Of the 12 females smaller than 7.2 cm., none had either eggs or the setae to which eggs are normally attached. These, and a number of others up to 9.7 cm. which had no setae or only a few fine ones, were apparently immature, since the pleopods were not ready for oviposition. The endopodite of the smaller ones was merely a small rod-like projection. In the larger ones (up to 9.7 cm.), it was fully developed, with a few fine setae. It appears that, as the animal grows, the endopodite develops, then setae begin to appear. When these are present in sufficient numbers to form a thick fringe, it is considered that the crayfish is ready, externally at least, for oviposition.

Accordingly, it appears that some crayfish in the Wellington area become mature when a carapace length of 7 cm. is reached, but many do not become mature until they are considerably larger. All appear to be mature by the time they are about 9.7 cm. in carapace length.

The agreement of Hickman's figure and mine for the smallest mature female is to be expected, since the waters of Tasmania and New Zealand have similar temperatures. Challenger's figure suggests the attainment of sexual maturity at a much smaller size. Von Bonde's figure indicates that, in South Africa, where the water is warmer, maturity is reached at a smaller size. This is understandable, since Templeman (1936) found that in the Canadian lobster (Homarus americanus) maturity was attained at a smaller size in warm waters than in cold.

The largest female carrying eggs was 14 cm. in carapace length. The largest female was caught in January, and had setae but no eggs. It was 14.4 cm. in carapace length. This indicates that the largest females caught are still fertile.

(ii)

Detection of change in the growth rate of the abdomen.

Huxley (1932) noted a relationship between sexual maturity and the width of the abdomen in the female Brachyura: "In the female Brachyura the abdomen is always heterogonic in some part of its development, since it is always relatively narrow in the immature stages and relatively broad in the adult." Templeman (1935 and 1944), working on the North American lobster (Homarus americanus), found that the rate of growth of the abdomen began to increase on the attainment page 13 Fig. 5: Analysis of Whole Sample from Catch for 1947 and 1948 page 14 of sexual maturity. A graph of the total length (tip of the rostrum to the end of the telson) against the width of the second segment of the abdomen, expressed as the percentage of the total length, climbed slowly through the sizes up to sexual maturity, when it began to rise more rapidly.

Fig. 6: Sizes of 182 Females

The same method was used in the present investigation to obtain the size at which the female of Jasus lalandii becomes mature. Fig. 6 is a graph of the total length against the abdomen width expressed as the percentage of the total length. The width of the abdomen was taken across the tip of the pleural spines of the first abdominal segment. The curve was fitted by eye. Since there is only a small amount of data on small specimens, it is difficult to get the best fit for the curve in the smaller sizes. There does, however, appear to be a relatively flat region in the graph between 18 cm. and about 19.5 cm. total length. This suggests that sexual maturity is achieved in some females at about 19.5 cm. total length (about 7.2 cm. carapace length), which agrees with the conclusions from the detection of the smallest female "in berry," as described in the previous section.