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

Number of Eggs Carried by Females of Various Sizes

Number of Eggs Carried by Females of Various Sizes

Hickman (1945) counted the number of eggs in 2-gram samples from six specimens, and obtained an average of 8,520 (standard error 93). He used this average to obtain the total number of eggs on specimens of various sizes by multiplying this number by the total weight of eggs on a specimen and dividing by 2.

This work has been repeated in the following manner: The whole egg-mass was stripped from the pleopods and weighed. Two grams of the mass was weighed out. The eggs, which are attached to one another by tough fibres so that the mass consists of a series of connected compact bunches, were separated from one another by hand, using a scalpel and forceps. After separation, the eggs were counted in an apparatus described by Bradstock (1948). Ten two-gram samples were counted, giving a mean of 7,630, with standard error 275. This mean is comparable with Hickman's, although the variation is greater. Using this mean, it was found that the number of eggs carried by 28 crayfish between 8.3 cm. and 13.5 cm. in carapace length ranged from 86,000 to 549,000. Hickman found that, for a range in carapace length from 7.4 cm. to 12.4 cm., the number of eggs ranged from 65,170 to 413,220. Von Bonde and Marchand (1935, p. 11) state that the number of eggs carried "may vary, according to the female's size, from about 3,000 to nearly 200,000." In a later publication, Von Bonde (1936, p. 9) says that this number varies from "about 3,000 in the smallest to about 20,000 in the largest. page 18 Hickman quotes these figures without comment, but, since Von Bonde gives no explanation of why he changed the upper limit from 200,000 to 20,000, it seems that the 20,000 may be a misprint. Challenger (1943, p. 52) reports that an "average specimen carried 850,000 eggs." This so-called "average specimen" was 5 in. (12.7 cm.) in carapace length. This is actually a very large female. His figure is 547,000 higher than mine for a specimen only 0.2 cm. smaller and 450,410 higher than the figure obtained by Hickman for a specimen 0.3 cm. smaller. The difference between Challenger's figure and those of other workers, combined with the fact that he does not describe his method in any detail, leaves the accuracy of his method in doubt.

Herrick (1895, p. 52), discussing the American lobster (Homarus americanus), gives the general law of fecundity. "The number of eggs produced by female lobsters at each reproductive period vary in geometrical series, while the lengths of the lobsters producing these eggs vary in an arithmetical series." The figures given above indicate that this applies also to Jasus lalandii. Hickman found that his data obeyed this law with considerably less variation than the data presented here. Lateste (1896) observed that the number of eggs carried by a female lobster should be proportional to the volume of the body or cube of the length—i.e,
ifE is the number of eggs laid, and
L is the length of the female, and
K is a constant, then
E = KL2

This is another way of expressing Herrick's law, whence K = E over L-cubed

Von Bonde (1936) found that, for 50 specimens of Jasus lalandii in South Africa, the value of K varied between 263 and 265, so that this law is obeyed. For 28 specimens in the Wellington area ranging from 8.3 cm. to 13.5 cm. in carapace length, the value of K ranged from 135 to 261, with the mean value 194 (standard error 7.2). This indicates considerable variation, but there is, however, a tendency to constancy, so that the law is, at least approximately, obeyed. It is to be noted that the value of K is lower in Wellington than it is in South Africa. This means that the number of eggs produced increases with length more quickly in South Africa than in Wellington.