Variation in the Amount of Usable Meat

The only parts of a crayfish which are eaten are the tail muscle, which extends into the cephalothorax, and the muscle from the legs and the antennal peduncle.

The legs of small crayfish (up to about 9 cm. in carapace length) are so small that few people would attempt to extract the meat they contain. Accordingly, only the tail meat of these is used. The legs of crayfish larger than about 9 cm. carapace length contain enough meat to make its extraction worthwhile. Consequently, both the leg meat and the tail meat of crayfish larger than 9 cm. is used. For the purpose of this investigation, 9 cm. carapace length was set as an arbitrary minimum for using leg meat. This represents a total length of about 23.5 cm., which is only 0.6 cm. above the legal size-limit.

A number of specimens were measured, "drowned" in tap water to prevent autotomy, brought to the boil in salted water, and boiled for 20 minutes. They were then removed from the water and allowed to cool in the air. This is the procedure followed in the commercial process. When they had cooled, the leg, antennal peduncle, and tail meat was removed and weighed. The meat from the legs and antennal peduncle is hereafter referred to as "leg meat."

It is obvious that the taking of small crayfish involves considerable wastage of potential meat. A specimen of 7 cm. carapace length provides 6.6 gm. per unit carapace length. If crayfish were protected until they had grown to about 9 cm., they would provide 11.7 gm. of usable meat per unit carapace length. At 20 cm., they provide 74 gm. The larger the crayfish, the smaller the waste. This should be taken into consideration in setting a legal size-limit. This should be high enough to prevent the wastage of potential meat. The present size-limit (9 in. total length, i.e., about 9 cm. carapace length) is reasonable in this respect. See page 9.

In Fig. 13 the frequency distribution over the carapace size-range for the whole random sample of the catch for 1947 and 1948 is superimposed on the graph of available meat against carapace length. Since the sample was taken at random, the analysis must approximate the true composition of the whole catch.

Thirty-eight per cent. of the sample falls below the 9 cm. line. The total meat from these crayfish is about 43,000 gm., and is hardly worth taking when compared with the 332,000 gm. available from larger specimens. Under the existing protection, the small, low meat-producing crayfish are able to grow to a more economic page 25 size, and, in addition, are able to reach maturity. The size-group 9 cm. to 13 cm. comprises 50 per cent. of the crayfish caught and provides 52 per cent. of the usable meat.