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

Tagging

Tagging

To obtain data on the growth rate and migration, tagging experiments were begun in June, 1947, and in the following three months 95 specimens were tagged and released. In 1948, an additional 73 were released in June, July, and August page 19 near Moa Point (see Fig. 2). The numbers of specimens released at various points around the coast are indicated in Fig. 2.

Since tags which are attached to the exoskeleton are lost in moulting, special types of tags were used which penetrate the exoskeleton and are embedded in the deeper tissues, and therefore are not so likely to be cast off. These were of two types, 50 of the specimens released in 1947 and all those released in 1948 being tagged with a small arrow-shaped piece of xylonite which was pushed under one of the abdominal terga so that the arrow-head gripped in the dorsal muscle mass, care being taken not to damage the dorsal artery. The shaft, which had a number stamped on it, projected about three-quarters of an inch, and, being white, would be easily seen on recapture. The remaining 45, released in 1947, were tagged with a numbered aluminium disc attached to a short wire whose other end was bent into a hook. The hook end was pushed through a small cut in the ventral aspect Figs. 8-12: Tagging Methods page 20 of the abdomen, turned slightly, and pulled back so that it engaged in the tissues. This latter method has met with success in South Africa, where it has been retained during moulting (Von Bonde, 1928). Von Bonde used aluminium wire, but, as that was unobtainable here, stainless steel was substituted.

One female was recaptured in 1947 (tag No. 3, carapace length 11.5 cm.). This was released on 6th June, 1947, and recaptured on 24th October, and was handed in, in good condition, by the fisherman who caught it. This had been tagged with a xylonite arrow, and the wound contained only a small amount of necrotic tissue. The tag was encased in a chitinous sheath in which a considerable amount of foreign matter was embedded, and this held it firmly (see Fig. 8). Where the tag was in contact with the posterior edge of the tergum, the setae which usually fringe this border were absent, probably as a result of the rubbing action of the tag each time the tail was moved. No change in size had occurred. The crayfish was carrying eggs when released, but these were absent when recaptured, which indicates that hatching occurs between June and October (see page 16), and it had travelled from Ohiro Bay (point B on Fig. 2) to 200 yards off-shore from the fish-oil factory to the west of Island Bay, a distance of about 2,000 yards in four and a half months.

Eight specimens were recaptured in 1948. Two of these were liberated near Moa Point (point I in Fig. 2), the first on 10th July, 1948 (tag No. 125, carapace length 12.9 cm.) and the second on 30th July, 1948 (tag No. 121, carapace length 10.8 cm.). These two had the xylonite tag. Number 125 was recaptured on 15th August, 1948, and No. 121 on 7th September, 1948. Both were males and had travelled from Moa Point to the extremity of the headland to the east of Moa Point, commonly referred to as "the Island" (point C on Fig. 2)—a distance of about 1,300 yards in five weeks.

Fig. 9 is a longitudinal section of the tail of No. 125, There was no sign of necrosis of the tissue surrounding the tag. The tag was surrounded by a small amount of dark-coloured foreign matter. No chitinization could be detected. No change in size or other characters had occurred in either specimen. Number 121 was returned to the water at the same place as soon as it had been examined.

The third specimen (tag No. 91) had been marked with the stainless steel wire tag. It was a male, and was released on 24th August, 1947 and retaken fifty-five weeks later. It was handed in by a Wellington retailer. Unfortunately it had been cooked. The measurements are given below:
Date Total length Breadth Carapace length Weight
24/8/47 21.5 cm. 5.1 cm. 8.2 cm. 255 gm.
15/9/48 23.8 cm. 5.7 cm. 9.1 cm. 319 gm.

The breadth was taken across the carapace in line with the cervical groove. The second set of measurements given above will have been affected by the cooking. page 21 The changes on cooking several specimens of this size have been observed (see page 25), and the measurements given below would be the approximate dimensions of this crayfish before it was cooked:

Length, 23.06 cm.; breadth, 5.7 cm.; carapace length, 9.2 cm.; weight, 370 gm. Fig. 13: Length of Crayfish vs Amount of Meat on Crayfish page 22 The weight of the specimen when it was liberated was taken with a spring balance, but weighing on board a small boat is very inaccurate. Consequently the increase in weight is very approximate. The changes are given below:

Length, 2.1 cm.; breadth, 0.6 cm.; carapace length, 1.0 cm.; weight, 115 gm. It is obvious that the specimen had moulted. Von Bonde (1935, p. 15) found that a specimen, 9.0 cm. in carapace length, kept in an aquarium, moulted twice in one year, whereas one of 10.4 cm. carapace length moulted only once. The tagged specimen was liberated for 55 weeks, so that it is probable that it had moulted twice. This indicates an average increase in size of 0.5 cm. carapace length at each moult.

Since the tag was not observed until the specimen reached the retailer, it is impossible to find the exact locality at which it was caught. Investigations revealed that it was taken by one of two fishermen. One of these was fishing off the Orongorongo River and the other off Island Bay and Palmer Head. The Orongorongo River is about 11,000 yards from the point of release (Palmer Head). Island Bay is about 4,000 yards away. Since another female travelled only 2,700 yards in the same time, it is unlikely that this specimen was retaken at the Orongorongo River. For the same reason, Island Bay is too far away. Accordingly, it is most probable that it was recaptured at Palmer Head, in which case it had either remained there for the whole period of liberation (55 weeks) or had returned to Palmer Head after moving to some other area. This type of tag does not appear to have a very harmful effect on the tissues. A sketch of the tag is given in Fig. 10. The tag lies in a pocket of chitinized tissue. A is an area of partly chitinized tissue surrounded by a denser chitin envelope. B is the main chitinous pocket surrounding the tag. C is the shaft of the tag. D is the part of the pocket, which has not been sectioned. E is the thin exoskeleton of the ventral aspect of the abdomen. Apart from a thin film of necrotic tissue surrounding the pocket, the muscle surrounding the tag seems to be unaffected.

A fourth specimen was recaptured on or about 10th August, 1948, at the same place as Nos. 121 and 125 (point C on Fig. 2). The fisherman who caught it had only recently taken charge of the boat and was unaware of the tagging operations. He returned it to the water without noting the number, so that no data are available from it. The tag was of the xylonite type.

The fifth specimen (tag 44) was tagged with a xylonite arrow and released on 24th August, 1947. It was recaptured 55½ weeks later. The measurements when released and when recaptured are given below:
Date Total length Breadth Carapace length Weight
24/8/47 24.8 cm. 5.8 cm. 9.1 cm. 425 gm.
18/9/48 26.7 cm. 6.0 cm. 9.2 cm. 483 gm.

It was "in berry" when released. When recaptured it had eggs which were near to hatching. These, however, could not be the same eggs. The weight, when page 23 released, is not very accurate, for the reasons described in the discussion of tag No. 91. The changes in dimensions over the period of liberation (55½ weeks) are:

Length, 1.9 cm.; breadth, 0.2 cm.; carapace length, 0.1 cm.; weight. 58 gm. It has obviously moulted. Von Bonde (1935. p. 15) found that a crayfish, 9 cm. in carapace length, moulted twice in one year. Since the tagged specimen was about the same size and was liberated for a year, it is probable that it had moulted twice. The carapace increase is smaller than would be expected from consideration of No. 91 and from comparing it with the increase in total length. This is thought to be due to incorrect measurement of the carapace length when the specimen was liberated. It was released off Palmer Head and recaptured at Moa Point. Consequently, it had travelled 2,700 yards in 55½ weeks.

Fig. 11 shows the tag in position viewed from the posterior aspect to show that the posterior edge of the tergum under which the tag is inserted is bulged outwards, probably as a result of the moulding action of the tag on the soft shell during the hardening process after the moult. The setae which fringe this area arc absent, probably as a result of the tag's rubbing action every time the tail is moved, and this is thought to account for the slight erosion of the shell in this area. Fig. 12 shows the tag in situ in a longitudinal section of the tail. The tag lies loosely in a cavity whose walls are lined with a thick and rather tough chitinous secretion. This pocket narrows behind the head of the tag and is closely applied to the shaft in this region. This constriction prevents the tag from being pulled out and at the same time allows considerable movement of the tag inside the pocket. There was only a thin layer of necrotic tissue surrounding this pocket.

Three specimens were retaken at Moa Point on 16th October, 1948. Two of these, a male (tag 146) and a female (tag 105), after three months' liberty, had moved 300 yards; a male (tag 143), after two and a half months, had moved the same distance. All three were marked with the xylonite tag. None had moulted. The female, "in berry" when released (12th July. 1948), was free of eggs when recaptured. This female and one male (tag 143) were returned to the water again at Moa Point. These nine returns comprise 5.4 per cent. of those released, which is a return of the order usually obtained in tagging work on Crustacea.

It appears that the xylonite tag is not very harmful. It has been retained at the moult in one specimen, and hence may prove to be a satisfactory type for future use. The chitinous sheath probably protects the surrounding tissues from necrosis. The other type of tag is also retained at the moult, and has little effect on the tissues, again probably because of the protection afforded by the secretion of chitin.

Although these two tags have been retained at the moult, it is possible that the chitin secreted around them would be thrown off at a later moult, in which case the tag would be lost.