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Comparison of freeze- and heat-branding techniques to mark the coconut crab Birgus latro (Crustacea, Anomura)
.I. Exp. Mar. Biol. Ecol., 1989, Vol. 127, pp. 245-251 Elsevier
245
JEM 01242
Comparison of freeze- and heat-branding techniques to mark the coconut crab Sirgus Zatro (Crustacea, Anomura) W. J. Fletcher i, D. R. Fielder’
and I. W. Brown 3
’ W. A. Marine Research Laboratory, North Beach, Westent Ausealia. Australia; 2Zoology department University of Queensland, St Lucia, Queensland, Australia: 3Fisheries Research Branch. Deception Bay. Queensland, Australia
(Received 2 November 1988; revision received 13 February 1989; accepted 18 February 1989) Abstract: The effectiveness of freeze- and heat-branding as methods to individually identify postmoult coconut crabs Birgus lutro L. was assessed in captive and free-ranging animals. The success of freezebranding was depend~t upon the material used in the branding tool and the length of application. A maximum of 80% success was attained. Heat-br~ding was always successful but the resolution of brands was often poor. The applicability of both branding methods to studies on other crustaceans is discussed.
Key words: Birgus latro; Coconut crab; Crustacean; Cryogenics; Freeze-brand;
Growth; Heat-brand
INTRODUCTION
of the growth rates of crustaceans by direct measurements is to the loss of the exoskeleton on moulting. Consequently, recognition of individuals before and after moulting is not possible using most exoskeletal markers (e.g., paint dots or scratched numbers) because they do not appear on the new exoskeleton. If measurements of growth are made on isolated captive animals, marking of individuals is not necessary but observations on captive animals is difTicult to reconcile with those which occur under natural free-ruing conditions. Anchor tags, which may be retained through a moult, have been used with limited success on lobsters and crabs [see Aiken (1980) and Hartnoli (1982) for reviews] but can only be used on crustaceans which have suitable consolidated muscle masses. Furthermore, they may affect moulting adversely and tagged animals are often interfered with by other conspecifics (Cooper, 1970). An alternative technique to mark individuals through a moulting cycle is by the use of freeze- or heat-bran~ng. The freeze-br~~ng (or cryogenic) method assumes that the rapid freezing and thawing of the epide~~/de~~ layers will destroy chromatophores. Thus, following moulting, the affected area will lack pigment. This technique The
dificult
determination due
Correspondence address: W. J. Fletcher, W. A. Marine Research Laboratory, P.O. Box 20, North Beach, WA 6020. Australia. 0022-0981~89/~03.50 0 1989 Elsevier Science Publishers B.V. (Biomedical Division)
W.J.FLETCHERETAL.
246
has been successfully used on Dungeness crabs Cancer magister (Stroud, 1974) and on a variety of other animals [e.g., snakes (Lewke & Stroud, 1974) and sharks (Jones & Geen) 1976)]. Heat-branding also destroys chromatophores and is often visible prior to moult as the branded exoskeleton turns red. In this paper, we present initial findings on the use of these two methods to mark individual coconut crabs Birgus latro L. (Anomura, Coenobitidae). B. Zatrois the largest land-dwelling crab (occasionally, >4 kg) and, unlike others in this family, it does not house its abdomen in the shell of a gastropod. The abdomen, which is not used in locomotion, has little musculature, making the use of anchor tags inapprop~ate (Amesbury, 1980). Little success has been achieved in getting coconut crabs to grow in captivity, necessitating the development of an appropriate technique by which their growth could be studied under field conditions.
MATERIALS
AND METHODS
Experiments involving the use of a captive group of crabs held in enclosures were carried out in 1986 and 1987. In addition, an extensive field study was carried out from November 1986 to December 1987. ENCLOSURES
1986
10 coconut crabs ranging in size from 14 to 1000 g were collected from the northern region of the island of Espiritu Santo in the Republic of Vanuatu and freeze-branded during the year. The body surfaces considered most suitable for branding were the chitinized tergite plates on their abdomens (Fig. 1). No vital organs are located immediately beneath this area and it was assumed that branding here would cause minimal injury to the crabs. All of these crabs moulted successfully and none died during the experimental period. The coolant used for freeze-branding was liquid freon, Refrigerant 12 {Aerosol Co., Kansas, U.S.A.), which was decanted from a 15kg stock bottle into a smaller l-kg portable gas cylinder to facilitate handling in the field. Coolant was applied using branding tools made from 5 mm thick foam plastic of medium density which was cut into a variety of shapes (bar, dot, X, etc., which were between 50 and 70 mm2 in area) and glued to a backing of plywood with a 15 cm long wire handle. Branding tools were placed into a small plastic jar and sufficient coolant decanted into the jar to saturate the foam. Excess coolant was then shaken from the brand which was immediately placed onto one of nine positions on the crab (three ~sitions on each of the last three tergite plates). The brand was held in place for either 5, 7 or 10 s [following the recommendations of Stroud et al. (unpubl. data)]. The spongy material of the brand conformed to the surface contours of the abdominal tergite. Evaporation of the coolant from the foam results in a supercooling effect. This procedure appeared to induce only minimal discomfort in the crabs, little more than was invoked by general
BRANDING TECHNIQUES TO MARK BIRGUS
LATRO
241
Fig. 1. Photograph of a postmoult crab with good-resolution freeze-brands on its’ abdominal tergal plates. Brands are a “bar” at Position 8 and a “dot” at Position 6.
handling. The area branded initially had the shape of the brand marked by condensation but this quickly evaporated. Crabs were placed into individual enclosures after an identifying number was scratched on their carapace. The enclosures were made from 1 m diameter concrete pipes sunk 0.75 m into the ground and cemented in place to prevent the crabs digging their way out. The tops were covered with marine-grade plywood lids with adequate air holes. The crabs were maintained in these until they moulted. ENCLOSURES
1987
In this series, it was hoped to examine the effect of high-density vs. medium-density foam in the branding tools and different branding times (10 vs. 2 x 10 s) on the effectiveness of freeze-br~~ng. Crabs were also heat-br~ded using distinctively bent 2-mm wire brands welded to metal rods. These brands were heated until they were “red hot”, after which time they were placed onto the crabs’ tergite plates for z 3 s whereupon the normally blue surface of the crabs was burned red. Heat-branding caused a greater reaction from the crabs than that caused by freeze-branding but there was no mortality observed following this treatment.
W. J. FLETCHER ET AL.
248
Nine crabs were marked using a combination of these techniques. Unfortunately, one crab died (after removal of a blood sample) and five crabs broke through the wooden lids of their enclosures and escaped before they had moulted. FIELD EXPERIMENTS
A total of 180 crabs was marked and released at two small island sites (l-3 ha). Some of the crabs marked were originally located on these islands but most were caught elsewhere and released after they had been marked with a scratched number and either a freeze- or a heat-brand.
RESULTS ENCLOSURES
1986
The visibility of brands on the crabs after moulting varied from very distinct (e.g., Fig. 1) to completely absent. Success appeared to be related to the application time and the material used in the branding tools (Table I). Four of the five crabs branded before TABLE I
Details of freeze- and heat-branded crabs that moulted in enclosures. Series 1 crabs were branded between 27 January and 18 March 1986. Series 2 crabs were branded between 1 June and 9 September 1986. Series 3 crabs were branded in 1987. High and low refers to density of foam brands used for freeze-branding. Visibility indices used were: 0, no brand showing; 1, brand present but faint; 2, brand present; 3, brand obvious; 4, damaged exoskeleton/distorted. Series
Branding time (s)
Number of crabs marked
Number with postmoult brands
Mean visibility
1
5 (High) 7 (High) 10 (High) 10 (Low) 10 (Low) 10 (High) 20 (High) Heat
1 2 2 4 3 3 3 2
1 1 2 1 2 2 3 2
1 1 3 0.7 0.6 1.6 2.2 2.0
2 3
June 1986 had visible brands and these were more distinct where the brand had been applied for 10 s. After June, a smaller branding tool was used, which (at a later date) was also found to be constructed of less dense foam. Only one very small crab branded with this tool showed any mark after moulting. ENCLOSURES
1987
Of the three crabs that remained in enclosures through moulting, all had at least one postmoult brand present. Again, the visibility of the freeze-brands seemed related to the
BRANDING TECHNIQUES TO MARK BIRGUS LATRO
249
type of brand used and the duration of application (Table I). Thus, the best result was achieved using the high-density foam applied for 20 s. The heat-branding trials were also successful (Table I). The resultant brands were not, however, as “neat” as the freeze-brands. The edges of branded areas were fuzzy and were often distorted making it difficult to discern the shape of the brand. FIELD
A total of 20 crabs was recaptured in the field with a recognizable postmoult brand. From these marks, we were able to individu~y identify all but one of them. The mean interval between branding and recapture of the postmoult crabs was 9 months for both freeze- and heat-branded individuals (Table II). The average visibility of the brands was TABLE II
Results from crabs captured in field with recognizable postmoult brands. Number
Freeze Heat
Branded
Recaptured
Size of crabs (kg)
112 69
10 9
1.05 0.84
Time at liberty (months)
Mean brand visibility
7” damaged
9.1 9.2
1.8 3.33
0 34
greater for heat-branded crabs but 34% of this group showed some evidence of damage (Table II) and the shape of one brand could not be distin~ished. There was no significant relationship (P > 0.05) between brand visibility and crab size nor with the time interval between branding and recapture. The proportion of recaptured individuals found with postmoult brands vs. those with only scratch marks (premoult) increased during the year but the proportion of recaptured individuals (any mark vs. no mark) did not alter during the year indicating that the branding had a high rate of success. There was no significant difference between the relative success of finding postmoult individu~s with either heat- or freeze-brands (x’ = 0.53; P > 0.05). DISCUSSION
In our study, marking crabs with brands had several advantages over other marking techniques. In this and related investigations, we have found that B&W generally moults only once per year. However, moulting occurs over an extended period (March - October), with individuals often being underground for 2 2 months before they actually moult. Furthermore, given the poor rates of capture at most sites, to mark enough crabs to guarantee a reasonable return, it was necessary to begin branding much earlier than the moulting season. Therefore, it was essential that brands be evident in
250
W. J. FLETCHER ET AL.
crabs which moult 6 months or more after branding (the mean time between marking and recapture was 9 months). In addition, our marking techniques allowed differentshaped brands to be used, enabling a large number of combinations (> 1000) which was necessary for the rates of growth of individuals to be determined. Brands could only be tested on a small number of caged crabs as budgetary and time constraints limited the number of allowable enclosures. Nonetheless, these studies showed that with the correct combination of branding tools and application time, freeze-branding works on a large proportion (80%) of individuals despite the few trials performed. In their more complete (but unpublished) study, Stroud et al. found that out of a number of different coolants and brand materials, Freon 12 and medium-density foam brands gave the best results on Dungeness crabs (70% success). Furthermore, they found that the brands were visible on individu~s after three completed moults following branding. On one small crab kept in our enclosures, the freeze-brand was still visible after two moults but had disappeared after the third. We found that heat-branding was probably more effective in marking individuals (100% success in this study) than freeze-branding but its marks were not as clear as freeze-brands and, unless great care is taken, they can damage the exoskeleton. Similar problems were also encountered by Cooper (1970) who found that the heat-branded area of the carapace of lobsters often eroded after some months. An additions problem was that this technique caused obvious distress to the crabs. The freeze-branding method has already proved invaluable in our study of the growth of B. Iutro and its potential for use on many other species of crustaceans is considerable. This method has worked on two very different species of crustacean and probably only needs to be finely tuned for any target species (i.e., determining brand site and time of application). It is a simple technique which can be applied under field conditions with relative ease and, import~tly, minimal expense. It certainly has advantages over other techniques such as microwire tagging (JefTerts, 1963; ~ontfr~s et al., 1986; Bailey & Dufour, 1987). In addition, individuals may be recognized without killing them and in commercial species there is no danger of people ingesting the tag. Freeze-branding should be, therefore, applicable to most studies of crustacean growth or for any investigation involving long-term mark-recapture techniques. ACKNOWLEDGEMENTS
This study was funded by Australian Centre for International Agricultural Research Project No. 838 1. We would like to thank the Fisheries Department of Vanuatu for their co-operation during the programme and to A. Obed and C. Schiller for assistance. REFERENCES Aiken, D. E., 1980.~oulting and growth. In, The bfolqv and management @lobsters,
& B.F. Phillips, Academic Press, New York, pp. 91-164.
edited
by
J. S. Cobb
BRANDING TECHNIQUES TO MARK BfRGUS LATRO
251
Amesbury, S. S., 1980. Biological studies on the coconut crab (Birgus Intro) in the Mariana Islands. Univ. Guam Tech. Rep., No. 11, pp. 1-39.
Bailey, R.F. J. & R. Dufour, 1987. Field use of an injected ferromagnetic tag on the snow crab (Chionocetes opilio 0. Fab.) J. Cons. Cons. Int. Explor. Mer, Vol. 43, pp. 231-244. Cooper, R. A., 1970. Retention of marks and their effects on growth, behaviour, and migrations of the American lobster, ffomarus ame~canus. Trans. Am. Fish. Se., Vol. 99, pp. 409-417. Hartnoll, R.C., 1982. Growth. In, The biolog? ofcrustacea, Vo!. 2, edited by L. G. Abele, Academic Press. New York, pp. 111-197. J-fferts, K. B., P. K. Bergman & H. F. Fiscus, 1963. A coded microwire identification system for macroorganisms. Nanrre (London), Vol. 98, pp. 460-462. Jones, B.C. & G. H. Geen, 1976. Marking elasmobranchs by freeze branding. Prog. Fish. Cult., Vol. 38, p. 179. Montfrans, J. van, J. Capelli, R. J. Orth & C. H. Ryer, 1986. Use of microwire tags for tagging juvenile blue crabs (Cailinectes sapidus Rathbun). 1. Crustacean Biol. (Woods Hole, Mass.), Vol. 6, pp. 370-376. Stroud, R. K., 1974. Cryogenic marking (freeze branding) of Dungeness crabs (Cancer magister). Aust. Fish., Vol. 33, No. 8, p. 18.
245
JEM 01242
Comparison of freeze- and heat-branding techniques to mark the coconut crab Sirgus Zatro (Crustacea, Anomura) W. J. Fletcher i, D. R. Fielder’
and I. W. Brown 3
’ W. A. Marine Research Laboratory, North Beach, Westent Ausealia. Australia; 2Zoology department University of Queensland, St Lucia, Queensland, Australia: 3Fisheries Research Branch. Deception Bay. Queensland, Australia
(Received 2 November 1988; revision received 13 February 1989; accepted 18 February 1989) Abstract: The effectiveness of freeze- and heat-branding as methods to individually identify postmoult coconut crabs Birgus lutro L. was assessed in captive and free-ranging animals. The success of freezebranding was depend~t upon the material used in the branding tool and the length of application. A maximum of 80% success was attained. Heat-br~ding was always successful but the resolution of brands was often poor. The applicability of both branding methods to studies on other crustaceans is discussed.
Key words: Birgus latro; Coconut crab; Crustacean; Cryogenics; Freeze-brand;
Growth; Heat-brand
INTRODUCTION
of the growth rates of crustaceans by direct measurements is to the loss of the exoskeleton on moulting. Consequently, recognition of individuals before and after moulting is not possible using most exoskeletal markers (e.g., paint dots or scratched numbers) because they do not appear on the new exoskeleton. If measurements of growth are made on isolated captive animals, marking of individuals is not necessary but observations on captive animals is difTicult to reconcile with those which occur under natural free-ruing conditions. Anchor tags, which may be retained through a moult, have been used with limited success on lobsters and crabs [see Aiken (1980) and Hartnoli (1982) for reviews] but can only be used on crustaceans which have suitable consolidated muscle masses. Furthermore, they may affect moulting adversely and tagged animals are often interfered with by other conspecifics (Cooper, 1970). An alternative technique to mark individuals through a moulting cycle is by the use of freeze- or heat-bran~ng. The freeze-br~~ng (or cryogenic) method assumes that the rapid freezing and thawing of the epide~~/de~~ layers will destroy chromatophores. Thus, following moulting, the affected area will lack pigment. This technique The
dificult
determination due
Correspondence address: W. J. Fletcher, W. A. Marine Research Laboratory, P.O. Box 20, North Beach, WA 6020. Australia. 0022-0981~89/~03.50 0 1989 Elsevier Science Publishers B.V. (Biomedical Division)
W.J.FLETCHERETAL.
246
has been successfully used on Dungeness crabs Cancer magister (Stroud, 1974) and on a variety of other animals [e.g., snakes (Lewke & Stroud, 1974) and sharks (Jones & Geen) 1976)]. Heat-branding also destroys chromatophores and is often visible prior to moult as the branded exoskeleton turns red. In this paper, we present initial findings on the use of these two methods to mark individual coconut crabs Birgus latro L. (Anomura, Coenobitidae). B. Zatrois the largest land-dwelling crab (occasionally, >4 kg) and, unlike others in this family, it does not house its abdomen in the shell of a gastropod. The abdomen, which is not used in locomotion, has little musculature, making the use of anchor tags inapprop~ate (Amesbury, 1980). Little success has been achieved in getting coconut crabs to grow in captivity, necessitating the development of an appropriate technique by which their growth could be studied under field conditions.
MATERIALS
AND METHODS
Experiments involving the use of a captive group of crabs held in enclosures were carried out in 1986 and 1987. In addition, an extensive field study was carried out from November 1986 to December 1987. ENCLOSURES
1986
10 coconut crabs ranging in size from 14 to 1000 g were collected from the northern region of the island of Espiritu Santo in the Republic of Vanuatu and freeze-branded during the year. The body surfaces considered most suitable for branding were the chitinized tergite plates on their abdomens (Fig. 1). No vital organs are located immediately beneath this area and it was assumed that branding here would cause minimal injury to the crabs. All of these crabs moulted successfully and none died during the experimental period. The coolant used for freeze-branding was liquid freon, Refrigerant 12 {Aerosol Co., Kansas, U.S.A.), which was decanted from a 15kg stock bottle into a smaller l-kg portable gas cylinder to facilitate handling in the field. Coolant was applied using branding tools made from 5 mm thick foam plastic of medium density which was cut into a variety of shapes (bar, dot, X, etc., which were between 50 and 70 mm2 in area) and glued to a backing of plywood with a 15 cm long wire handle. Branding tools were placed into a small plastic jar and sufficient coolant decanted into the jar to saturate the foam. Excess coolant was then shaken from the brand which was immediately placed onto one of nine positions on the crab (three ~sitions on each of the last three tergite plates). The brand was held in place for either 5, 7 or 10 s [following the recommendations of Stroud et al. (unpubl. data)]. The spongy material of the brand conformed to the surface contours of the abdominal tergite. Evaporation of the coolant from the foam results in a supercooling effect. This procedure appeared to induce only minimal discomfort in the crabs, little more than was invoked by general
BRANDING TECHNIQUES TO MARK BIRGUS
LATRO
241
Fig. 1. Photograph of a postmoult crab with good-resolution freeze-brands on its’ abdominal tergal plates. Brands are a “bar” at Position 8 and a “dot” at Position 6.
handling. The area branded initially had the shape of the brand marked by condensation but this quickly evaporated. Crabs were placed into individual enclosures after an identifying number was scratched on their carapace. The enclosures were made from 1 m diameter concrete pipes sunk 0.75 m into the ground and cemented in place to prevent the crabs digging their way out. The tops were covered with marine-grade plywood lids with adequate air holes. The crabs were maintained in these until they moulted. ENCLOSURES
1987
In this series, it was hoped to examine the effect of high-density vs. medium-density foam in the branding tools and different branding times (10 vs. 2 x 10 s) on the effectiveness of freeze-br~~ng. Crabs were also heat-br~ded using distinctively bent 2-mm wire brands welded to metal rods. These brands were heated until they were “red hot”, after which time they were placed onto the crabs’ tergite plates for z 3 s whereupon the normally blue surface of the crabs was burned red. Heat-branding caused a greater reaction from the crabs than that caused by freeze-branding but there was no mortality observed following this treatment.
W. J. FLETCHER ET AL.
248
Nine crabs were marked using a combination of these techniques. Unfortunately, one crab died (after removal of a blood sample) and five crabs broke through the wooden lids of their enclosures and escaped before they had moulted. FIELD EXPERIMENTS
A total of 180 crabs was marked and released at two small island sites (l-3 ha). Some of the crabs marked were originally located on these islands but most were caught elsewhere and released after they had been marked with a scratched number and either a freeze- or a heat-brand.
RESULTS ENCLOSURES
1986
The visibility of brands on the crabs after moulting varied from very distinct (e.g., Fig. 1) to completely absent. Success appeared to be related to the application time and the material used in the branding tools (Table I). Four of the five crabs branded before TABLE I
Details of freeze- and heat-branded crabs that moulted in enclosures. Series 1 crabs were branded between 27 January and 18 March 1986. Series 2 crabs were branded between 1 June and 9 September 1986. Series 3 crabs were branded in 1987. High and low refers to density of foam brands used for freeze-branding. Visibility indices used were: 0, no brand showing; 1, brand present but faint; 2, brand present; 3, brand obvious; 4, damaged exoskeleton/distorted. Series
Branding time (s)
Number of crabs marked
Number with postmoult brands
Mean visibility
1
5 (High) 7 (High) 10 (High) 10 (Low) 10 (Low) 10 (High) 20 (High) Heat
1 2 2 4 3 3 3 2
1 1 2 1 2 2 3 2
1 1 3 0.7 0.6 1.6 2.2 2.0
2 3
June 1986 had visible brands and these were more distinct where the brand had been applied for 10 s. After June, a smaller branding tool was used, which (at a later date) was also found to be constructed of less dense foam. Only one very small crab branded with this tool showed any mark after moulting. ENCLOSURES
1987
Of the three crabs that remained in enclosures through moulting, all had at least one postmoult brand present. Again, the visibility of the freeze-brands seemed related to the
BRANDING TECHNIQUES TO MARK BIRGUS LATRO
249
type of brand used and the duration of application (Table I). Thus, the best result was achieved using the high-density foam applied for 20 s. The heat-branding trials were also successful (Table I). The resultant brands were not, however, as “neat” as the freeze-brands. The edges of branded areas were fuzzy and were often distorted making it difficult to discern the shape of the brand. FIELD
A total of 20 crabs was recaptured in the field with a recognizable postmoult brand. From these marks, we were able to individu~y identify all but one of them. The mean interval between branding and recapture of the postmoult crabs was 9 months for both freeze- and heat-branded individuals (Table II). The average visibility of the brands was TABLE II
Results from crabs captured in field with recognizable postmoult brands. Number
Freeze Heat
Branded
Recaptured
Size of crabs (kg)
112 69
10 9
1.05 0.84
Time at liberty (months)
Mean brand visibility
7” damaged
9.1 9.2
1.8 3.33
0 34
greater for heat-branded crabs but 34% of this group showed some evidence of damage (Table II) and the shape of one brand could not be distin~ished. There was no significant relationship (P > 0.05) between brand visibility and crab size nor with the time interval between branding and recapture. The proportion of recaptured individuals found with postmoult brands vs. those with only scratch marks (premoult) increased during the year but the proportion of recaptured individuals (any mark vs. no mark) did not alter during the year indicating that the branding had a high rate of success. There was no significant difference between the relative success of finding postmoult individu~s with either heat- or freeze-brands (x’ = 0.53; P > 0.05). DISCUSSION
In our study, marking crabs with brands had several advantages over other marking techniques. In this and related investigations, we have found that B&W generally moults only once per year. However, moulting occurs over an extended period (March - October), with individuals often being underground for 2 2 months before they actually moult. Furthermore, given the poor rates of capture at most sites, to mark enough crabs to guarantee a reasonable return, it was necessary to begin branding much earlier than the moulting season. Therefore, it was essential that brands be evident in
250
W. J. FLETCHER ET AL.
crabs which moult 6 months or more after branding (the mean time between marking and recapture was 9 months). In addition, our marking techniques allowed differentshaped brands to be used, enabling a large number of combinations (> 1000) which was necessary for the rates of growth of individuals to be determined. Brands could only be tested on a small number of caged crabs as budgetary and time constraints limited the number of allowable enclosures. Nonetheless, these studies showed that with the correct combination of branding tools and application time, freeze-branding works on a large proportion (80%) of individuals despite the few trials performed. In their more complete (but unpublished) study, Stroud et al. found that out of a number of different coolants and brand materials, Freon 12 and medium-density foam brands gave the best results on Dungeness crabs (70% success). Furthermore, they found that the brands were visible on individu~s after three completed moults following branding. On one small crab kept in our enclosures, the freeze-brand was still visible after two moults but had disappeared after the third. We found that heat-branding was probably more effective in marking individuals (100% success in this study) than freeze-branding but its marks were not as clear as freeze-brands and, unless great care is taken, they can damage the exoskeleton. Similar problems were also encountered by Cooper (1970) who found that the heat-branded area of the carapace of lobsters often eroded after some months. An additions problem was that this technique caused obvious distress to the crabs. The freeze-branding method has already proved invaluable in our study of the growth of B. Iutro and its potential for use on many other species of crustaceans is considerable. This method has worked on two very different species of crustacean and probably only needs to be finely tuned for any target species (i.e., determining brand site and time of application). It is a simple technique which can be applied under field conditions with relative ease and, import~tly, minimal expense. It certainly has advantages over other techniques such as microwire tagging (JefTerts, 1963; ~ontfr~s et al., 1986; Bailey & Dufour, 1987). In addition, individuals may be recognized without killing them and in commercial species there is no danger of people ingesting the tag. Freeze-branding should be, therefore, applicable to most studies of crustacean growth or for any investigation involving long-term mark-recapture techniques. ACKNOWLEDGEMENTS
This study was funded by Australian Centre for International Agricultural Research Project No. 838 1. We would like to thank the Fisheries Department of Vanuatu for their co-operation during the programme and to A. Obed and C. Schiller for assistance. REFERENCES Aiken, D. E., 1980.~oulting and growth. In, The bfolqv and management @lobsters,
& B.F. Phillips, Academic Press, New York, pp. 91-164.
edited
by
J. S. Cobb
BRANDING TECHNIQUES TO MARK BfRGUS LATRO
251
Amesbury, S. S., 1980. Biological studies on the coconut crab (Birgus Intro) in the Mariana Islands. Univ. Guam Tech. Rep., No. 11, pp. 1-39.
Bailey, R.F. J. & R. Dufour, 1987. Field use of an injected ferromagnetic tag on the snow crab (Chionocetes opilio 0. Fab.) J. Cons. Cons. Int. Explor. Mer, Vol. 43, pp. 231-244. Cooper, R. A., 1970. Retention of marks and their effects on growth, behaviour, and migrations of the American lobster, ffomarus ame~canus. Trans. Am. Fish. Se., Vol. 99, pp. 409-417. Hartnoll, R.C., 1982. Growth. In, The biolog? ofcrustacea, Vo!. 2, edited by L. G. Abele, Academic Press. New York, pp. 111-197. J-fferts, K. B., P. K. Bergman & H. F. Fiscus, 1963. A coded microwire identification system for macroorganisms. Nanrre (London), Vol. 98, pp. 460-462. Jones, B.C. & G. H. Geen, 1976. Marking elasmobranchs by freeze branding. Prog. Fish. Cult., Vol. 38, p. 179. Montfrans, J. van, J. Capelli, R. J. Orth & C. H. Ryer, 1986. Use of microwire tags for tagging juvenile blue crabs (Cailinectes sapidus Rathbun). 1. Crustacean Biol. (Woods Hole, Mass.), Vol. 6, pp. 370-376. Stroud, R. K., 1974. Cryogenic marking (freeze branding) of Dungeness crabs (Cancer magister). Aust. Fish., Vol. 33, No. 8, p. 18.