Abstract. - A laboratory study 

 showed that when small male snow 

 crabs are tagged with the anchor of 

 a t-bar tag inserted into the dorsal 

 musculature, tag retention and sur- 

 vival through the first molt are ex- 

 cellent; when the tag anchor is situ- 

 ated in the basal leg musculature, 

 animals die while molting. When re- 

 captures were obtained from larger, 

 field-tagged animals, it was noted 

 that some animals which had molted 

 had been tagged in the leg muscula- 

 ture. Dissections were performed on 

 43 animals which molted and 89 ani- 

 mals which did not molt to determine 

 tag anchor placement. Four general 

 locations were noted: dorsal muscu- 

 lature, basal leg musculature, loose 

 in the body cavity, and attached in- 

 ternally to carapace. Relative tag 

 retention/survival associated with 

 molting was estimated for the differ- 

 ent tag anchor locations by compar- 

 ing the proportions of tags in each 

 location among animals which molted 

 and among those which did not. Ani- 

 mals with anchors in the leg muscu- 

 lature appeared to survive and retain 

 the tag through a molt as well as 

 those tagged in the dorsal muscula- 

 ture and those with the tag attached 

 to the inside of the carapace. Ani- 

 mals with anchors loose in the body 

 cavity appeared to have worse tag 

 retention/survival than those tagged 

 in the dorsal musculature. The hy- 

 pothesis that tag placement does not 

 affect retention/survival through 

 molt was tested by fitting hierarch- 

 ical loglinear models and testing for 

 a significant interaction between 

 molt status (i.e., did or did not molt) 

 and tag anchor location. No statis- 

 tically significant effect was found, 

 but it still seems prudent to try to 

 place tag anchors into the dorsal 

 musculature. 



Effect of Tag Anchor Location on 

 Retention/Survival through Molt in 

 Male Snow Crabs Chionoecetes opilio 



David M. Taylor 

 John M. Hoenig 



Science Branch, Department of Fisheries and Oceans 



P.O. Box 5667. St. John's, Newfoundland A1C 5X1, Canada 



Manuscript accepted 4 December 1990. 

 Fishery Bulletin, U.S. 89:325-329 (1991). 



A tagging study was initiated in Con- 

 ception Bay, Newfoundland, Canada, 

 to determine the growth in size of 

 male snow crabs Chionoecetes opilio 

 at the time of molting. The t-bar tag 

 (Floy Tag Mfg. Co., Inc., Seattle, WA 

 98105) was selected because prelim- 

 inary studies had shown that the tag 

 can be retained through a molt 

 (McBride 1982, Taylor 1982). Early 

 tag return rates were lower than ex- 

 pected, so a study was initiated to 

 evaluate the performance of the tag 

 when applied to animals held in cap- 

 tivity (Hurley et al. 1990). The lab- 

 oratory study, conducted on animals 

 ranging in size from 60 to 83 mm 

 CW (carapace width), demonstrated 

 that survival and retention of tags 

 through a molt was excellent, pro- 

 vided the tag anchor was inserted 

 into the dorsal musculature (Fig. 1). 

 However, when the tag anchor was 

 inserted into the basal leg muscula- 

 ture, the animals died during the 

 molt. Tissue necrosis associated with 

 Pseudomonas sp. bacteria was fre- 

 quently noted around the tag anchor 

 regardless of where it was located in 

 the body. 



For the Conception Bay study, an 

 effort was made to carefully insert 

 the tag anchors into the dorsal mus- 

 culature. It was therefore surprising 

 when some animals that had molted 

 were recaptured with the anchor in 

 the basal leg musculature. Also, some 

 crabs had tags with the anchor loose 

 in the body cavity, while in others it 

 was attached to the carapace. Since 

 the animals examined in the field 



study were larger (82-120 mm CW at 

 tagging) than the ones used in the 

 laboratory study, it was hypothesized 

 that placement of the tag anchor may 

 not be as critical for large animals as 

 for smaller ones. 



In this paper, we present the re- 

 sults of dissecting 132 recaptured 

 animals to determine location of the 

 tag anchor within the body. We de- 

 velop analytical procedures to esti- 

 mate the relative rate of tag retention 

 and survival at the time of molting 

 for different anchor locations. We 

 test the hypothesis that retention/ 

 survival is the same for all locations 

 using hierarchical loglinear models. 



Materials and methods 



Male snow crabs were tagged in Con- 

 ception Bay during 1983 and 1984 

 using methods described by Hurley 

 et al. (1990) and Taylor and Hoenig 

 (1990). The t-bar tag consists of a 

 vinyl anchor 8 mm long, 1.2 mm in 

 diameter, attached perpendicularly 

 to a 25mm-long shaft, 0.5mm in 

 diameter, which in turn connects to 

 a 50-mm length of Number 20 vinyl 

 tubing printed with identificaion infor- 

 mation. Tags were inserted through 

 the posterior ecdysial suture (epim- 

 eral line) which was made visible by 

 applying gentle upward pressure to 

 the carapace. The location of tag in- 

 sertion was on the right side of the 

 body 2-6 mm from the coxopodite of 

 the last walking leg (Fig. 1). Before 

 releasing the crab, the end of the tag 



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