A COMPARISON OF METHODS FOR TAGGING JUVENILE LOBSTERS (HOMARUS-GAMMARUS L) REARED FOR STOCK ENHANCEMENT

The identification of cultured animals on recapture is an integral par t of any modern stock enhancement programme. In lobster (Homarus sp.) release studies this is particularly taxing due to moulting, the small size of juveniles and costs. This work compares five tagging methods with respect to survival and tag retention over three moults. These co nsisted of internally placed tags, i.e., visible implant elastomer and coded microwire tags, two external marks, i.e., rostrum ablation and hot branding, and one external tag, i.e., the polyethylene streamer ta g. A total of 1440 individuals were used in the study. Elastomer, micr otags and rostrum ablations were applied to two age categories, i.e., 1.5 (5-8 mm carapace length (CL)) and 7 month (12-16 mm CL), brands we re given to 7 and 9 month (16-19 mm CL) animals while streamer tags we re given 9 month old individuals only. Older juveniles tagged abdomina lly with microtags and elastomer showed high survival (97%) and tag re tention (99-100%). The younger age class also responded positively to microtags (83% survival and 96% tag retention) but survival was signif icantly reduced to 68%, with obvious tag migration, when this group we re tagged with elastomer. To date, rostrum ablation proved to be a poo r external mark with 100% of juveniles in both age classes successfull y regenerating a rostrum within three moults. Survival of branded juve niles was size specific with levels of 57 and 90% for 7 and 9 month ju veniles, respectively. Visibility of the mark faded with successive mo ults due to repigmentation in the exoskeleton. Lobsters tagged abdomin ally with streamer tags showed high survivorship (99%) and high tag re tention (100%). Occasionally, this tag appeared to interfere with the moulting process and prolonged the time taken to shed the exoskeleton at ecdyses. Based on these findings, implantation of elastomer into ju veniles less than 10 mm CL and branding of individuals less than 15 mm CL is not advised. Branding and ablation are not recommended for long term tagging studies. The internally placed tags, i.e., visible impla nt elastomer and microtags would appear to be more suitable options. ( C) 1998 Elsevier Science B.V. All rights reserved.