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 part 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 consisted 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 tag. A total of 1440 individuals were used in the study. Elastomer, microtags 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 were given to 7 and 9 month (16–19 mm CL) animals while streamer tags were given 9 month old individuals only. Older juveniles tagged abdominally with microtags and elastomer showed high survival (97%) and tag retention (99–100%). The younger age class also responded positively to microtags (83% survival and 96% tag retention) but survival was significantly reduced to 68%, with obvious tag migration, when this group were tagged with elastomer. To date, rostrum ablation proved to be a poor external mark with 100% of juveniles in both age classes successfully regenerating a rostrum within three moults. Survival of branded juveniles was size specific with levels of 57 and 90% for 7 and 9 month juveniles, respectively. Visibility of the mark faded with successive moults due to repigmentation in the exoskeleton. Lobsters tagged abdominally with streamer tags showed high survivorship (99%) and high tag retention (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 juveniles 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 implant elastomer and microtags would appear to be more suitable options.