AbstractMicrotagging is an adequate method of ensuring correct recapture estimates in enhancement of natural lobster,Homarus gammarus(L.), stocks through releases of cultured juveniles. This paper compares three lobster size categories (8‐10, 12‐14 and 16‐18 mm), two tag lengths (0.5 and 1.0 mm), and two methods of holding the animal during marking with respect to tag retention and survival. A total of 1721 individuals were used in the experiment. The results did not reveal any obvious trends in tag retention related to either different tag lengths or different lobster sizes. Lobster held laterally during tagging showed higher tag retention (94‐99) than lobsters held with the ventral side uppermost (74‐97). Examination, using X‐ray, of 81 juveniles which had tested negative for the presence of tag by the magnetic sensing device, showed that four of these in fact had tags. This suggests that the true tag retention figure could be higher than shown in the results. The cumulative mortality ranged from 0 to 4.7 after 3 days, but only for the smallest animals marked with 1 ‐mm tags laterally: this was significantly higher than in the control group. After 20 days, the cumulative mortality ranged from 0 to 5.7. but there were no significant differences between experimental and c
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