Comprehensive evaluation of passive tags show no adverse effects in an economically important crustacean

Abstract

Animal tagging can reveal important information about population size, growth and survivorship, however the accuracy of this information relies on establishing that tags are retained and that there are no adverse tag-associated effects. A suite of potential effects associated with Coded Wire Tags (CWTs) was investigated in captive and in wild Nephrops norvegicus. The study included a total of 232N. norvegicus (107 tagged and 125 untagged) which were held captive in the laboratory over 12 months. No tag loss was recorded in these captive N. norvegicus despite moulting having occurred in 77/107 tagged individuals. Recovery of tags from the initial tagging site or otherwise was compared in captive and wild animals by tagging and releasing an additional 205N. norvegicus into Clew Bay, Co. Mayo in Ireland, and recapturing them approximately one year later. Tag movement away for the site of injection consistently occurred in ∼23% of cases (all treatments combined). In ∼10% of individuals, tags were found at the individual’s extremities and, due to their precarious position, these tags would certainly have been lost during the next moult. However, tag movement was very consistent across groups organized by sex (male/female), mobility (captive/wild) and growth increment (high/low), therefore the proportion of tags lost during longer experiments is not predicted to be biased across these groupings. Mortality was not increased in tagged individuals relative to controls in large (above median) or small (below median) size classes in either males or females. In fact, mortality was reduced in tagged females of both sizes compared with the untagged group. An apparently positive effect of tags was that the frequency of moulting was higher in tagged males and females compared with their untagged counterparts. Differences in growth increment at moult were also seen in males, with tagged individuals growing up to 50% more. While the latter was conceivably a sampling artifact, the beneficial effect of tags on moulting warrants further study. Overall, the results indicate no negative effects of CWTs on N. norvegicus growth and survival.