MORTALITY AND TAG LOSS IN DART AND LOOP-TAGGED CAPTIVE SNAPPER, PAGRUS-AURATUS (SPARIDAE), WITH COMPARISONS TO RELATIVE RECAPTURE RATES FROM A FIELD-STUDY

Tag shedding rates of Hallprint dart and loop tags, and tag-related mo rtality in the snapper Pagrus auratus were experimentally determined o n fish held in captivity for periods up to 18 months. An artefact of t he experimental process appeared to exacerbate dart tag shedding in on e treatment. However, for other treatments, the instantaneous shedding rates for the first 7 months was 0.0006 day(-1). Shedding rates were not linear for periods beyond 7 months and were described by a logisti c function. The instantaneous shedding rate for the loop tags was much lower at 0.00016 day(-1). Overall mortality during the experiment was only 1.9% and the causes of death could not be related to tagging. Th e relative return rates of the two different tag-types from a field ta gging programme were compared after analysis of fish size, spatial, te mporal, and tagger-type distribution. In all direct comparisons within each stratum, loop tag return rates were higher. It was concluded tha t the retention capabilities are better for loop tags than for dart ta gs in P. auratus.