Mortality of juvenile brown shrimp Penaeus aztecus associated with streamer tags.
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Immature brown shrimp were marked with plastic streamer tags, then observed in large tanks for the effect of tags on mortality under a variety of pre- and post-tagging treatment regimes. Except where tagged animals were held at low density (9 animals/m2) and with few untagged conspecifics (2/m2), mortality was about 50% higher among tagged animals than among untagged controls. Differences among treatment groups in the number of handling steps, the wound caused by the tagging needle, the duration of high-density holding prior to release, and the sex of test animals were independent of mortality. The identity of the tagger and the size and condition of animals selected for tags were associated with small differences in survival in certain trials. Evidence from direct observation and from damage to tags suggested that mortality was higher among tagged animals because tags evoked attacks from untagged conspecifics and (in one trial) fish. In light of contrary evidence from some earlier studies, the clearer water and greater holding density in our study may have promoted tag-induced mortality by increasing the probability of interactions among animals.