A laboratory study of the effect of streamer tags on mortality, growth, moulting and duration of nocturnal emergence of the tiger prawn Penaeus esculentus (Haswell)

Abstract

Under laboratory conditions, negligible mortality occurred in Penaeus esculentus larger than 24 mm carapace length (C.L.) when tagged with 2-mm wide streamer tags. About 2% of prawns smaller than 19 mm C.L. tagged with 1.5-mm tags died each week during a 10-week experiment. This was significantly more than in controls. Tagged prawns had a shortened intermoult period and a reduced size increment at each moult, but overall growth of all sizes tested was not affected by streamer tags. The presence of a tag did not alter the time of night at which ecdysis occurred nor the duration of ecdysis, although tagged prawns required significantly more flicking movements to remove the abdominal exuviae than did control prawns. Newly trawled but untagged prawns had a severely reduced duration of nocturnal emergence, but under laboratory conditions this effect disappeared after 14 days. Prawns held in the laboratory for 14 days and then tagged showed a reduction in the duration of nocturnal emergence for the first 5 days after tagging. Newly tagged prawns exposed to light do not bury in the substrate as rapidly as control prawns, and thus may be vulnerable to predation if released near dawn or in daylight.