Loss of tags, double-tagging and release methods for eastern king prawns, Penaeus plebejus (HESS): laboratory and field experiments

Abstract

Experiments were done in the laboratory and in the wild to determine the best procedure for tagging eastern king prawns in estuaries in New South Wales, Australia. At the end of an 88-day experiment in the laboratory, there were no significant differences in mortality among prawns tagged with wide (2 mm wide) or narrow (1.5 mm wide) streamer tags, and untagged (control) prawns. Loss of tags was far greater for narrow (70%) than wide (38%) tags because of greater shedding of tags (38 and 2%, respectively). Mean mortality of untagged prawns at the end of the experiment was 13%. Estimates of instantaneous rates (week −1) of tag-induced mortality and shedding of tags combined were derived using an exponential decay model were 0.056 (± 0.01) and 0.039 (± 0.014) for narrow and wide tags, respectively. The instantaneous rate of mortality for untagged prawns was 0.011 (± 0.008) week −1. Growth of prawns that survived to the end of the experiment was unaffected by tagging or the size of the tag. Survival of tagged prawns in the wild did not differ between those released on the surface or bottom, nor between prawns released one or two nights before harvesting. It also did not differ between single- and double-tagged prawns. No double-tagged prawns shed tags. This pattern was the same as that for single-tagged prawns in the laboratory experiment. Streamer tags 42 mm long and 2 mm wide should be used to tag eastern king prawns longer than 20 mm C.L. (carapace length). In waters no deeper than 7 m, tagged prawns can be released on the surface and exposed to harvesting as early as one night after being released. It is also recommended that double-tagging be considered as a viable method for investigating mortality and shedding of tags among penaeids.