A modelled cost-benefit analysis of hybrid PIT and conventional tagging scenarios

Abstract

Tag recovery rate is an important parameter for estimating exploitation and natural mortality in fshed populations. Passive integrated transponder (PIT) technology can record 100% of PIT tagged animals passing within the detection limit of a PIT tag scanner. However PIT tags and PIT tag scanners are expensive compared with conventional visual tags and PIT tags are not detectable without scanners. We used simulation to evaluate the hybrid PIT tag which has the PIT tag incorporated into a conventional tag allowing both electronic detection capability by a scanner and visual detection by fshers. Simulated estimates of the precision and accuracy of exploitation and natural death rates for two lobster fshery management regimes: a 7-month season for both sexes and a fshery with a 10- and 6-month season for males and females, respectively, were used to determine the benefit of PIT tags. For a project budget of AUS$200,000, hybrid PIT tags and 10% of the feet being equipped with scanners produced more precise and accurate estimates of exploitation rate and natural death rate until tag reporting rate by fshers exceeds 40% for the two-gender management regime and 90% for the 7-month combined sex regime. Increasing the number of scanners to 20% of the feet resulted in fewer hybrid PIT tags being inserted for the same cost and did not improve the precision or accuracy of estimates. Increasing the number of lobsters tagged by tagging during a higher catch rate period improved the precision of exploitation and natural death rate estimates at lower tag reporting rates for the conventional tag scenario, but did not alter the tag reporting rate required to make conventional tagging more benefcial than hybrid PIT tagging. Increased tag reporting rate by the 90% of the feet that were not equipped with scanners had no signifcant impact on the precision or accuracy of estimates for either management regime. © The Royal Society of New Zealand 2009.