Catch-rate triggers as a fisheries management tool for short lived species: Can they achieve MEY?

Fisheries based on short lived species are notoriously difficult to manage using traditional effort or catch quota controls. Such fisheries are often characterised by high fecundity, requiring only a small spawning stock to potentially produce a large biomass the following year. This stock, or at least its availability, is driven by unpredictable environmental conditions to a large extent, with the available biomass depleted over the fishing season though both natural and fishing mortality. In most instances, management of these fisheries has focused on ensuring sufficient escapement at the end of the season to allow sufficient recruitment the following year. Catch-rate triggers are one such management tool to determine when fishing should cease. In this study, the use of such triggers in the banana prawn sub-fishery of the Australian Northern Prawn Fishery are assessed. The fishery has an explicit objective of achieving maximum economic yield, and the triggers are set on an economic basis during the season based on price and cost information provided by the industry. The in-season estimates provided by industry were highly correlated with information derived retrospectively through an economic survey, with the industry-provided estimates generally resulting in a more conservative (i.e., higher) break-even catch-rate level. It is the profit maximising behaviour of the fishers, however, that results in the greatest benefits, with most boats leaving the fishery before the trigger catch-rate is reached. The catch-rate trigger operates more as a “safety-net” for the fishery, and possibly a nudge encouraging vessels to maximise their profits given their individual cost structures.