Management strategies for short-lived species: The case of Australia's Northern Prawn Fishery: 1. Accounting for multiple species, spatial structure and implementation uncertainty when evaluating risk

Abstract

The Northern Prawn Fishery harvests a variety of prawn species including some short-lived species with highly variable recruitment such as banana prawns and slightly longer-lived tiger prawns with less variable recruitment. An evaluation of stock assessment methods and management strategies for the Northern Prawn Fishery using the management strategy evaluation (MSE) approach requires an (operating) model of the resource to act as the ‘truth’ for the analyses. A five-stock, two tiger prawn species operating model with a weekly time-step is developed and conditioned using more than 30 years of logbook catch and effort data as well as the results of fishery-independent research. The operating model is projected beyond the present using stock-specific stock–recruitment relationships. Banana prawns are not modelled explicitly, but their impact on the management system is simulated empirically. The input control nature of the management system is mimicked using an effort allocation model that allocates effort by species, area and week. This model allows for the impact of changes over time in efficiency, a key uncertainty in the assessment of these species, and the impact of management implementation error, which has historically been substantial. Some of the properties of the operating model are illustrated by projections based on a constant effort policy.