Alternative structural models for the Northeast Chatham Rise orange roughy fishery

Abstract

A particular difficulty with assessments of the Orange Roughy resource on the Northeast Chatham Rise is the seeming inability of standard population models, with their standard assumptions of a linear relationship between CPUE and survey indices to abundance, to simultaneously reflect the trends of all these indices. Especially concerning is that while the outputs from these models suggest a recovery in abundance for the Spawning Box after about 1992, the CPUE and hydroacoustic survey results for that period indicate the reverse. A number of mechanisms have been suggested that might be able to resolve these inconsistencies: resident-and-transient fish (related perhaps to spawning migrations), seasonal patterns, hyperdepletion, disturbance, intermittent aggregation, effort saturation and fishing behaviour (Anon. 2005). The purpose of this paper (following a proposal in Anon. 2005) is to investigate this using a simple age-aggregated population model as a basis.