An Integrated Multistock Multiarea Assessment Model for New Zealand Snapper (Chrysophrys auratus) Incorporating Home Fidelity Movement

A spatially disaggregated stock assessment model was developed to assess New Zealand’s largest snapper (Chrysophrys auratus) stock management complex (SNA 1). This model, which utilises length and age, CPUE and tagging data from multiple fisheries across three areas and three stocks, ranks as one of New Zealand’s most structurally complex stock assessment models. The model uses a home fidelity (HF) dynamic to model stock movement between three spatial areas. Under the HF dynamic, movement is an attribute of the individual fish not the area in which it currently resides; stocks and areas can therefore be decoupled such that during some of the model time steps a given area may contain fish from one or more stocks. The HF decoupling property meant the model could provide yield estimates (MSY, BMYS, B0, etc) relative to both stocks and areas. The results from the SNA 1 assessment provide some insight into challenges associated with incorporating greater complexity into fisheries assessments; a likely requirement under an Ecosystem Approach to Fisheries (EAF).