FAR 2025/33 Characterisation and spatio-temporal CPUE standardisation of school shark in the NZ EEZ

Mormede, S.; Dunn, A. (2025). Characterisation and spatio-temporal CPUE standardisation of school shark in the NZ EEZ. New Zealand Fisheries Assessment Report 2025/33. 67 p.

This study on school shark analysed catch and effort data from 2008 to 2024, using commercial fishing data from three main fishing methods (set nets, bottom trawls, and bottom longlines) to estimate changes in relative abundance at several spatial scales.

The key findings were:

• school shark should be treated as one connected population throughout New Zealand waters;
• school shark numbers appear stable over recent years at about the level of the target reference period (2012–2018);
• school sharks move extensively around New Zealand waters. They were more common on the Chatham Rise and west coast of New Zealand in 2012–2014, but shifted toward the east coast in 2022–2024;
• the fishery has evolved from being mainly set nets (60% of catch in 1990) to a more balanced fishery of set nets, bottom trawls and longlines (about 30–40% each by 2024);
• the spatio-temporal modelling method provides more consistent population estimates than previous techniques, and lets us estimate CPUE indices for the population as whole, as well as regional and CPUE indices as required for management; 
• the approach helps resolve conflicts between the CPUE indices estimated from different fishing methods and in different areas that have previously showed contradictory trends.

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