Download AEBR 363 Harbour use by Māui/Hector’s dolphin and commercial net fisheries

Roberts, J. (2025). Harbour use by Māui/Hector’s dolphin and commercial net fisheries. New Zealand Aquatic Environment and Biodiversity Report No. 363. 56 p.

This document provides a summary of existing information of the use of West Coast North Island (WCNI) harbours by Māui/Hector’s dolphins (Cephalorhynchus hectori) and by commercial net fisheries.

Based on this review, Māui/Hector’s dolphins were much more frequently encountered in the coastal domain of the WCNI. By comparison, sightings and acoustic detections in harbour areas were much more infrequent and almost entirely located inside fishing prohibition areas in harbour mouths.

Commercial net fishing effort was described using recent data collected using electronic monitoring, which includes the locations of all reported fishing events. The two main net fishing methods used in WCNI harbours are set-nets and ring-nets, which differ in terms of the gear used and the nature of fishing operations. The overlap of harbour-based set-net effort with the dolphins is likely to be very low. By comparison, the overlap with ring-net fishing with the dolphins is likely to be a little higher in some harbour mouths, although ring-net fishers must attend their gear throughout short deployments, so this method is considered less likely to capture Māui/Hector’s dolphins.

However, several opportunistic sightings of Hector’s and Māui dolphins were made in the summer of 2024/25 that suggest they can move further into harbours and rivers under certain conditions that are not well understood. Therefore, research for understanding the environmental drivers of occasional harbour/river use across the species would be beneficial for understanding when and how often this is most likely to occur and to minimise overlap with fishing.