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INT2024-06 Interaction of spotted shags with northern North Island set net fisheries (PDF, 1,170K)

Summary

This research investigated the degree of spatial and temporal overlap between tracked kawau tikitiki and commercial set net fisheries in the Firth of Thames region. Previously, data of spatially explicit kawau tikitiki diving (foraging) events are available and ready use. Fisheries set net data were obtained from the Ministry for Primary Industries (MPI). We first explored the at-sea behaviour and range of kawau tikitiki, including diving frequency, diving depth and length of dive during the day, and between months. The locations of both kawau tikitiki diving and commercial set net activity were summarised by time of day, month and season, which reflected variation of foraging patterns over different life stages of kawau tikitiki throughout the year. Distinct diving behaviours were observed between male and female individuals and whether the birds foraged in marine farms. Probability density surfaces were calculated from these monthly and seasonal data, and hotspots of kawau tikitiki foraging and fisheries activities were identified. The degree of overlap between kawau tikitiki and fisheries activity-hotspots were estimated to approximate the likelihood of interactions. Fine-scaled behaviour patterns of the kawau tikitiki were assessed, and the spatio-temporal interaction events were also identified. The results of this analysis provided insights into the space-use patterns of kawau tikitiki with seasonal shifts in foraging distribution, including use of mussel farms and a pronounced spring concentration on the Thames coastline. The spatial overlaps between core foraging areas and set net operations were strongest during the spring. The spatial and spatiotemporal overlaps between foraging behaviour and fishing activity presents a conservation concern for this declining, and genetically distinct seabird population, that should be considered for fisheries management, such as restricting fishing areas during spring, and/or limiting fishing hours in the region.

Publication information

Jingjing Zhang, Matt, J. Rayners.05.2025. INT2024-06 Interaction of spotted shags with northern North Island set net fisheries. A Plant & Food Research report prepared for: Department of Conservation, Conservation Services Programme. Milestone No. 6020986. Contract No. 43849. Job code: P/422506/01. PFR SPTS No. 27343.