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INT2024-08 Westland petrel overlap with domestic fishing effort (PDF, 2,984K).

Summary

Seabird bycatch in fisheries is a major conservation concern globally, yet fine-scale evaluations of overlap, and thus, indirectly, risk, remain limited for many species. Tāiko/Westland petrel (Procellaria westlandica) are endemic to Aotearoa (New Zealand) and exclusively breed at a single colony near Punakaiki on the West Coast of Te Waipounamu (South Island). This species is highly vulnerable to bycatch in domestic fisheries, including surface longline, bottom longline, and trawl fisheries. To quantify tāiko distribution and overlap with domestic fishing effort, we combined four consecutive years of broad-scale adult geolocation (GLS) tracking data (2021-2025; n = 146) with two years of fine-scale GPS tracking (2024-25; n = 37). We applied two complementary analyses: (i) raster-based overlap, aggregating GLS tracking and fishing data into gridded surfaces to evaluate co-occurrence intensity across space and time, and (ii) point-based spatiotemporal overlap, measuring direct coincidence between individual bird GPS locations and E-logbook recorded fishing events.

We then contrasted these approaches with recorded bycatch events (n = 120; 2020-2025). GLS data revealed strong seasonal connectivity between Aotearoa and South America. However, surprisingly, tāiko occurred in Aotearoa waters year-round. Consequently, broad-scale raster-based analyses indicated year-round overlap with domestic fisheries, peaking austral mid-winter in core breeding areas and dominated by deepwater trawl, particularly for hoki (Macruronus novaezelandiea), followed by deepwater ling (Genypterus blacodes) bottom longline fisheries. Fine-scale point-based analyses showed incubating birds spent an average of 2.1 hours per day within 3 km of fishing vessels, with >98% of co-occurrence time near trawlers. Contrasting with these co-occurrence patterns, recorded bycatch predominantly originated from deepwater ling bottom longline fisheries (despite high observer coverage in multiple fleets). Our findings underscore that co-occurrence does not always directly translate to bycatch risk and that fleet specific catchabilities should be considered alongside other fishery- or fleet-specific nuances. More importantly, our results highlight the current level of tāiko bycatch within the ling bottom longline fishery and thus further targeted efforts to reduce bycatch of this endemic species in this fishery is required.

Additionally, the deepwater trawl fishery would benefit from improved data collection, particularly to quantify warp strike risks, to place the current high co occurrence with low recorded bycatch into the necessary context. Our approach combining multiple data sources thus provided robust insights to guide evidence-based bycatch reduction strategies, without the direct need to employ highly complicated modelling exercises.

Publication information

Waipoua, T., Rutter, J., Simister, K., Bose, S., Taylor, G., Rowley, O., Debski, I., Fischer, J. 2026. Westland petrel overlap with domestic fishing effort. Conservation Services Programme, Department of Conservation, Wellington, Aotearoa New Zealand. 29 p.