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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.  Report prepared for the Department of Conservation, Conservation Services Programme. 29 p.