Hotspots and drivers of seabird–fisheries interaction risk in dynamic seascapes

Ho Fung Wong

doi:10.25907/01116

Humans have long relied on marine resources, with fisheries representing one of the most widespread maritime industries globally. Pelagic longline fisheries, in particular, contribute substantially to the incidental capture (bycatch) of non-target marine wildlife, including cetaceans, sea turtles, and seabirds. Among these, albatrosses, shearwaters, and large petrels are especially vulnerable, with bycatch recognised as a major driver of population decline. This conservation issue occurs across regional, national, and international jurisdictions, posing a persistent challenge for effective mitigation. To address this problem, I quantified seabird–fisheries overlap using a standardised framework that integrates satellite-tracking data describing fine-scale movements of individuals at sea with high-resolution data describing the distribution of longline fishing activity. I first applied this framework to a single-species case study of the Antipodean albatross, examining variation in overlap across life stages and temporal scales. I then expanded this approach from a regional focus to a global analysis, producing a large-scale estimation of seabird–longline overlap across multiple species, accounting for population size. To better understand the environmental drivers of overlap, I incorporated seascape features into the analyses. In Chapter 2, I included a suite of static and dynamic oceanographic variables, as well as three mesoscale features (thermal front frequency, finite-size Lyapunov exponents, and eddy kinetic energy). Subsequently, in Chapter 4, we examined the influence of thermal front characteristics (frequency, strength, and persistence) on global overlap hotspots. In Chapter 2, overlap for the Antipodean albatross with pelagic longline fisheries was concentrated in the Tasman Sea (25°S–40°S) and varied strongly across life stages and seasons, with juveniles experiencing the highest exposure. The likelihood of overlap was elevated in regions of frequent thermal fronts at seasonal scales, while overlap magnitude was further amplified at finer temporal scales in association with Lagrangian Coherent Structures, indicating a role of dynamic aggregation processes. In Chapter 3, four major global hotspots of overlap for albatrosses, Procellaria petrels and shearwaters were identified: (i) the Agulhas Current, (ii) the Tasman Sea, (iii) the North Pacific, and (iv) the Patagonian shelf break. These hotspots were predominantly located in Areas Beyond National Jurisdiction. Overlap varied across species assemblages and seasons, demonstrating that overlap is structured not only geographically but also by temporal dynamics and population-specific exposure. In Chapter 4, thermal-front frequency and strength consistently increased the probability of seabird–fisheries co-occurrence across ocean basins (odds ratios > 1), indicating that frequent and strong frontal zones are commonly targeted by both seabirds and fishing activity. However, their influence on the magnitude of overlap was weaker and less consistent, suggesting that while fronts structure where overlap is likely to occur, finer-scale processes govern the magnitude of overlap. Together, these findings shift the focus from mapping overlap to understanding the processes that structure it. They demonstrate that seabird–fishery overlap emerges from the combined influence of environmental structure, species ecology, and fisheries behaviour, with mesoscale features playing a key role in structuring exposure. This provides a foundation for more targeted and adaptive mitigation strategies. For example, elevated overlap between 25°S and 30°S in the western–central Pacific highlights the need for improved mitigation coverage for juvenile and female Antipodean albatrosses. More broadly, the concentration of global overlap hotspots in the High Seas and their association with dynamic ocean features underscores the importance of strengthened cross-jurisdictional management. Integrating environmental indicators into exposure assessments offers a pathway toward more responsive, spatially explicit approaches to bycatch mitigation for threatened, endangered and protected species.

Hotspots and drivers of seabird–fisheries interaction risk in dynamic seascapes

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