Fine‐scale interactions between boats and large albatrosses indicate variable susceptibility to bycatch risk according to species and populations

Use of bird-borne radar to examine shearwater interactions with legal and illegal fisheries

Seabirds interact with fishing vessels to consume fishing discards and baits, sometimes resulting in incidental capture (bycatch) and the death of the bird, which has clear conservation implications. To understand seabird-fishery interactions at large spatiotemporal scales, researchers are increasing their use of simultaneous seabird and fishing vessel tracking. However, vessel tracking data can contain gaps due to technical problems, illicit manipulation, or lack of adoption of tracking monitoring systems. These gaps might lead to underestimating the fishing effort and bycatch rates and jeopardize the effectiveness of marine conservation. We deployed bird-borne radar detector tags capable of recording radar signals from vessels. We placed tags on 88 shearwaters (Calonectris diomedea, Calonectris borealis, and Calonectris edwardsii) that forage in the northwestern Mediterranean Sea and the Canary Current Large Marine Ecosystem. We modeled vessel radar detections registered by the tags in relation to gridded automatic identification system (AIS) vessel tracking data to examine the spatiotemporal dynamics of seabird-vessel interactions and identify unreported fishing activity areas. Our models showed a moderate fit (area under the curve >0.7) to vessel tracking data, indicating a strong association of shearwaters to fishing vessels in major fishing grounds. Although in high-marine-traffic regions, radar detections were also driven by nonfishing vessels. The tags registered the presence of potential unregulated and unreported fishing vessels in West African waters, where merchant shipping is unusual but fishing activity is intense. Overall, bird-borne radar detectors showed areas and periods when the association of seabirds with legal and illegal fishing vessels was high. Bird-borne radar detectors could improve the focus of conservation efforts.

Albatrosses develop attraction to fishing vessels during immaturity but avoid them at old age

Animals have to develop novel behaviours to adapt to anthropogenic activities or environmental changes. Fishing vessels constitute a recent feature that attracts albatrosses in large numbers. While they provide a valuable food source through offal and bait, they cause mortalities through bycatch, such that selection on vessel attraction will depend on the cost-benefit balance. We examine whether attraction to fishing and other vessels changes through the lifetime of great albatrosses, and show that attraction differed between age classes, sexes and personality. Juveniles encountered fewer vessels than adults, but also showed a lower attraction to vessels when encountered. Attraction rates, especially for fishing vessels, increased through immaturity to peak during adulthood, decreasing with old age. Shy females had lower attraction to vessels and shy males remained at vessels longer, suggesting that bolder individuals may outcompete shyer ones, with positive consequences for mass gain. These results suggest that attraction to vessels is a learned process, leading to an increase with age, and is not the result of preferential attraction to new objects by juveniles. Overall, our findings have important conservation implications as a result of potential strong differential selection on the risk of bycatch for age classes, personality types, populations and species.

Spatial segregation in a sexually dimorphic central place forager: Competitive exclusion or niche divergence?

Sexual competition is increasingly recognized as an important selective pressure driving species distributions. However, few studies have investigated the relative importance of interpopulation versus intrapopulation competition in relation to habitat availability and selection. To explain spatial segregation between sexes that often occurs in non-territorial and central place foragers, such as seabirds, two hypotheses are commonly used. The 'competitive exclusion' hypothesis states that dominant individuals should exclude subordinate individuals through direct competition, whereas the 'niche divergence' hypothesis states that segregation occurs due to past competition and habitat specialization. We tested these hypotheses in two populations of an extreme wide-ranging and sexually dimorphic seabird, investigating the relative role of intrapopulation and interpopulation competition in influencing sex-specific distribution and habitat preferences. Using GPS loggers, we tracked 192 wandering albatrosses Diomedea exulans during four consecutive years (2016-2019), from two neighbouring populations in the Southern Ocean (Prince Edward and Crozet archipelagos). We simulated pseudo-tracks to create a null spatial distribution and used Kernel Density Estimates (KDE) and Resource Selection Functions (RSF) to distinguish the relative importance of within- versus between-population competition. Kernel Density Estimates showed that only intrapopulation sexual segregation was significant for each monitoring year, and that tracks between the two colonies resulted in greater overlap than expected from the null distribution, especially for the females. RSF confirmed these results and highlighted key at-sea foraging areas, even if the estimated of at-sea densities were extremely low. These differences in selected areas between sites and sexes were, however, associated with high interannual variability in habitat preferences, with no clear specific preferences per site and sex. Our results suggest that even with low at-sea population densities, historic intrapopulation competition in wide-ranging seabirds may have led to sexual dimorphism and niche specialization, favouring the 'niche divergence' hypothesis. In this study, we provide a protocol to study competition within as well as between populations of central place foragers. This is relevant for understanding their distribution patterns and population regulation, which could potentially improve management of threatened populations.