A landmark study on seabird migration in the tropical Indian Ocean has unveiled patterns of dispersal and habitat use that challenge current paradigms of marine predator distribution. The research, led by Alice M. Trevail and colleagues, focuses on non-breeding seabirds, highlighting their wide dispersal across the tropical Indian Ocean, divergent habitat use, and the absence of localized aggregations. This study, which tracked 348 individuals from 9 species across ten colonies, reveals a diffuse species richness covering over 3.9 million square kilometres​​.
The study emphasizes the urgent need for protection in tropical marine ecosystems, which is crucial for arresting catastrophic biodiversity loss. The widespread distribution of seabirds and their varied habitat preferences present significant challenges in implementing effective conservation strategies. These seabirds, critical for tropical ecosystem function, particularly coral reef conservation, have suffered from habitat destruction, human exploitation, invasive species, and overfishing​​.
The researchers observed that the seabirds’ at-sea distributions covered large areas, with individual tracks overlapping within and among species. Despite occupying broadly similar regions, the species responded differently to environmental variables, indicating specific habitat preferences​​. The observed species richness was consistent throughout the year, emphasizing a homogeneous distribution of species richness across the tropical Indian Ocean​​.
While some of the largest Marine Protected Areas (MPAs) in the eastern Indian Ocean were visited by most of the tracked species, most of the high species richness occurred in the unprotected high seas beyond national jurisdictions. This finding underscores the need for an ocean-wide perspective in conservation efforts, including high-seas legislation​​.
The study’s findings starkly contrast with patterns observed in other ocean basins, where marine predator aggregations in productive and predictable zones have been successfully targeted for spatial protection. In the tropical Indian Ocean, the diffuse patterns of diversity and large winter ranges of seabirds necessitate a different approach to conservation​​.
The current MPA network, while beneficial, is not sufficient to cover the full extent of maximum species richness areas. The researchers suggest that MPAs may benefit both locally breeding seabirds and itinerant non-breeders, yet a more extensive and international approach is needed to ensure effective conservation​​.
The study acknowledges limitations, such as focusing on nine tracked species, representing about one-third of breeding seabirds in the region, and excluding widely dispersed species like Sulidae and Fregatidae. This approach likely underestimates the total species richness, especially in the Southern Ocean off the western coast of Australia​​.
In conclusion, the study highlights the importance of the high seas for migratory seabird diversity and calls for large-scale conservation efforts beyond area-specific protection. As terrestrial restoration improves breeding habitat conditions and environmental change reshapes marine conditions, global thinking and societal changes are needed to ensure suitable at-sea environments for seabirds into the future​​.
Citation: Trevail et al. 2023. Tracking seabird migration in the tropical Indian Ocean reveals basin-scale conservation need, Current Biology, DOI: 10.1016/j.cub.2023.10.060
