National Marine Sanctuaries capture enhanced abundance and diversity of the California Current Ecosystem avifauna

Quantifying the spatial patterns of marine predators, such as seabirds, reveals areas of ecological importance and associated food web characteristics, upon which marine conservation and management plans can be based. Owing to high productivity, the California Current Ecosystem (CCE) harbors an abundant and diverse avifauna comprised of resident and migratory species. With a goal of protecting habitats in three biogeographic regions — North, Central, and South CCE — a network of marine protected areas have been designated, including five National Marine Sanctuaries (NMS). Using an extensive at-sea survey dataset (1980 to 2017), we characterize spatial patterns of seabirds, and compare mean relative abundance, diversity, and community composition both within and outside the NMSs. We found that within the CCE, seabird abundance and diversity increase linearly from south to north (R² = 0.54 and R² = 0.55, respectively) and decrease linearly with distance from the coast (R² = 0.16 and R² = 0.23, respectively). The avifauna of the North and South regions are the most distinct, with the Central region being transitional between the two. The CCE avifauna shows limited overall diversity, with just 10 species contributing >93% of abundance totals. In addition, certain foraging guilds and prey preference groups were dominant: pursuit-feeding and piscivorous species in the North and surface feeding generalists in the South. Overall, seabird relative abundance and diversity are higher within NMS boundaries compared to outside. Although relative abundance and diversity of seabirds within NMSs were broadly representative of corresponding biogeographic regions, the overall NMS network captures a range of distinct seabird communities. The analysis of this extensive dataset provides a better understanding of seabird spatial patterns and their ecological roles within different regions, thus facilitating more effective, adaptive management of CCE biotic resources.