Spatial Patterns in Nearshore Juvenile Fish Abundance throughout the California Network of Marine Protected Areas as Revealed by Seabird Diet

The successful adaptive management of marine protected areas (MPAs) requires an understanding of spatial variability in the rates of juvenile recruitment to recovering populations. We used foraging rates of two coastally breeding, piscivorous seabirds to index juvenile fish recruitment to nearshore habitats at 46 sites throughout California’s MPA network. Each seabird species preys heavily on young-of-the-year and age 1 size classes of fish species that can benefit from MPA protections. We used mixed effects negative binomial regression to develop models relating foraging rates to coastal geography and annual upwelling strength and variability. The best models for both species included upwelling variability (i.e., persistent versus pulsed upwelling). The effects of upwelling variability differed depending on coastal geography. Foraging rates were highest in the lees of headlands and more stable against upwelling variability. For all other coastal configurations, pulsed upwelling led to higher foraging rates. Periods of relaxation in upwelling have been shown to reduce offshore transport of planktonic larvae, thereby increasing larval retention to nearshore habitats. Studies have also shown persistent recruitment in the lee of headlands where eddies form and retain larvae. Our results suggest that coastal geography should be considered when establishing realistic expectations for rates of community level recovery after MPA establishment and for prioritizing new areas for MPA designation. For example, an MPA established in the lee of a headland should show faster recovery rates than an MPA established along an exposed section of coastline due to more persistent larval delivery to leeward habitats. Our results also illustrate how the foraging rates of coastally breeding seabirds can provide a spatially explicit index to assess spatial and temporal trends in juvenile fish recruitment to nearshore habitats, thereby helping guide the adaptive management of MPAs.