Can nearshore seabirds detect variability in juvenile fish distribution at scales relevant to managing marine protected areas?

Juvenile recruitment is an important determinant of change within marine protected areas (MPAs). Understanding spatio-temporal variability in recruitment rates will help managers set realistic expectations for rates of population and community level change within individual MPAs. Here we ask whether seabird foraging rates can be used as a proxy for juvenile fish recruitment at spatial scales relevant to MPA management. We investigated the foraging rates of six piscivorous seabirds inside and outside of three island and four mainland MPAs in Southern California and compared these rates to estimates of juvenile fish density from kelp forest surveys conducted at the same sites during the same 2years (2012 and 2013). Juvenile fish communities at island and mainland sites were dominated by three families, Embiotocidae, Labridae and Pomacentridae, in both years. Additionally, there was an influx of young-of-the-year rockfishes (family Sebastidae) at most sites in 2013. Seabird and fish distributions were similar at the regional (approximately 15-30km) scale, but less similar at the site-specific scale. Site-specific differences reflected differences in the diet and foraging habits of individual seabird species. While fish surveys were specific to the kelp forest habitat, seabirds were sampling multiple habitats (i.e. multiple water depths over multiple bottom substrates) within a given site. Our results suggest that integrating seabird data with data on juvenile fish abundance can produce a more holistic index to proxy spatio-temporal variability in juvenile fish recruitment. In other words, seabird studies can provide additional information not captured by fish surveys and help resource managers better understand local patterns of fish recruitment at the community level. This will help resource managers establish realistic expectations for how quickly fish populations should change within individual MPAs.