Investigation into potential range shifts of murrelet species in the Southern California Current Ecosystem

Anthropogenic climate change is warming our oceans and thus has the potential to dramatically alter marine ecosystems. Recent ocean temperatures have been shown to impact the distribution and availability of prey species, which may lead to periodic or permanent range shifts of the predators relying on them. Since seabirds are solely dependent on marine prey, changes in seabirds’ distribution may be valuable alerts for ecosystem health. We expand upon previous investigations of range and seabird community composition within the California Current Ecosystem (CCE) form 1980-2017 by selecting a “warm water” and “cool water” seabird species. We investigated these potential trends in Craveri’s murrelets (CRMU), the “warm water” species, and ancient murrelets (ANMU), the “cool water” species, as their northern and southern range, respectively, overlap in the southern CCE region. They are comparable in size, natural history, and prey type. We hypothesized that the trends in their distribution would reflect the northward expansion of warm water over time and periods of warm water associated with El Niño Southern Oscillation (ENSO). We expected CRMUs to increase in frequency and northward distribution over time and during El Niño events. For ANMUs, we expected to see a decrease in their frequency and a shift northward over time and with El Niño events. We calculated multiple linear regression models to analyze the relationships between species density (frequency of sightings/km2) with latitude, upwelling, and year. We found a decrease in density of both species and that latitude was the only significant predictor for both species’ density. This research will provide a foundation for future investigations of seabird range shifts in the CCE and assist in further understanding changes in upwelling ecosystems.