Publication Date

Fall 2009

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


James T. Harvey

Subject Areas

Biology, Ecology.; Biology, Oceanography.; Biology, Zoology.


The coastal upwelling ecosystem near Monterey Bay, California is an extremely productive, yet variable, ecosystem and an important foraging area for mobile, apex predators, such as marine mammals. Longer-term studies are required to better understand how marine mammals respond to temporal environmental variability; however, few of these studies exist. We conducted monthly shipboard line-transect surveys in Monterey Bay from 1997 to 2007, concurrent with hydroacoustic and oceanographic sampling. Twenty-two species of marine mammals were identified, and monthly and annual densities were calculated for the 12 most commonly sighted species. Densities varied among years, whereas species richness remained relatively constant. Marine mammals were most evenly distributed but least dense during the anomalous upwelling conditions of 2005 and least even but still dense during the 1997/1998 El Nino event. No single environmental variable consistently predicted the densities of cetacean species, and variables expected to be good predictors explained only a minimal amount of variability. Incorporating temporal lags into analyses improved predictive capabilities of upwelling index, chlorophyll, and primary productivity, but a more comprehensive prey collection methodology may also have improved predictive power. Through long-term monitoring programs, we can expand our understanding of how environmental variability affects top predators and become better prepared for future oceanic change as it occurs.