UC San Diego

Characterization of the spatiotemporal patterns of marine mammal populations is challenging yet critical for understanding their role in the ecosystem and how they are affected by ecological disturbance, such as anthropogenic activity. Gathering information about deep-diving cetaceans is particularly difficult because they spend so much of their lives well below the ocean's surface, however they can be detected using passive acoustic monitoring. The Gulf of Mexico is home to at least six species of deep-diving cetaceans, and we recorded signals from Ziphius cavirostris, Mesoplodon europaeus, M. densirostris, Physeter macrocephalus and Kogia spp., as well as an unknown beaked whale-like signal. Using seafloor High Frequency Acoustic Recording Packages (HARPs) we monitored nearly-continuously at three deep- water sites (>900m depth) using a 200 kHz sampling rate, from May 2010 until February 2012, accumulating more than 1350 cumulative days of data. Here I describe the species present, their detection trends over time and their relationships with the environment, including the Deepwater Horizon oil spill. This major environmental event took place in the northern Gulf of Mexico for roughly three months in the summer of 2010, and released approximately 210 billion gallons of oil and unmeasured amounts of natural gas mixed with chemical dispersants into the deep water along the continental slope. The number of detections for each species fluctuated across sites on diel and seasonal time scales. Beaked whales were detected at a remarkably high rate at one site. Sperm whales were detected almost daily at another site. Kogia spp., which are very difficult to monitor visually, were easily detected acoustically and were present at all three sites. I used mathematical models to relate acoustic detections of the different species to their environment. The models included both natural and anthropogenic factors, with data collected both in situ and remotely. Most models include mean sea surface temperature, indicating the importance of seasonal variations and the resulting ecological fluctuations. The results vary by species and location, and help us understand the ecology of these rare species as well as the potential impact of the oil spill on the region