In April 2004, a visual and acoustic marine mammal survey component was added to the CalCOFI project to study cetacean ecology and habitat. Visual monitoring is conducted during quarterly cruises by experienced marine mammal observers using handheld 7x binoculars. Supplementary Bigeyes (25x magnification) or image stabilizer hand-held binoculars (18x magnification) are used for species identification when necessary. Visual monitoring provides excellent data for highly visible species in calm to moderate weather.
Concurrently, acoustic technicians survey with a towed hydrophone array during the transit between CalCOFI stations and with sonobuoys while on station, allowing collection of distribution data on vocal animals that may have been missed visually due to darkness, rough weather, distance from transect line, being underwater, or other reasons. Additionally, long-term acoustic monitoring is conducted at seven CalCOFI stations using bottom-mounted, High-frequency Acoustic Recording Packages (HARPs). These data will provide information on the annual and seasonal presence of cetaceans, and may be used to evaluate daily patterns of vocalization behavior. By integrating CalCOFI environmental and cetacean data, we plan to develop ecological models for cetacean habitat in the region offshore of southern California and to improve our understanding of their role in the California Current ecosystem.