The Role of Dive and Foraging Behaviors in Ship Strikes

Like foraging marine animals, humans rely disproportionately on productive coastal areas created by upwelling. Particularly sensitive cetaceans are vulnerable to anthropogenic inputs when they converge with human activities. These inputs range from contaminants and toxins to entanglement in marine debris and noise, which affects communication, causes hearing loss and displacement, and even causes mass stranding. The most direct interaction between humans and whales occurs when a ship physically strikes a whale. Off the west coast of the United States, blue, fin, humpback, and gray whale deaths are linked to ship strikes annually. In 2007 after four blue whale deaths were attributed to ship strikes, conservation groups began pushing for greater protection. Researchers analyzed the overlap between whale habitat and ship traffic, prompting an amendment to the major shipping lanes off San Francisco and Santa Barbara in June. Despite initial measures, ship strikes continue, and many questions remain about the behavior of whales in shipping lanes, how behaviors increase the risk of ship strikes, and how ships affect behavior. From August to October we tagged 12 whales in the major shipping lanes off San Francisco with time-depth-GPS tags. By pairing geospatial locations of whales and ships with behavior, we can assess close encounters and determine if the presence of ships directly affects behavior. And by examining whale dive parameters (dive type, descent and ascent speed, dive duration, dive depth, and surface time) with respect to whale group composition and size, age class, sex, prey layer, ship presence, and time of day, we can characterize whale dive and foraging behaviors in and around shipping lanes to understand which factors put them most at risk of potentially fatal ship strikes.

Speaker: Angela Szesciorka