Gray Whales in San Francisco Bay

Guy Oliver (1), Jamie Gilardi (1), Caitlyn Toropova (1), Pieter Folkens (2), Kate Cronin (1), Natasha Bodorof (3) Kristen Sanchez (3), Damon Wolf (4), Kathryn
Zagzebski (5) and Birgit Winning (1)

1 Oceanic Society
2 Alaska Whale Foundation
3 UC Santa Cruz
4 Sonoma State University 5 Marine Mammal Center

While gray whales, Eschrichtius robustus, utilize lagoons of Baja California andhistorically, San Diego Bay, they have been rare in San Francisco Bay.Only a single gray whale has been found in the middens surrounding theBay and whaling records do not indicate their presence within the Bay.

Since 1997 reports of gray whales within the Bay have become increasingly common even though the Bay is surrounded by a population of over 6,000,000 humans and is one of the busiest seaports in the United States. In 1999 the Oceanic Society initiated a program to document this new pattern consisting of opportunistic and systematic hipboard surveys, a network of Bay users to report sightings and a photo-id catalog of individual whales.

In 1999 gray whales were found within the Bay on 39 days, in 2000 on 64 days, and so far in 2001 on 116 days. Over 95% of all sightings have occurred during the northbound migration, February through May. Whales of all age classes have been observed, although the majority have been juveniles between 25 and 37 feet in length. Whales have been bserved from the extreme southern to the extreme northern ends of the Bay, with the preponderance of sightings occurring in the middle portion. They have been observed traveling, milling, socializing and foraging.

While numerous studies have documented that shipping and acoustic disturbance cause cetaceans to abandon traditional habitats and alter their migration routes, this is the first study to demonstrate a cetacean species expanding its usage into such a heavily trafficked environment. While individual residence times remain unknown, there is concern that foraging whales are exposed to toxic contaminants in the sediments. Additionally, proposed bridge and airport construction may cause increased disturbance sufficient for the whales to cease utilizing the Bay.