Behavior and Ecology of Killer Whales in Monterey Bay, California
By Nancy Black, Richard Ternullo, Alisa Schulman-Janiger, Graeme Ellis, Marilyn Dahlheim, Peggy Stap

Summary research report of talk presented at
Fourth International Orca Symposium in France during Sept 2002

Introduction and Background

Monterey Bay (36°N 122°W) is located along the central California coast within a highly productive region of major upwelling. The Monterey Submarine Canyon is the most prominent bathymetric feature within the Bay and beyond, allowing for unique opportunities to study deep-water cetaceans in a near-shore environment.

Three known ecotypes (Residents, Transients, Offshore) of Killer Whales exist in the eastern North Pacific, and all have been sighted in Monterey Bay. Each can be distinguished by appearance and vocalizations at sea and have been differentiated genetically. Resident whales, which are well studied in the Pacific Northwest, travel and feed in predictable areas during summer months in inland waters of Washington state, Vancouver, B.C., and Alaska. They prey primarily on fish, live in closely associated family groups, and are very vocal. Transients in Monterey Bay are part of the west coast community of about 300 whales that range from southern California to southeast Alaska, prey on marine mammals, travel in relatively small groups, travel over long ranges, and are often vocally quiet. The Offshore type is least known, often travels in large groups of over 100 animals, many have nicked fins, and probably prey on fish and squid. A fourth type that has occurred periodically in Monterey Bay is the "LA Pod". No genetic samples have been obtained for this group, and they have never been seen in association with any other type.

Methods

Our methods for reaching the killer whales included use of 55-70' powerboats and a 22' inflatable. The study period for this report extended from 1987 through 2002. Our effort was both opportunistic, on whale watch vessels, and dedicated searches for killer whales on special projects funded by the BBC and National Geographic Society and on our own vessels throughout the study period. In addition a large sighting network is in place where various vessels reported killer whale sightings. Our research methods included photo-identifying individual whales and documenting their behavior, sighting locations and local movement patterns as well as collaborating with other scientists in the Pacific to document re-sightings in other areas.

Results and Discussion

Transients were most frequently sighted (223 sightings with photos from 1987-2002) and were highly associated with the canyon edge. Offshore (18 sightings) and LA Pod (9 sightings) sightings were found along canyon edges and also in inshore shallower waters.

Known prey of each killer whale type when feeding in Monterey Bay included for Transients: Gray whale calves, California sea lions, Harbor Seals, Elephant Seals, Dall's Porpoise, Pacific White-Sided Dolphins, Long Beaked Common Dolphin, and seabirds; Offshores: salmon, small schooling fish, and blue shark; Residents: Chinook salmon; LA Pod: Great White Shark (north of Monterey off Farallon Islands; Pyle et al. 1997). Prey was non-overlapping among types except both offshore and resident whales preyed on salmon.

As of September 2002, number of individual whales identified for each type included 145 transients, 172 offshores (min. numbers with 230 maximum), and 8 LA pod members. Within the transients, 36 were adult males, 7 females with no calves (over 10 sighting years), 24 reproductive females, and 78 juveniles/females/calves.

The Resident K and L Pods (part of southern Residents), which occur predictably during summer in Washington and Vancouver, were sighted once in Monterey Bay on January 29, 2000. This represents a distance of 1,251 km from their known summer range. During this day the whales foraged on Chinook salmon. This unusual event could represent declining food sources to the north and the whales' search for abundant prey elsewhere.

LA Pod whales ranged from San Francisco (central California) to the upper Sea of Cortez, with individual movements of 2,847 km. These whales were frequently sighted off Los Angeles, CA during the 1980's and a few times in Monterey during late 1980's and 1990's. They occurred off the West Coast of Baja and Sea of Cortez during this period as well. These whales were last sighted in December 1997 off San Diego, CA and may currently be residing in Mexico. Largest group size documented for these whales was 13, which is the known population for these individuals.

The Offshore whales traveled the longest distance for any Killer Whale type in the Pacific, with individuals sighted in Los Angeles, Monterey Bay and off Kodiak Island, Alaska, a distance of 3,680 km. Group sizes of these whales while in Monterey Bay differed seasonally. During winter months mean group size was 52 with maximum group size around 200 whales. Only one sighting occurred during spring with 22 whales, and during 8 sightings in fall, group sizes were small with a mean of 10 whales. No sightings occurred during summer, but offshores were sighted in British Columbia and Alaska during this period.

Transient whales were more frequently sighted in Monterey Bay compared to other types and therefore, more information has been gathered on them. The discovery curve of new adult male and female whales identified beginning in1987 slowly increased until 1999 where it leveled off, assuming now that most adults in this population that travel through and feed in Monterey have been identified.

Transient whales sighted in Monterey Bay have been identified from southern California to Southeast Alaska, with sightings within California, along the outer coasts of Oregon, Washington, British Columbia, and one sighting in inland waters of Southeast Alaska. The longest-range movement of four whales occurred from Monterey to Southeast Alaska, a distance of 2,594 km. Occurrence varied by season, with peak occurrence during spring and fall and few sightings during summer. Of the whales identified in Monterey and re-sighted to the north, 12 were sighted off Washington, B.C., and Alaska during summer months. Group size also varied by season, with the largest groups occurring during spring and smallest in summer. Many of the larger groups (32 was largest) were temporary associations of smaller subgroups over a day. Ninety-five percent of all identified whales were sighted in spring months over combined years. Whales that are rarely sighted were present more often during spring months and frequently sighted whales occurred more often during spring compared to other months. The higher occurrence, group sizes, and individual whale presence during spring corresponded with the migration of Gray Whale cow/calves through the Bay. The low sightings in summer could be due to Killer Whales shifting north with the pulse of mother/calf Gray Whales. As one example, an adult female sighted in Monterey on several occasions was also seen attacking a gray whale calf off Vancouver Island during summer.

Of the 24 documented reproductive females, 13 were sighted frequently enough to determine calving intervals. Since some whales may not be sighted for many months, there was a bias that calves may have been born and died before their mothers were re-sighted. Given this, years between calves ranged from 3 (n=1) to 12 (n=1) years; and in between: 4 years (n=1), 5 yr (n=1), 6 yr (n=2), 7 yr (n=3), 8 yr (n=3), 9 yr (n=1). Compared to other populations this rate appeared low and could be related to high levels of PCB's found in this group of killer whales.

Association pattern analysis indicated that transient whales occurred in 18 core groups of frequently sighted whales (up to 36 if infrequently sighted whales were included). Core groups were usually composed of 2-4 reproductive females with juveniles and calves, and some with one sprouter male or adult male. A few groups were composed of male pairs. These core groups of individuals were sighted together on more than 80% to 100% of the time. Two or more of these core groups joined together for temporary associations, especially during spring months while searching for and hunting Gray Whale calves. Three well-documented young males were sighted over a period of 10 and 11 years and are now sprouters and young adults. All still travel with their probable mothers with estimated current ages of 15 to 19 years.

This study represents the only long-term database for Killer Whales south of Washington State but part of the same population as whales to the north. Monterey Bay is a key area for detailed studies of the three known ecotypes and possibly five, as the ranges of these types may overlap in the region.

Distribution of Killer Whale types in Monterey Bay