The Southern Resident Killer Whales (SRKW) represent the smallest of four resident communities within the eastern North Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

. It is the only Killer Whale population listed as endangered by the U.S. Fish & Wildlife Service. It is currently protected under the Endangered Species Act

Endangered Species Act

The Endangered Species Act of 1973 is one of the dozens of United States environmental laws passed in the 1970s. Signed into law by President Richard Nixon on December 28, 1973, it was designed to protect critically imperiled species from extinction as a "consequence of economic growth and...

 as of 2005.
They are commonly referred to as the "Orcas of the Salish Sea", "fish-eating orcas", or the "SRKW" population. Unlike other resident communities, the SRKW is only one clan (J) that consists of 3 pods (J, K, L) with several matrilines within each pod. There are approximately 87 individuals that make up this small population.

Social structure

Photo identification over the last 30 years has allowed researchers to track the southern resident population quite accurately, such as the Orca ID site
offered through the Center for Whale Research. Their population is built upon a matrilineal system where these strong hierarchical groups of individuals are connected by maternal descent. Each matriline consists of a female, her sons and daughters and the offspring of her daughters; averaging anywhere from one to seventeen individuals and one to five generations within each of these matrilines. Pods are groups of matrilines that share a maternal ancestor, in which the southern residents consist of three pods. The number of individuals changes due to birth and deaths.

The Orca Network provides a list (last updated November 12, 2009). The following is the basic social structure:

Community

Southern Resident

Clan
Pods

J Pod (27 members)

K Pod (19 members)

L Pod (41 members)

Matrilines

J2, J8, J9, J16

K3, K4, K7, K18

L2, L4, L9, L12, L21, L25, L26, L28, L32, L35, L37, L45

Dialect

Similar dialects amongst pods create the social grouping called "clans". It is believed that the more similar their dialect is within the pods, the more closely related they are. The southern dialect is very different from other communities. For instance, northern residents use whistles as their main type of close-range communication and the southern residents use whistles for regular social interactions and long-range communications. Southern residents appear to be much more vocal but it could be due to their vocal usage during travel and the fact that they seem to travel more than the northern residents.

Location

The southern residents have reportedly been seen off the coast of Oregon, Washington, and Vancouver Island

Vancouver Island

Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...

. Recently, they've been spotted as far south as the coast of central California and as far north as the coast of Queen Charlotte Islands. During the Spring, Summer, and Fall, the southern residents tend to travel around the inland waterways of Puget Sound, Strait of Juan de Fuca, and southern Georgia Strait. Little is known about their range and movements within the winter months.

Distinguishing features

• Dorsal Fin: rounded at the tip (leading edge) and positioned over the rear insertion of the fin towards the back.

• Saddle Patch: typically seen as an "open" saddle patch; five different pigmentation patterns have been reported with similarities noted among clans within a community.

Diet

Southern residents are fish-eating orcas that appear to prefer the Chinook salmon to other fish species. From visual sources, necropsy, and feces collection, the following food preferences have been reported:

• Salmon 97%

  Chinook (78% in late spring and fall)

  Chum (11%, more so in Fall)

  Coho (5%)

  Steelhead (2%)

  Sockeye (1%)

• Other Fish 3%

  e.g., Pacific herring and Quillback rockfish

Threats

The major threats to this very small community have been listed as:

• Decreased prey availability
• Pollution and contaminants
• Effects from vessels traffic and vessel sound

External links

• http://www.nmfs.noaa.gov
• http://www.cascadiaresearch.org
• http://www.whaleresearch.com
• http://www.orcanetwork.org
• http://www.whalemuseum.org/index.html
• http://conservationbiology.net/research-programs/killer-whales/
• http://depts.washington.edu/fhl/
• NOAA Fisheries Service http://www.nwfsc.noaa.gov/features/kwsightings.cfm
• BC cetacean sightings network http://wildwhales.org/sightings/
• Cascadia Research http://www.cascadiaresearch.org/reporting_marine_mammal_sighting.htm