Southern resident killer whales

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The research vessel Noctiluca of the Northwest Fisheries Science Center in close proximity to a killer whale

The southern resident killer whales (SRKW) represent the smallest of four resident communities within the eastern North Pacific Ocean. 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 as of 2005.[1] They are commonly referred to as the "orcas of the Salish Sea",[2] "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.[3] There are approximately 80 individuals that make up this small population. In 2012, two calves were born, one in J pod and one in L. One calf was born in 2013 but he did not survive. The world's oldest known killer whale, Granny or J2, belongs to the J pod of the SRKW population.[4] Her age is estimated at 103 years.

Social structure[edit]

Photo identification over the last 38 years has allowed researchers to track the southern resident population quite accurately, such as the Orca ID site[5] 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.[3] 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:[6]

Community
Southern Resident
Clan
J
Pods
J Pod (25 members)
K Pod (19 members)
L Pod (36 members)
Matrilines
J2, J4, J7, J9
K4, K7, K8, K11, K18
L2, L4, L9, L12, L21, L25, L26, L28, L32, L35, L37

Dialect[edit]

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.[3]

Location[edit]

The southern residents have reportedly been seen off the coast of Oregon, Washington, and Vancouver Island, British Columbia. Recently, they have 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, the Strait of Juan de Fuca, and southern Georgia Strait.[7] Little is known about their range and movements during the winter months.

Distinguishing features[edit]

  • 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.[8]

Diet[edit]

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:[3]

Threats[edit]

The major threats to this very small community have been listed as:[3]

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

Decline in prey[edit]

The depletion of large quantities of fish in the marine environments, while personal fishing in the salmon’s upstream spawning grounds have further depleted stock replenishment.[9]

Chemical contamination[edit]

Northwest killer whales are among the most contaminated marine mammals in the world, due to the high levels of toxic anthropogenic chemicals that accumulate in their tissues.[10] Implicated in the decline of Orca populations in the Pacific Northwest, these widespread contaminants pose a large problem for conservation efforts. While many chemicals can be found in the tissues of Orca, the most common are DDT, an insecticide, polybrominated diphenyl ethers, or PBDEs and polychlorinated biphenyls, or PCBs.[11] Each of these have detrimental physiological effects on orca,[12] and can be found in such high concentrations in dead individuals that those individuals must be disposed of in hazardous waste site.[13]

Correlative evidence shows orca may be vulnerable to effects of PCBs on many levels. Research has identified PCBs as being linked to restricting development of the reproductive system in orcas and dolphins.[14] High contamination levels leads to low pregnancy rates and high mortality in dolphins. Further effects include endocrine and immune system disruption, both systems being critical to mammalian health and survival.[15] A study examining 35 Northwest orcas found key genetic alterations that caused changes to normal physiological functions.[16] These genetic level interferences, combined with the varied effects of PCBs at other physiological levels, suggest these contaminants may be partially responsible for declines in Orca populations.

Marine noise[edit]

Noise and crowding from tour boats and larger vessels interrupt foraging behavior, or scare away prey.[17] Also, the sonar used by some ships and submarines is enough to cause hemorrhaging, and subsequently, death in some individuals[18]

See also[edit]

References[edit]

  1. ^ "The Endangered Species Act - Protecting Marine Resources". 
  2. ^ "Orcas of the Salish Sea". 
  3. ^ a b c d e http://www.nmfs.noaa.gov/pr/pdfs/recovery/whale_killer.pdf.
  4. ^ http://www.people.com/people/mobile/article/0,,20817101,00.html
  5. ^ "Center for Whale Research Whale ID". 
  6. ^ http://www.orcanetwork.org/news/birthsdeaths.html
  7. ^ http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/killerwhale.htm.
  8. ^ http://www.cascadiaresearch.org/robin/CJZkw88.pdf.
  9. ^ [Noakes, Donald J, Richard J Beamish, and Michael J Kent. "On the decline of Pacific salmon and speculative links to salmon farming in British Columbia."Aquaculture. 183.3-4 (363): 386.]
  10. ^ O'Neill, S, and J West. "Marine Distribution, Life History Traits, and the Accumulation of Polychlorinated Biphenyls in Chinook Salmon from Puget Sound,Washington." Transactions of the American Fisheries Societies. 138.3 (2009): 616-32.
  11. ^ [<http://conservationbiology.net/research-programs/killer-whales-2/> "Causes of Decline among Southern Resident Killer Whales." Center for Conservation Biology. University of Washington]
  12. ^ [Ross, P.S, G.M Ellis, et al. "High PCB Concentrations in Free- Ranging Pacific Killer Whales, Orcinus orca: Effects of Age, Sex and Dietary Preference." Marine Pollution Bulletin. 40.6 (2000): 504-515]
  13. ^ [<http://www4.nau.edu/tribalclimatechange/tribes/northwest.asp> "Fisheries Impact" by Tribes and Climate Change]
  14. ^ [<http://www.pbs.org/wnet/nature/episodes/the-dolphin-defender/the-effects-of-pcbs/806/> "The Dolphin Defender: The effects of PCBs." Nature]
  15. ^ [Ross, P.S, G.M Ellis, et al. "High PCB Concentrations in Free- Ranging Pacific Killer Whales, Orcinus orca: Effects of Age, Sex and Dietary Preference." Marine Pollution Bulletin. 40.6 (2000): 504-515.]
  16. ^ [Buckman, AH, N Veldhoen, et al. "PCB-Associated Changes in mRNA Expression in Killer Whales (Orcinus orca) from the NE Pacific Ocean."ENVIRONMENTAL SCIENCE & TECHNOLOGY. 40.23 (2011): 10194-10202]
  17. ^ [<http://wildwhales.org/conservation/threats/boat-disturbance/> "Boat Disturbance." Wild Whales]
  18. ^ [<http://www.canadiangeographic.ca/magazine/dec11/orcas_sound_pollution.asp> "Sound Pollution." Canadian Geographic]

External links[edit]