Threatened and Endangered Species - Status Reports
Date Published: March 2004
Number of Pages: 120
Author(s): Gary J. Wiles
Killer whales are distributed throughout the marine waters of Washington. Four populations are recognized and are referred to as southern residents, northern residents, transients, and offshores. These populations rarely interact and do not interbreed despite having largely sympatric year-round geographic ranges that extend into British Columbia and other areas along the west coast of North America. Southern resident and transient killer whales are the only populations that regularly enter the state's coastal waters, whereas offshore whales mainly inhabit open ocean off the outer coast. Northern residents are rare visitors to the state. Resident killer whales are believed to feed almost exclusively on salmon, especially chinook, and other fish. They occur in small highly stable social units known as matrilines, in which all individuals are maternally related. Pods are larger social groups comprised of several matrilines and typically hold about 10 to 60 whales. In contrast, transient whales feed primarily on harbor seals and other marine mammals. They also travel in small matrilineal groups, which typically contain one to six animals. Although some matriline members maintain long-term bonds, the social organization of transients is generally more flexible than in residents. Few details are known about the biology of offshore killer whales, but they commonly occur in large groups of 20-75 individuals and are believed to be mainly fish-eaters.
The southern resident population is comprised of three pods (identified as J, K, and L pods) and is most familiar to the general public. It occurs primarily in the Georgia Basin and Puget Sound from late spring to fall, when it typically comprises the majority of killer whales found in Washington. The population travels more extensively during other times of the year to sites as far north as the Queen Charlotte Islands in British Columbia and as far south as Monterey Bay in California. Southern resident population trends are unknown before 1960, when roughly 80 whales were present, but it is quite likely that numbers were at a depleted level due to indiscriminant shooting by fishermen. The population is believed to have recovered somewhat during the early and mid-1960s, but live-captures for aquaria removed or killed at least 47 of the whales during the 1960s and 1970s. The population has been closely monitored since 1974, with exact numbers of animals and other demographic details learned through annual photo-identification surveys. Membership increased from 70 to 98 whales between 1974 and 1995, but this was followed by a rapid net loss of 18 animals, or 18% of the population, from 1996-2001. J and K pods have generally maintained their numbers during the decline, with both equaling or exceeding their largest recorded sizes in 2003. However, L pod, which comprises about half of the southern resident population, has been in sharp decline since 1994. This pod's decline is especially worrisome because it involves both increased mortality of members and a reduction in birth rates.
Population trends of transient and offshore killer whales are not known because of their greater mobility and more sporadic occurrence, making it difficult for researchers to maintain detailed photographic records of both groups. Both populations cover huge geographic ranges that extend from Alaska to southern California.
Three threats have been identified as potentially the most problematic for killer whales in Washington. First, the southern residents have experienced large historic declines in their main prey, salmon. Overall salmon abundance has remained relatively stable or been increasing in Puget Sound and the Georgia Basin during the past several decades and therefore may not be responsible for the decline in L pod since 1996. However, a lack of comprehensive information on the status of all salmon runs in the range of the southern residents makes the threat of reduced prey availability difficult to dismiss. Second, recent studies have revealed that transient and southern resident whales are heavily contaminated with organochlorine pollutants, primarily PCBs and DDT residues. Both populations are now considered as among the most highly contaminated marine mammals in the world. Lastly, increasing public interest in killer whales has fueled tremendous growth in whale watching in and around the San Juan Islands during the past two decades. As a result, southern resident whales are now followed by significant numbers of commercial and private vessels during much or all of the day when residing in this portion of their range. Despite the great increase in killer whale research in Washington and British Columbia since the early 1970s, researchers remain divided on which of these threats are most significant to the whales. It may well be that a combination of threats are working to harm the animals, especially L pod. Until more complete information becomes available, it is best to take a precautionary management approach in determining appropriate conservation strategies for the species.
For these reasons, the Department recommends that the killer whale be listed as an endangered species in the state of Washington.
Wiles, G. J. 2004. Washington State status report for the killer whale. Washington Department Fish and Wildlife, Olympia. 106 pp.
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