ABSTRACT: Vessel traffic may have contributed to southern resident killer whales Orcinus orcabecoming endangered. To determine the importance of this threat, we measured the behavior ofsouthern residents in the presence and absence of vessels from 2003 to 2005 at 2 different sites alongSan Juan Island, Washington, USA. We observed activity states of killer whale schools using scansampling and collected information on the number of vessels present at various distances from those.We use first-order, time-discrete Markov chains to estimate state-transition probability matricesunder varying boat exposure conditions. Transition probabilities between activity states were significantlyaffected by vessel traffic. In addition, there was a reduction in time spent foraging, as estimatedfrom the stationary state budget from the Markov chains, confirming an effect also previouslyobserved in northern resident killer whales. If reduced foraging effort results in reduced prey capture,this would result in decreased energy acquisition. Each school was within 400 m of a vessel mostof the time during daylight hours from May through September. The high proportion of time southernresident killer whales spend in proximity to vessels raises the possibility that the short-termbehavioral changes reported here can lead to biologically significant consequences.

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M. Bradley Hanson, Robin W. Baird, John K. B. Ford, Jennifer Hempelmann-Halos, Donald M. Van Doornik, John R. Candy, Candice K. Emmons, Gregory S. Schorr, Brian Gisborne, Katherine L. Ayres, Samuel K. Wasser, Kenneth C. Balcomb, Kelley Balcomb-Bartok, John G. Sneva, Michael J. Ford (2010).  Endang Species Res Vol. 11: 69-82, 2010

ABSTRACT
Recovery plans for endangered southern resident killer whales Orcinus orca have identified reduced prey availability as a risk to the population. In order to better assess this risk, we studied prey selection from 2004 to 2008 in 2 regions of the whales’ summer range: San Juan Islands, Washington and the western Strait of Juan de Fuca, British Columbia. Following the whales in a small boat, we collected fish scales and tissue remains from predation events, and feces, using a fine mesh net. Visual fish scale analysis and molecular genetic methods were used to identify the species consumed. Chinook salmon, a relatively rare species, was by far the most frequent prey item, confirming previous studies. For Chinook salmon prey, we used genetic identification methods to estimate the spawning region of origin. Of the Chinook salmon sampled, 80 to 90% were inferred to have originated from the Fraser River, and only 6 to 14% were inferred to have originated from Puget Sound area rivers. Within the Fraser River, the Upper Fraser, Middle Fraser, South Thompson River and Lower Fraser stocks were inferred to currently be sequentially important sources of Chinook salmon prey through the summer. This information will be of significant value in guiding management actions to recover the southern resident killer whale population.

FULL PAPER HERE

Ford, John K.B., Graeme M. Ellis (2005). . Canadian Science Advisory Secretariat Research Document – 2005/041.

ABSTRACT

Three distinct, socially-isolated forms, or ecotypes, of killer whales (Orcinus orca), inhabit coastal waters of British-Columbia, Washington State, and southeastern Alaska. The so-called transient ecotype feeds primarily on marine mammal prey, the resident ecotype feeds primarily on fish, and the diet of the offshore ecotype is not known. A previous study of the diet of the resident and transient ecotypes using opportunistic collection of prey remains from kill sites as a primary measure of prey selection found that resident killer whales feed predominantly on salmonids, particularly on chinook salmon (Oncorhynchus tshawytscha). To address uncertainties concerning potential biases in the prey fragment sampling technique and questions regarding seasonal and geographic variability in diet, we conducted field studies of foraging behaviour during 1997-2004. Foraging by resident killer whales often involves cooperation among kin-related group members, and prey items are frequently shared by two or more whales. Adult males share prey less often than do females and subadults. Prey sharing does not appear to be related to prey size. Prey fragments left at kill sites result mostly from prey handling and sharing, and are reliable indicators of selection for different salmonid species by resident killer whales. Chinook is the predominant prey species taken by both northern and southern resident communities during May-August, but chum salmon (O. keta) is more prevalent in September-October, at least in northern residents. Coho salmon (O. kisutch) are taken in low numbers in June-October, but sockeye (O. nerka) and pink (O. gorbuscha) salmon are not significant prey species despite their high seasonal abundance. Non-salmonid fishes do not appear to represent an important component of resident whale diet during May-October. Their strong preference for chinook salmon may influence the year-round distribution patterns of resident killer whales in coastal British-Columbia and adjacent waters.

Full paper here.