Big Year for Bigg’s Killer Whales
T36 and T137A - Photo by Dave Ellifrit/CWR
The Center for Whale Research (whaleresearch.com) has been monitoring Southern Resident and Bigg’s/Transient killer whale presence in the central Salish Sea and Puget Sound for more than 40 years.
2017 was a year of contrast in killer whale sightings. The Southern Resident killer whales were notably absent from what has historically been their “core summer habitat” from April through September with the lowest number of days sighted in the history of the Center for Whale Research’s Orca Survey. A similar trend was observed in 2013, when even J pod whales were absent for days and weeks at a time. These two years (2013 and 2017) have one thing in common: these years were among the three worst years for Chinook salmon returning to the Fraser River, using the Albion Test Fishery data as a proxy for abundance – not good news for these whales.
The Fraser River has historically hosted five aggregate runs of Chinook salmon, two with spring timing, two with summer timing, and one with fall timing. From the perspective of the Southern Resident killer whales, an abundant supply of Fraser River spring, summer, and fall Chinook salmon returning annually to the Fraser River to spawn could provide a steady diet for at least some of the J, K, and/or L pod whales from about April through September, with the highest concentrations of these salmon being found in the area known as the “core summer habitat” for the Southern Resident killer whales. The “core summer habitat” is the area in and around the San Juan Islands, about as far north as the Fraser River (Vancouver, BC), with the whales typically entering and leaving the area through the Strait of Juan de Fuca.
Studies have shown that Fraser River Chinook salmon comprise a significant portion of their diet when these whales are foraging in their “core summer habitat” or in the Strait of Juan de Fuca, to the south of Vancouver Island. In one study, research conducted during the months of May through September, 2004-2008, revealed that 80-90% of the Chinook salmon consumed by Southern Resident killer whales near the San Juan Islands and off the southern end of Vancouver Island originated from the Fraser River, with only 6‑14% originating from Puget Sound rivers (Reference 1). Research documented in a more recent publication also led to similar conclusions (Reference 2).
Given the whales’ historical use of the “core summer habitat”, the Fraser River Chinook salmon stocks are indeed important to these whales. However, these runs have been declining in recent years, with the Southern Resident killer whales notably absent from the “core summer habitat” during two exceptionally poor years.
In contrast, throughout 2017 sightings of killer whales in the central Salish Sea and Puget Sound were dominated by reports of Transient or Bigg’s killer whales. Some of the increase in sighting reports can be attributed to increased public awareness. However, the presence of Transient killer whales in this area is indeed on the rise. Contributing factors include growth in the West Coast Transient killer whale population as well as a plentiful supply of food in this area.
Although to the untrained eye these whales are similar in appearance to the Southern Resident killer whales, their diet is quite different. Transient killer whales rely on marine mammals (seals, sea lions, porpoise, etc.) for their food supply. Even though these whales face some of the same threats as the resident killer whales (in particular, toxins accumulating in their bodies due to their diet of marine mammals that consume fish), the West Coast Transient population is increasing in size. It is important to note that the Canadian Department of Fisheries and Oceans (DFO) maintains the West Coast Transient killer whale population data, assigns designations to new calves and “newcomers” to the region, and has primary responsibility for monitoring the population abundance, behavior, threats, and distribution throughout their range.
With support from DFO (www.pac.dfo-mpo.gc.ca), the Center for Whale Research (whaleresearch.com) has compiled the followed sighting details and sighting map of Transient killer whale encounters in 2017:
Transient killer whales were confirmed to be present somewhere in the central Salish Sea and/or Puget Sound areas on more than 280 days in 2017;
There were several days in 2017 when more than 45 Transients were present in the region, scattered about the area (see CWR encounter report: 2017encounters/70); and
Based on the data collected to date, it is estimated that more than 225 different individuals visited the area in 2017, including several new calves and some other individuals not previously documented in these waters. For 2015 and 2016, it is estimated that 165-175 different Transient killer whales visited the central Salish Sea and Puget Sound.
It will take CWR many months to finish compiling and validating 2017 Transient killer whale sightings.
(Derivative use of data originating from the Center for Whale Research requires prior approval).
NOTES:
This compilation of data would not be possible without the support of many individuals who contribute sighting reports and photos to the Center for Whale Research and Orca Network (www.orcanetwork.org). If you have sighting information to contribute to this project, please contact jane@whaleresearch.com.
If you happen to be out on the water, please be sure and follow the Be Whale Wise guidelines while in the vicinity of marine mammals of any kind (US: www.bewhalewise.org; Canada: www.pac.dfo-mpo.gc.ca)
References
(1) 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. Species and stock identification of prey consumed by endangered southern resident killer whales in their summer range. Endang. Species Res. 11: 69–82
(2) Ford, M. J., Hempelmann J., Hanson, M. B., Ayres, K. L., Baird, R. W., Emmons, C. K., et al. (2016) Estimation of a Killer Whale (Orcinus orca) Population’s Diet Using Sequencing Analysis of DNA from Feces. PLoS ONE 11(1): e0144956. doi:10.1371/journal.pone.0144956
(3) Cogan, J. 2015 Whale Sighting Report – Central Salish Sea and Puget Sound, Center for Whale Research, Friday Harbor, WA. 10 p.
https://docs.wixstatic.com/ugd/760f65_32964f6f770145e590bd7bfb7e463dea.pdf
