by Frances Robertson
In August 2005 I found myself with the opportunity to volunteer on a minke whale research project in the San Juan Island of Washington state. With a few last minute changes to my previous plans, I ended up spending the remainder of the summer as a research assistant to minke whale researcher Dr. Jonathan Stern.
I had previously been involved in research on northern and southern resident killer whales and harbour porpoise in Orkney, Scotland, so this was my first real introduction to baleen whale research.
Over the following six weeks, we encountered and identified at least seven individual whales, all of whom we affectionately named after 1970s rock stars such as Joni Mitchell and Johnny Rotten.
We tracked most animals for one to three hours, but one whale took us on a seven-hour jaunt across the Strait of Jaun de Fuca towards Port Townsend! We all agreed that our dinner of crab cakes was well deserved that day.
We also encountered harbour and Dall’s porpoise, southern resident killer whales, the Lopez grey whale and even had a close encounter with a rather lost juvenile Brown Booby…but that is another story.
Minke research past and present
Minke whale research in the northeast Pacific began in the early 1980’s around the San Juan Islands, Washington, with a behavioural study based on the recognition of individual animals using photos. The success of this work lead to similar studies in Monterey Bay, California and Johnstone Strait, British Columbia.
In each study, a catalogue of photos documenting scars and distinguishing characteristics of individual whales was created. In total, the three studies identified less than 60 individual whales. None of these whales were seen in more than one study area, suggesting that the minke populations in each area are separate.
During 11 years of studies in the San Juan Islands, 30 individual minke whales were photographed and identified. Some of these whales showed “site fidelity”, returning to the same area throughout the summer and also from year to year. In addition to site fidelity, the whales were also faithful to particular feeding methods. Researchers identified three core areas used by minkes during the study (see map), determining that whales in different areas consistently used one feeding method. Minke whales in Areas A and B, to the north of San Jaun Island and San Juan Channel, consistently used lunge feeding to capture prey while whales that frequented Area C, the banks to the south of San Juan Island, used bird-associated feeding to capture prey. Most whales were observed using the same feeding method over two or more years.
In the 1990’s, minke whales were only found in Area C, to the south in the Strait of Juan de Fuca, despite continued search efforts in all three areas. This coincided with a general decline of herring due to disturbance of adjacent herring spawning grounds and with an apparent decline in the overall number of seabirds in the area.
In contrast, we found minke whales in all three areas during our 2005 fieldwork. We also noticed that the number of the birds in the area seemed higher than it had been in recent years. In total, we identified at least seven individual minke whales.
An interesting result of this summer’s fieldwork was the realization that individual whales may have greater ranges than previous studies had indicated. We photographed one whale on the banks to the south of San Juan Island in Area C and also around Waldron Island in Area A (see photo). Another whale with a collapsed dorsal fin that we photographed in Area A in August had been sighted by a whale watching vessel in Area C, near McArthur Bank, in June.
We are currently working with the Whale Museum in Friday Harbour to produce a San Juan Minke Whale Identification Guide for the whales that have been photo-identified over the past few years.
There remain many questions to be answered about the size and growth rate of minke whale populations in the northeast Pacific. The U.S. National Marine Fisheries Service (NMFS) has estimated that a maximum of 1,015 minke whales inhabit the coastal waters of California, Oregon, and Washington. Given that blue and humpback whale populations in the same area are estimated at 1,744 and 1,034 individuals respectively and that these species were targets of commercial whaling in these waters while minkes were not, the minke population is unusually small. This raises questions about the underlying causes for minkes’ rarity. For example, we would expect that minke populations might have grown dramatically when commercial whaling dramatically reduced the numbers of other baleen whales, therefore reducing competition for food resources. The fact that this did not occur suggests that minke whales may be part of a different ecological community from larger baleen whales, an idea that could be explored in future research.
Further research is also needed to determine the size and trajectory of the minke whale population in BC waters.
Dorsey et. al., Minke whales (Balaenoptera acutorostrata) from the west coast of North America: Individual recognition and small scale site fidelity, Report for the International Whaling Commission (Special Issue 12) 357-368
Hoelzel, R. A., Dorsey, E. M., and Stern, S. J., (1989), The foraging specializations of individual minke whales, Animal Behaviour, 38, 786-794
Hoelzel, A.R. and Stern, S.J. 2000. Minke Whales. Voyager Press