Schooling with dolphins
Kathy Heise searches for what's bringing the dolphins back
by Stephen Forgacs
Last summer, Kathy Heise came a little too close to becoming part of a food chain she wouldn't normally associate herself with.
Heise, a Zoology doctoral student, was studying seabirds from a blind set up on a small rocky island about 10 kilometres from shore near Hudson Bay when a couple of polar bears waded ashore.
The bears, although primarily interested in dining on the ground-nesting birds and their eggs, stalked Heise and her two colleagues for two days, hardly deterred even by shotgun blasts. After using a radio-telephone to call for help, Heise assembled a small Zodiac and returned to the mainland to pick up two Inuit and an RCMP officer who had travelled eight hours in a four-wheel drive vehicle to meet her. Back on the island they too were unsuccessful in persuading the bears to leave.
"After six days of bear occupation we finally loaded our gear into the Zodiac and left. And, at the rate the bears were going through eggs, we could tell that very soon there wouldn't be any nests left to study.
"I learned a few valuable lessons about how to behave when confronted by polar bears through that experience," Heise says, from the relative safety of her office in a UBC hut.
While last summer's experience may have given Heise a new interest in polar bears, or in avoiding them, her real research interest remains a much friendlier creature -- the Pacific white-sided dolphin.
Thousands of British Columbians and visitors have had at least a brief encounter with Pacific white-sided dolphins, thanks to the presence of White Wings in the killer whale pool at the Vancouver Aquarium. Now even more are becoming acquainted with the species thanks to its reappearance in the past decade along the B.C. coastline, particularly north of Campbell River on Vancouver Island and up the central coast. Since 1992, the dolphins have also been regularly sighted in the inshore waters of southeastern Alaska, and sightings in the inshore waters of Georgia Strait are becoming more common.
Heise's interest in the dolphins was sparked in 1986. While working as a lighthouse keeper, she detected the dolphins' distinctive vocalizations on a hydrophone set up to monitor killer whale activity, and saw a school of several hundred dolphins moving through Johnstone Strait.
"Hearing the dolphins came as a surprise after five years of seeing and hearing only killer whales," Heise says.
The question of why the dolphins -- usually considered inhabitants of offshore waters -- have appeared along the coast led Heise to UBC and became the subject of her master's thesis.
The recovery of dolphin teeth from aboriginal midden sites near Queen Charlotte Strait and on several Gulf Islands suggests dolphins have travelled the coast for at least 2,000 years. Sightings in B.C. waters though have been relatively rare since the first was officially recorded in 1900.
A survey conducted by Heise of hundreds of mariners revealed that while a number of people recalled seeing dolphins along the B.C. coast in the 1940s, '50s and '60s, sightings of the Pacific white-sided dolphin dropped off dramatically between the late 1970s and mid-1980s.
Now the acrobatic dolphins, which can live to be as old as 46 years, are seen frequently along the coast, travelling in schools as small as two and as large as 1,000. The fact that white-sides are attracted to boats -- they often bow ride, surfing the water swell in front of a boat -- contributes to making an accurate population count difficult, says Heise. The same group could easily be counted again and again. With no firm results, estimates of the Pacific white-sided dolphin population in the North Pacific run from 50,000 to 4.5 million.
In seeking to find reasons for the white-side's reappearance, Heise set out to record the life history parameters of the dolphin -- such as lifespan, breeding cycles, and size -- while also examining its diet and collecting information on its range.
Heise considered three possible explanations for the dolphin's reappearance in the mid- to late 1980s. An obvious explanation could simply be that population growth accounted for the dolphin sightings off B.C. However, after evaluating factors including lifespan, age at sexual maturity and annual pregnancy rate, Heise determined that the population appears stationary, and that population growth was therefore an unlikely explanation for the dolphins' sudden appearance.
She also considered the impact of the high seas fishery, notably the Japanese flying squid driftnet fishery which is estimated to have caused the death of 49,000 to 89,000 white-sided dolphins between 1978 and 1990 before being closed in 1992.
Since the dolphins' reappearance on the B.C. coast occurred while the fishery was taking a toll on dolphin populations, a possible explanation was that the white-sides, faced with driftnets in the open ocean, had sought the relative safety of coastal waters. However, since thousands of dolphins remain along B.C.'s coast more than five years after the squid fishery ended, it too seemed an unlikely reason for their appearance.
Finally, Heise turned to a "regime shift" explanation which considers factors such as climate and water temperature changes and related changes in various fish stocks, such as salmon, herring and anchovy.
Heise points to evidence that certain fish populations, such as sardine and anchovy -- both of which are prey of Pacific white-sided dolphins off California -- appear to fluctuate at intervals of 60 to 100 years. Sardines, abundant off the B.C. coast until the mid-1940s, are making a comeback in California and since 1996 have reappeared in B.C. waters.
Fluctuations of marine species such as zooplankton, sea birds, herring, salmon and other forage fish species also suggest a link to a regime shift in the North Pacific that began in 1976-77, says Heise. An earlier regime shift from warm to cool temperatures took place during the winter of 1946-47.
Examining the stomach contents of dolphin carcasses combined with hours observing them feed and then identifying the remnants, has helped Heise determine the species' sources of food. Pacific white-sided dolphins from B.C. to Japan have a diet ranging from salmon, squid, herring and anchovy to the odd jellyfish. The dolphins Heise studied off B.C. seemed to show a preference for salmon and herring.
But Heise stops short of a definite link between past and recent changes in climate, the effect those changes have on fish stocks, and the reappearance of the dolphins.
"Unfortunately we don't have enough historical evidence of dolphin abundance to link the earlier regime shift with changes in dolphin distribution," she says.
While Heise acknowledges the many unanswered questions remaining about the Pacific white-sided dolphins' reappearance, her compilation of information and research into the dolphins' diet represents a step toward understanding the animal and its behaviour.
Heise remains deeply interested in the dolphins, but has broadened the scope of research for her PhD to look at food-chain-related interactions between forage fish, marine mammals and seabirds.
And, in the months of research that lie ahead, Heise hopes to build on her knowledge of the marine mammal food chain, without becoming part of it.