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Volume 1 No 1: February 1997 |
'Urban' dolphins adapt to life in the
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AGAINST the odds, a pod of 50 dolphins has adapted its lifestyle, even its diet, to maintain a 'home and nursery' in one of Australia's most heavily-trafficked sealanes, Cockburn Sound.
 Prompted by employees' interest in the dolphins' behaviour around BP Kwinana Refinery's wharves, the company's management approached Murdoch University to research the Sound's dolphin population. The $140,000 study has provided some world firsts in behavioural studies of these gregarious mammals.But having closely observed the 'resident' dolphins for four years, Murdoch University researcher Bec Donaldson is still amazed at their powers to adapt so successfully to what she describes as 'an urban environment' vastly changed by human developments -- and still changing.In one of the project's world firsts in dolphin research, Bec Donaldson has focussed on following the development and behaviour of a single cohort of young dolphins -- from birth to their expected weaning this summer.Sanctuary The dolphins feed, breed, play and find sanctuary in an area which is increasingly as busy below the surface as it is on the surface -- given the seabed mining operations, movement of submarines and other warships from the base at Garden Island, the frequent passage of large bulk carriers and tankers, commercial fishing and the popularity of the area with water sports enthusiasts and recreational fishers.The Sound's seagrass areas would once have served as a fish nursery, providing a natural, abundant and diverse stock of fish for the dolphins, but Bec Donaldson has found that the resident pod seems to thrive on a much more restricted diet of mulies (pilch) and squid."This diet of smaller fish means the dolphins have had to change their feeding habits," she says. "They spend more time on the move foraging and less time resting than, for example, the dolphins at Monkey Mia in Shark Bay."That is not the only difference she has noted between the 'urban' dolphins and the more famous Monkey Mia dolphins."The Sound dolphins are much bigger and they do not have the speckled skin of the mature Shark Bay dolphins," she says.She also has been able to observe dramatically different behavioural patterns between the Cockburn Sound residents and their bottlenose dolphin cousins in Scotland's waters. The formation of male 'alliances' is one distinctive feature of dolphin behaviour Bec Donaldson has observed in the Cockburn Sound study.During the social development of young dolphins, from timid, dependent calves to gregarious, energetic adolescents, strong bonds begin to develop between small (two to four member) groups of males. These alliances, which appear destined to last for life, have not been observed at all by researchers observing Scotland's bottlenose dolphins.There seem to be several reasons for the alliances. Strength in numbers, when confronted by other males, is definitely one advantage for male dolphin 'bonding'."The alliances are so close that the members will even synchronise many of their activities," she says. "They'll leap together, breach or submerge in unison."It has been suggested that these displays may be to impress females, but it is more likely to demonstrate the strength of one alliance against another, without the need to fight."In the Cockburn Sound environment it seems to be natural for alliance members to work as a team to pursue, compete for and 'capture' the relatively few females that are available during any one mating season."In this respect, dolphins share something in common with primates in that they are highly political creatures," according to Bec Donaldson. "Like astute politicians, male dolphins will wheel and deal, even with former enemies, in the quest for power and resources. In the dolphins' case the objective is to find temporary allies to 'win' females in the breeding season."Females, too, tend to develop their own long-term partnerships. Those that are pregnant or with calves of similar age tend to stay together."Being one of the few sheltered areas on the Western Australian coast Cockburn Sound is a haven for nursing dolphins.Mothers and young calves stay close to the eastern (mainland) shore of the Sound, moving north and south across the shipping lanes leading to and from the wharves serving the Kwinana industries.Sharks Why the nursing females prefer to stay close in-shore is not known for certain, but one reason could be that they are able to keep their young as far removed as possible from natural predators -- the main danger being sharks, which are in abundance on the west side of Garden Island.However, mortality remains high, with half the calf population lost (for various reasons) before weaning. Bec Donaldson also has evidence that some dolphin calves suffer agonising deaths when tangled in fishing lines.The long hours patrolling the waters of Cockburn Sound alone in all seasons have been richly rewarding for Bec Donaldson. The love for 'her' dolphins is apparent in her voice and, although she will personally take a break from the sea when she finishes her field work at the end of summer, her research has provided a sound foundation for other researchers to continue the work on the Sound residents.She says BP Kwinana management's foresight in sponsoring the four-year research project demonstrated the value of partnerships between industry and university research, and had provided new insights on one of nature's most charismatic animals.
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