THE DOWN UNDER DOLPHIN

Forest and Bird, Volume 18, Issue 4, 1 November 1987, Page 32

THE DOWN UNDER

DOLPHIN

by

and

Stephen Dawson

Elisabeth Slooten

Te world’s whales, dolphins and porpoises, 76 species in all, comprise some of the most fascinating animals on the planet. Shaped by a need to move ina viscous environment they all are similarly streamlined, but there are awesome differences in scale. Female blue whales, usually a little larger than the males, reach over 90 feet long, and are without doubt the largest animals ever to have lived on Earth. At the other end of the scale is Hector’s dolphin (Cephalorhynchus hectori). Adult Hector’s dolphins, usually less than four and a half feet long, are the world’s smallest oceanic dolphins. Most dolphins are capable of travelling large distances, and are widely distributed. Bottlenose dolphins, the species endeared to us through the television series ‘‘Flipper’’, occur in every ocean. Hector’s dolphin is one of the exceptions to this rule. The fascinating Cephalorhynchus genus comprises four species of small dolphins, each with a very.limited distribution and endemic to a different temperate coastal region in the Southern Hemisphere. Hector’s dolphin, named in honour of early New Zealand natural historian and surveyor Sir James Hector, is now one of the better known of this genus. We have been privileged to closely study this species, which is the only dolphin found solely within New Zealand waters. A survey of their distribution and abundance was the first step in a four-year study of Hector’s dolphin, and resulted in a total population estimate of 3000-4000 individuals. This is an extremely low figure for a marine mammal, and underscores the urgent need to discover more about the biology of this species. Several cetacean species listed as endangered number considerably more. Although sobering, the figure of 3000-4000 individuals has little meaning by itself. Some mammals, mice for example, could recover relatively easily from such a small population size, whereas elephants and others would face certain extinction. Having estimated the distribution and abundance of Hector’s dolphins, a comprehensive study of their social organization, reproductive biology and feeding ecology is now crucial to assess whether the species is as threatened as the population estimate would suggest. For the second phase of the study, we are working from a base on Banks Peninsula. Elisabeth is studying the behaviour and ecology of Hector’s dolphins while Steve is concentrating on their sounds and acoustic behaviour. The integrated approach to ani-

mal behaviour, co-ordinating both the acoustic and visual signals may provide unique insights into the mysteries of the social organisation, reproductive biology and conservation requirements of this remarkable dolphin. Behaviour To enable behavioural study our first task was to work out the behavioural repertoire of Hector’s dolphins. The list of observed behaviours grew steadily during the first summer and winter of the study, and has now reached the stage where only extremely rare behaviours could be still missing. The dolphins show a wide range of behaviours including a number of different postures, gentle and occasionally aggressive body contacts, bubble blowing, leaping, lobtailing, ‘‘spyhopping"’, surfing and playing with pieces of seaweed and other objects. Aggression in Hector’s dolphins is rare, and it appears that direct approaches, displacements and open-mouth displays usually avert more obvious aggression such as biting, forceful body contact, and hitting with the tail. Aggression is always one-way. We have yet to see an aggressive display that develops into a fight, where the recipient of a bite turns and retaliates against the original aggressor. While lobtailing, a dolphin hits the tail flat onto the water surface while swimming either normal way up or upside down. This movement is vigorous, makes a lot of noise and splash, and is usually repeated several times. Commonly seen in many dolphin species, lobtailing is thought to indicate excitement and in some situations possibly annoyance, usually in a social context — we have never seen lobtailing from a lone dolphin. During upside-down lobtailing (the most common type) it is usually possible to sex the individual, and, interestingly, virtually all of the Hector’s dolphins we have observed doing this have been males. Unlike Dusky and Spinner dolphins, Hector’s dolphins are not known for their spectacular acrobatics, but they do jump. When moving at speed, especially while bowriding or ‘‘racing"’ boats, they often make low, arching leaps, while at other times their jumps are usually more vertical. Almost invariably they re-enter the water head first, cleanly, with little splash. Only rarely do jumping Hector’s dolphins fall back into the water on their sides, although when this type of jump occurs it is usually repeated many times, always falling back on the same side. These ‘‘noisy’’, repeated jumps

may have social importance, but we get the impression that the dolphin may be ‘‘itching’’ itself. Most have tiny flattened whale lice scattered over their skin. These forage on the perpetually sloughing outer skin layer and although they appear to do no damage, probably cause some annoyance. Fastened on to the skin with tiny hooked claws, some of the lice may be dislodged by sudden, vigorous splashes. Some types of jumps are clearly social, and often one individual leaping seems to trigger others to follow suit. A disproportionate number of leaps are of two dolphins at a time, usually one leaping just a fraction of a second later than the other. This suggests either that the same stimulus causes both dolphins to leap, or that the leaping dolphin stimulates others nearby to doing likewise. Either way, we have found leaping is more common during courtship and other close social situations — such as just after two groups have come together. In fact, the meeting of two or more groups of Hector’s dolphins tends to cause a marked increase in activity in general. Group Associations In regions where they are relatively common, it is usual to find several groups of Hector’s dolphins in close proximity, say within an area of half to one nautical mile in diameter. Individual groups usually consist of two to eight dolphins, but there may be 50 or even a hundred dolphins in the general area. When a boat appears on the scene, or when one of the small groups starts to feed, often they will be joined by other groups. This is particularly obvious when the interactions of boats and dolphins are observed from a clifftop vantage point. The mingling of individuals from previously separate groups almost always results in a marked increase in activity. Individual dolphins closely approach one another more frequently, sometimes groups of three to five individuals mingle very closely for several minutes, frequently touching. Jumping, lobtailing, bubble-blowing, body contacts, and displacements all are more common when two or more groups have just come together, beyond what would be expected from the simple increase in number of dolphins present. Such group mingling invites a whole range of intriguing questions regarding which is ‘‘the group’’. Are the smaller units stable, perhaps family groups; or is it the larger aggregations which are of most biological importance, with the composition of

the smaller groups changing from day to day? Do males and females form separate groups? Our observations are helping to answer these questions, and an ongoing pho-tographic-identification programme is the key to it. Individuals can be recognised from photographs taken from the boat, making it possible to follow the movements and associations of individual dolphins. Observations on shorter-term group movements from clifftop observation sites help complete the picture. Most groups are of mixed sexes and sizes, and the only sexual segregation we see occurs only occasionally, in groups which are comprised mostly of mothers and young calves. As to the stability of groups, it appears that the small groups are quite flexible, but we need more data to be sure. Reproduction Newborn dolphins start to appear in the late spring month of November, and births occur over about three months into March. The newborns are 60-75cm long, about half the length of the mother, and are a darker grey than the adults. A series of light bands overlies the darker pigmentation which fades over the months following birth. Six months after birth the grey has faded to the adult hue, and the bands have disappeared. In the weeks following birth the calf is usually seen in very close proximity to its mother, almost as if they were glued together. As time passes the calf becomes more independent, and by six months is supplementing its mother’s milk with solid food such as squid. Sounds Our work with the sounds of this animal is in its early days, but we now have many tapes awaiting detailed analysis. Unlike other dolphins they make very few sounds that are audible to us, and make none of the squeals and whistle noises so often heard from Bottlenose dolphins. Most of the sound we have analysed so far have been sequences of high frequency clicks, each click around 1/5000th of a second long, and extending far beyond the range of human hearing. Our ears have a range of

20Hz to 20,000Hz when we are young, and this response declines with increasing age. Most of the energy in Hector’s dolphin clicks is concentrated around 128,000Hz. Very sophisticated equipment is required to record these high frequencies. Sounds are picked up by a tiny high-frequency hydrophone (underwater microphone), boosted by a special amplifier and then fed into a tape recorder that gobbles tape at five feet per second. By comparison a standard cassette recorder uses tape at 1.875 inches per second. A commentary of the behaviour of the dolphins is recorded on another of the recorder’s four channels. The short clicks are used in echolocation, that is, the dolphins emit a click and listen for the returning echo. From the time delay of the echo, they can tell how far away the object is. This is the principle behind all sonar (Sound Navigation and Ranging) systems. Hector’s dolphins apparently do not emit another click until the echo of the first is received, thus as a dolphin approaches an object the click rate increases as the dolphin gets closer. Dolphins can discriminate between similar objects using echolocation, although precisely how they do it is not yet understood. Just what other information a dolphin can gain from the echoes is poorly know, and their significance to communication between individuals is the stuff of further study. The Future for Hector’s dolphins The threats to the continued survival of Hector’s dolphins are several. Probably the greatest threat is from accidental entanglement in coastal gill nets. Made from nylon monofilament, the nets seem to be invisible to the dolphin’s sonar. One navigational blunder and they are snagged, unable to reverse out. Caught with net around the snout, flippers and dorsal fins, they panic and drown. Gill netting around New Zealand is currently declining, but in the Banks Peninsula area kills between 10-15 percent of the local Hector’s dolphin population each year. That ‘‘incidental’"’ kill is probably worst around Banks Peninsula where dolphins and gill netting combine to disastrous

effect. There are natural predators also. SevenGill sharks are known predators, one caught recently had a whole dolphin head in its stomach, and five others caught the same day revealed dolphin remains also. Local fishermen claim to have found similar dolphin remains in blue sharks. Both these sharks are seasonally very abundant off parts of the New Zealand coast. As everywhere there are sublethal factors that may influence the dolphins. Like many countries, New Zealand's coastal fish resources have been overfished and the stocks of some species appear to be severely depleted. While it is not possible to assess whether this depletion limits Hector’s dolphin populations, it would be difficult to argue that the dolphins remain unaffected. Also unassessed as to their importance are the contaminants that are routinely found in samples of Hector’s dolphin tissue. In general, heavy metal levels are low, but the levels of DDT and PCB contamination gives cause for concern. Now is the time to act before Hector’s dolphin crosses the unseen boundary between threatened and endangered. Conservation should perhaps be seen not as the preservation of endangered species (though that is obviously important) but as the prevention of species becoming endangered. Most conservation action taken on rare species seems analogous to parking an ambulance at the bottom of a cliff. What we are trying to do here is to fence off the cliff. y& Acknowledgements A study like this is not possible without financial support. We are very grateful for grants from the Royal Forest and Bird Protection Society, the New Zealand Lottery Board, Project Jonah (NZ), World Wide Fund for Nature (NZ), Cetacean Society International, Pacific Whale Foundation, IBM (NZ), Oceans Society (NZ), and New Zealand Underwater Association. Neptune Aquasuits, Hutchwilco, and Neill, Cropper and Co., sponsored their equipment for the study. Racal Electronics, Bruel and Kjaer, David Reid Electronics, Tait Electronics and Anthoni Computer Automations Consulting Ltd have generously lent equipment for our use.