Tuatara: Volume 12, Issue 2, July 1964
Recent Observations in New Zealand Waters on Some Aspects of Behaviour of the Sperm Whale (Physeter macrocephalus)
Recent Observations in New Zealand Waters on Some Aspects of Behaviour of the Sperm Whale (Physeter macrocephalus)
The Sperm whale survey and marking programme which is currently being conducted by the Marine Department along the eastern seaboard of New Zealand has provided excellent opportunities to study some of the actions and reactions of this species, the largest of the Odontoceti.
Physeter macrocephalus is universal in distribution, being found in nearly all the large areas of open sea between latitudes 60 N. and 60 S. In the temperate and tropical parts of the Atlantic and Pacific Oceans it is often found in considerable numbers. Lesser concentrations are found in the Indian Ocean and the lower latitudes of the Southern Ocean. Sperm were hunted round the New Zealand coasts during the first sixty years of the last century; however the discovery of mineral oil sounded the death knell of the New England and Scots whalers who came to these waters.
In more recent years a few sperm whales which had ventured close inshore near the Tory Channel Whaling Station were taken and processed. They were not given serious consideration commercially until the collapse of the Group V humpback stock in 1962. on which the local industry had been based. The survey for sperm whales was instituted to investigate the numbers and movement of these animals to and from the Cook Strait region and adjacent areas that could be fished if the Tory Channel Company were to purchase a large steam chaser.
The sperm whale is perhaps the most interesting of the commercial whales, at least from the point of view of its distribution. The approximate geographical boundaries of the female population are between 40 N. and 40 S., but there is free movement of males outside these latitudes to colder waters. Each whaling season many thousands of sperm whales are caught south of 40 S. by the pelagic factory ships, and these are almost invariably males.page 107
Opinions differ on the reasons for this segregation, but on the basis of the available evidence the most likely explanation would appear to be connected with the polygamous behaviour of the species. The females are normally found swimming in harem ‘pods’ or schools in the breeding grounds of the tropics, sometimes with only a single male in attendance. It is assumed that the males which move down to the Antarctic are therefore those which are unable to take control of a harem and either leave the breeding herds or are driven from them. It is known that the males fight on occasions, using their great heads as weapons to butt one another. Nor is sexual segregation of the kind found in sperm whale populations unknown; one might draw a parallel with the breeding behaviour of the Elephant Seal. Nevertheless, the ‘surplus’ bull elephants stay around the harems so the parallel is not too exact.
All observations made so far in the course of the current survey have been on male sperm whales only. The sex of adult individuals is usually easy to distinguish, since the males are about 45 feet long on average, compared with the 35 feet length of the mature female. The male usually has a prominent dorsal hump above the pelvic region. Our present data indicate that the bulk of the population moving around the New Zealand coast are mature males.
(1) Methods of Observation
Observations on sperm whales have been made from both the sea and air. On numerous occasions it has been possible to watch individual whales for as much as an hour at a time. In February, 1963, a programme of whale marking was started, using launches of the Fisheries Protection Flotilla and locally chartered boats in selected areas. By the use of such vessels it has been possible to observe individual sperm whales from as little as twenty or thirty feet away.
Aerial observations on sperm whales have been confined more or less completely to occasions when the sea was calm and the surface wind slight or non-existent. When the surface is broken even to a small extent by spume and wave capping it becomes exceedingly difficult to pick out whale spouts from the air. In our experience it is possible to spot them from sea level in quite rough conditions, providing there is some sunlight on the water to give the spout contrast against the horizon.
(2) Movements at the Surface
Male sperm whales near the New Zealand coast have only rarely been observed travelling singly, although there is often a distance of several miles between individuals that are feeding.page 108
Our observations on feeding behaviour in sperm whales will be discussed in the next section. In the New Zealand area the males of this species usually travel in schools or pods of about six or seven individuals. In the Antarctic, however, pods of more than a hundred have been frequently observed, though these large aggregations seem to be rarer now than in years gone by.
It is not known how long these pods stay together, since it is all but impossible to track one for any length of time. By carrying out aerial transects we have been able to determine that pods may stay together for at least several days. This was noted in November, 1962, when advantage was taken of a week-long period of settled weather. Only one attempt to relocate a pod using launches on consecutive days has been successful so far.
In most temperate and sub-polar areas the movements of sperm whales seem to be closely related to their feeding habits, though this is not necessarily so in the tropics where the breeding grounds are. In the New Zealand area we have not so far noted northward movement at any time of year. It has been assumed by other workers that the sperm whales move down to the Antarctic waters in the summer and go north again in the autumn. Our own present data suggest that in some months the numbers of male sperm whales moving south is considerably reduced, but not that in those months there is a counter drift north. Some northward movement has been observed in a few areas round the coast, but upon closer investigation this has so far been shown to be local inshore movement or movement from one bank to another for feeding.
Northward movement may take place further out from the coast than we have so far been able to observe. No hard and fast conclusions on this kind of large scale geographical movement in the New Zealand area can be drawn until much more evidence is available.
The sperm whale travels along at about three or four knots when undisturbed, but its average speed over 24 hours may be much less. Slijper (1962) gives average speeds of about ten knots and observed speeds of twenty knots. In our experience an average speed of ten knots is far too high, and the figure of twenty knots sounds improbable for anything but possibly a wounded and panic-stricken bull. It would appear that Slijper was misinformed, or that the observers had confused species. However, there is little doubt that the sperm whale is capable of sprinting to ten or twelve knots on occasion, but it is not likely to sustain this speed for more than a few minutes.
When travelling undisturbed the bull sperm whale goes through a slow, shallow and dignified porpoising movement. At the upper part of the movement the top of the head and the blowhole page 109 are exposed, as well as the crest of the back as far as the dorsal ‘hump’. At the lower part of the movement the top of the dorsal hump may still be visible, or the body may be completely submerged for perhaps half a minute. This sequence is shown in Fig. 1.
The spouting rhythm of the undisturbed whale is regular, usually about once every 25-30 seconds. The beginning of the spout coincides with the front of the head breaking water, and finishes as the animal begins to sink under the surface again. The mist of the spout hangs for a second or so after the whale's head disappears.
The travelling whales are usually about a hundred yards to a quarter of a mile apart, but on several occasions two or more large males have been seen swimming along only ten or twenty feet from one another. As soon as a pod of whales reaches a suitable bank (or area of coastal shelf) and starts feeding, the pattern of movement tends to break up, and the whales move further apart.
(3) Feeding and Diving
The sperm whale is capable of very deep and sustained dives, and there are some fifteen cases on record of them found tangled in submarine cables from between 600 and 3,000 feet down. The normal food of the sperm whale is squid, which it searches out at depths of several hundred fathoms. Deep water fish such as groper and ling have been recorded in the stomachs of some of the sperm whales examined in the Cook Strait area. It is still not known whether the whale catches the squid on the bottom or in midwater. Nor is it known whether it searches actively for its food or waits passively with its mouth open.page 110
Some whalers believe that the white mouth of the sperm may luminesce in the twilight found at 500 feet and the almost complete darkness at even lower depths, luring the squid to it. This idea cannot be dismissed out of hand, since the very fact that the sperm nearly always surfaces close to the dive point indicates possible passive feeding.
The fact of sperm whales being found tangled in submarine cables is not a sure indication that the animal is a bottom feeder, since squid are normally pelagic. It is possible that when one of the sperm whales in question became tangled, it struck the cable at a point where it hung across a narrow submarine canyon or depression.
There is a difference of opinion as to whether the whale eats its prey at the point of capture or brings it to the surface first. Although we have sometimes observed albatrosses feeding on tentacles and other squid fragments in the immediate vicinity of feeding sperm whales, it seems most probable that the sperm usually swallows its prey whole at the point of capture. The fragments that we saw may have been the result of regurgitation.
Our own observations indicate that the average feeding dive (nearly always a deep one) lasts about fifty minutes, and the whale will almost invariably bring its flukes up vertically above the surface. A whale making such a deep dive is shown in Fig. 2. Whales about to dive deeply have been observed on occasions to ‘sprint’ for perhaps a hundred yards, presumably to gain additional momentum. When the sperm whale dives without bringing its flukes completely clear of the water, it will be making a shallow dive and will almost certainly surface again well within half an hour.
Sperm whales appear to surface in a porpoise fashion from both shallow dives and normal deep feeding dives, but on two occasions we have seen sperm whales breach vertically clear of the sea. They hung clear for a fraction of a second and then fell back with a splash that was audible two miles away. This breaching probably indicates that the whale has just completed an exceptionally deep or prolonged dive. The sequence of events is shown in Fig. 3.
Sperm whales that had surfaced after dives of threequarters of an hour were seen to lie at the surface and ‘pant’, spouting at intervals often less than ten seconds; their attitude giving the appearance of almost complete exhaustion. At such times the whales are easy to approach and will not again make a deep dive until they have been on the surface undisturbed for at least ten minutes.
(4) Reactions of Sperm Whales to Boats
If male sperm whales are chased after they have just completed a deep dive, as mentioned at the end of the last section, they page 111 will usually stay on the surface and either run straight or make a series of shallow porpoising dives.
When undisturbed sperm whales are approached closely by small boats their reactions are varied and interesting. Some sperm whales, particularly those appearing to be travelling steadily, will take little notice of an approaching boat, except to change course if it comes very close. This changing of course seems to be the usual reaction of sperm whales which have not been chased before. We discovered this to be true of whales approached by a boat with a slow-running engine, for example when the Fisheries Protection launches were used at half speed or slow speed.
Each time a whale was approached it would repeat the sequence of sinking slowly until it was about six or ten feet under the surface. It would remain like this until it was able to manoeuvre away from the launch. It would then come up and spout again.
We were unable to mark a single whale in this pod because of this behaviour, and although four marks were fired all were listed as misses. When two of these shots were made the target whales immediately went into shallow dives accompanied by violent flurrying of the flukes as the marks struck the water beside them. Whales which had been approached and marked on other occasions showed little or no reaction as the marks embedded in their back muscle. The reactions of the first-mentioned whales seem to indicate that they are very sensitive to sharp noises in the water, and that the shock wave generated by a mark hitting the water beside them arouses more alarm than a small projectile hitting them in the back.
We also noted the reactions of sperm whales approached by fast-moving boats. In some cases the whale would dive when the boat was still about half a mile away. A similar reaction was encountered in whales approached by boats with low-revving engines when we were certain that the whales in question had been chased before. The technique used when this happened was to reach the dive point, cut the engines and wait for the whale to surface again.page 113
Even more interesting observations were made on a number of isolated whales which had been feeding. One whale made a series of porpoising dives to avoid the launch and then sank into the water on its side, with the anterior end of the head, the tip of the left fluke and the tip of the left flipper clear of the water. From time to time as we circled the whale it lifted a considerable part of its head out of the water until the left eye could be seen.
A second whale, after being chased for some time, suddenly sank down until it hung vertically down under the water, with only the tip of its head to be seen bobbing about in the swell. Some whalers have told me that this reaction is quite commonly observed in the Antarctic, though I had not seen it before myself. These two attitudes are shown in Fig. 4.
Another bull sperm was spotted off the east coast of the South Island, moving southward and spouting normally. As we approached this whale, which was a large and solitary bull, it stopped spouting and began to move towards the boat with a considerable part of the head clear of the water.
This last whale behaved in a manner that we had not encountered in any other before. With stories of single ‘rogue’ bull sperm in mind we gave this whale a wide berth.
A brief outline of what is known of the distribution and sexual segregation of the sperm whale is given, along with a short history of the industry as it affected New Zealand.
The methods of observation used during the survey are outlined, together with a note on the weather conditions needed to spot sperm whale spouts successfully.
The group and individual movements of sperm whales are discussed.
The feeding and diving behaviour of male sperm whales are also discussed.page 114
Some observed reactions of male sperm whales to the close approach of boats are described.
Comments on these last reactions are not offered. Considerably more data has to be collected before this kind of behaviour can be evaluated.
Gaskin, D. E. Marine Dept. reports on the East Coast Sperm Whale Survey and unpublished data. 1962-63.
Perano, J. and G. Personal communications. 1962-63.
Slijper. E. J. Whales. Hutchinson Press. London. 1962.
These are due to the Perano Whaling Company, the New Zealand Navy, the New Zealand Air Force, the Civil Aviation Authority and many individuals too numerous to name. All these have given invaluable aid in this survey.