Bottlenose whales are relatively large beaked whales ; „ (6-9 m), found in deep waters of the North Atlantic and southern ocean. They are excellent divers, capable of diving for over an hour, and routinely dive deeper than 800 m. Their primary prey is deep-water squid of the genus Gonatus, although some fish and benthic organisms are also consumed. Northern bottlenose whales are the best-studied beaked whale, with data from whaling records and a long-term study on live animals concentrated in a submarine canyon known as the Gully off Nova Scotia, Canada. Relatively little is known about the southern bottlenose whale. Individuals are found in small groups, ranging from 1 to 20. In the Gully population, males form long-term bonds, whereas females live in a loose network of associates. Northern bottlenose whales were heavily whaled from the 1850s to the 1970s and numbers are believed to be reduced throughout their range. Only a few southern bottlenose whales were harvested.
I. Description and Diagnostic Characteristics
Bottlenose or bottle-nosed whales are large, robust-beaked whales distinguished by their large bulbous forehead and short dolphin-like beak (Fig. 1). They are chocolate brown to yellow in color, being lighter on the flanks and belly. This coloration is believed to be caused by a thin diatom layer. Newborns are gray in color with dark eye patches and a light-colored forehead.
Figure 1 Spyhop of a northern bottlenose whale showing prominent beak and V-shaped throat grooves.
The maxillary crests of males become larger and heavier with age, leading to a change in the shape of the forehead, with mature males having a flat, squared-off forehead whereas female/immature males have a smooth-rounded forehead. The dense bone in the males forehead may be used for male-male competition, as males head butt one another. Males possess a single pair of conical teeth at the tip of the lower jaw; however, these teeth are rarely visible in live animals.
II. Distribution and Range
Northern bottlenose whales are found in cold and temperate waters of the North Atlantic, from the ice edge to the Azores, almost always in waters deeper than 500 m. They concentrate in submarine canyons, the shelf edge, and other areas of high relief. A resident year-round population is found in the Gully, a large submarine canyon off the coast of Nova Scotia, Canada. Whales found in different areas have different length distributions, indicating that there may be geographic isolation between the different whaling grounds. Preliminary analysis of mitochondrial DNA suggests that there may be reproductive isolation between bottlenose whales off Labrador and in the Gully.
Southern bottlenose whales are found throughout the southern hemisphere, from the ice edge to 30°S. There are no known areas of concentration, although relatively little effort has been made to identify these animals. Recent molecular work on southern bottlenose whales indicates that there may be more than one species (Dalebout et al, 1998). Many sightings of a large beaked whale in the tropical Pacific have been identified as a bottlenose whale and may represent a more tropical distribution of H. planifrons, or a third undescribed Hyperoodon species. Pitman et al. (1999) suggested that the tropical bottlenose whale is actually Longman s beaked whale Indopacetus pacifiais, known hitherto only from skeletal remains.
III. Ecology
Bottlenose whales are deep divers feeding predominantly on squid of the genus Gonatus, although other species of squid are eaten. Adult Gonatus are primarily benthic, although juveniles may inhabit the water column. Fish (including herring and redfish) and benthic invertebrates such as starfish and sea cucumbers are occasionally consumed. Time-depth recorders on two northern bottlenose whales in the Gully indicated that these whales were routinely diving to or near the sea floor, over 1400 m below the surface.
Evidence from whaling suggests that northern bottlenose whales migrate north in spring and south in the fall; however, evidence for this is weak and this migration may actually represent a migration of whaling vessels. Stomach contents of stranded animals indicate that both northern and southern bottlenose whales travel over long distances (ca, 1000 km), although it is not known if these movements are routine. Individuals routinely return to the Gully after spending time outside the canyon, and bottlenose whales are found in the Gully year round.
IV. Social Organization
Both northern and southern bottlenose whales are typically found in small groups (one to four individuals), although groups of up to 20 have been observed. Nothing is known about the social organization of southern bottlenose whales, and only the Gully population of northern bottlenose whales has been studied. In the Gully, individuals live in fision-fussion groups and most associations are brief (on the order of minutes to a few days). Females form a loose network of associates with most members of the community. However, mature males form long-term companionships with other mature males and these associations last for years. The function of these associations is unknown, but they may be linked to mating and may be similar to male coalitions in bottlenose dolphins.
V. Interactions with Humans
Northern bottlenose whales are often described as curious, as they will often approach boats. Whalers exploited this behavior to find groups of bottlenose whales, and as healthy whales would often remain near wounded individuals, the entire group was often captured.
The commercial hunt for northern bottlenose whales began in the 1850s and extended until the 1970s. Over 80.000 whales were captured during this period, and many more were harpooned but not recovered. Preexploitation numbers are estimated at 40-50,000 whales, although this number is at best a rough guess. There is no current estimate for the size of the North Atlantic population, but it is unlikely that it has fully recovered from whaling. Only 130 individuals reside in the Gully currently and this population is likely still recovering from the whaling catch of approximately 60 animals taken from the area in the 1960s.
The study in the Gully represents the first long-term study of live beaked whales. Crews from several documentary films and magazines have visited the Gully, as it is one of the few places where beaked whales can be observed routinely.
