Marine Biology

Ecology of the Beaked Whale



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Ecology of the Beaked Whale:

There is no one species in taxonomic classification that is referred to as a 'Beaked Whale'. That is to say that the term Beaked Whale refers to several types of whale that have shared characteristics, including appearance, feeding strategies and shared evolutionary DNA heritage.

Generally speaking, Beaked Whales look like oversized dolphins, and have relatively small pectoral fins, as well as the characteristic 'beak' giving the family 'Ziphidae' its name.
Some species are larger than others, but the common defining factors are the prominent 'beak' or protruding lip, the 'sucking' feeding strategy, and propensity to dive to the extreme depths of oceans (Burnie, 2001).

Taxonomic Classification:

The ecology of the Beaked Whale is an all-encompassing one as the family these whales belong to (classified as the Ziphidae family), comprise 21 different species, sub-divided into 6 different genera (Anon, 2008).

These include:

1) The Berardius genera or Giant Beaked Whales comprised of two species, which are Baird's Beaked Whale (Berardius bairdii) and Arnoux's Beaked Whale (Berardius arnuxii).

2) The Hyperoodon genera or Bottlenose Whales, which are also comprised by two species; namely the Northern Bottlenose Whale (Hyperoodon ampullatus) and the Southern Bottlenose Whale (Hyperoodon planifrons).

3) The Indopacetus genus, represented by one species, the Tropical Bottlenose Whale (Indopacetus pacificus).

4) The Mesoplodon or the 'Single-tusked' whales, which make up the bulk of the Beaked Whale family with 15 species, including True's Beaked Whale (Mesoplodon mirus) and the Ginkgo-toothed Beaked Whale (Mesoplodon ginkgodens) a species found in the tropical waters of the Pacific Ocean.

5) The Tasmacetus genus, which is represented by a single species, known as a Tasman Beaked Whale (Tasmacetus sherpherdi), and can be found in the colder temperate waters in the southern hemisphere. The Tasman is more like a giant Dolphin in appearance, and unusually for the family Ziphidae, it also has teeth.

6) The Ziphius genus is represented by its sole member, Cuvier's Beaked Whale (Ziphius cavirostris). This species has the most wide-ranging territory (from the far north Atlantic to Australia) and is thought to be one of the most abundant. It is characterised by its 'goose-like' snout that gives it its other name of the Goose-beak whale (Burnie, 2001). Other features include visible scars from skin parasites, and territorial scars (among males) which are the result of battles with other males over territory and females.

As we can see the classification and sub-division of these whales belies the complex nature of their individual ecology and distribution. Therefore it would be futile to explore the ecology of every species in a short article like this.

Here I will try to give an overview of the ecological aspects that the Beaked Whales share, using examples of specific species where applicable.

What is known about Beaked Whales at present?

Numbers and Distribution:

Beaked Whales are one of the most abundant taxonomic groups of mammals in the world, but among the least understood or studied. This is due to their somewhat unique life cycle and feeding habits, which force them to frequently occupy the depths of the ocean, normally out of reach to humans (Carwardine, 2000).

Due to the adaptive nature of Beaked Whales, they occupy most of the world's oceans, in both the northern and southern hemispheres. Exact numbers of each species are difficult to estimate due to their elusive behavior, but numbers are thought to be in the hundreds of thousands (or locally common) in species such as the Northern Bottlenose (Hyperoodon ampullatus).
Other species such as Longman's Beaked whale (Indopacetus pacificus), which is found in the pacific areas off Indonesia, are thought to be more endangered, and are fewer in number.


Special characteristics of Beaked Whales:

Like most other whale species, Beaked Whales, have 'collapsible' lungs that deflate almost completely when the whale reaches depths of 800 metres or more (Carwardine, 2000). This is because if they did not the whale would be crushed under its own weight, as oxygen becomes denser at these extreme depths (Burnie, 2001).

Beaked whales also have oxygen-enriched blood, which means more oxygen is attached to red blood cells being pumped around their body, and thus this enables them to dive further and for longer.

It is also believed that the Ziphidae family of whales has the densest bones of any species of animal in the world (Anon, 2008), when gauged pound for pound, even more so than the Blue Whale (Balaenoptera musculus) (Burnie, 2001).
Dense bones are very important when your food lives at depths of between 800 and 1,500 metres, and they allow the whale to overcome buoyancy and dive much more quickly.
They also help to overcome the colossal amount of pressure that affects the whale's bodies at great depth, where their bodies can weigh more than twice their usual weight (Burnie, 2001).

Beaked Whale species also have 13 stomachs. This is presumably to gain the maximum amount of nutrition from their food, as they expend vast amounts of anaerobic energy to metabolise and break down this food into energy. This energy is turn used to hunt for more food and breed.

A classifying feature of Beaked whales, which distinguishes them from Baleen whales (or filter feeders) is the presence of teeth. While these are not 'true teeth', when compared to the Killer Whale (Orcinus orca), they nonetheless categorise Beaked Whales among the Odontoceti or 'toothed' whales.

These teeth are thought to be used in conjunction with the tongue, to form a vacuum, whereby prey is 'sucked' into the mouth of the whale and eaten. More developed teeth, (usually two slightly elongated tusks in males) are thought to be used in a secondary role, as weapons to fight over females (Carwardine, 2000, Anon, 2008) as in Cuvier's beaked whale (Ziphius cavirostris).

Habitat:

Most Beaked whales are deep ocean dwellers, preferring the open expanses of the sea to the more sheltered coves of the shoreline. They frequent the areas around the convergence of continental shelves, and are also to be found in deep water canyons (Anon, 2008, Burnie, 2001, Carwardine, 2000), presumably as this is where their food is to be found.

Breeding and social behaviour:

Beaked whales tend to congregate in small groups of around 10 30 individuals of the same sex and similar age. Some species are highly sociable (Baird's beaked whale) while others are more solitary, particular adult male Cuvier's beaked whales (Ziphius cavirostris) and the Northern Bottlenose (Hyperoodon ampullatus) (Burnie, 2001).

Like most other whale species, gestation periods are relatively long and young calves stay with their mothers as part of a 'school' for up to five years after birth (Carwardine, 2000).

Diet and Feeding:

As oppose to their largely vegetarian baleen counterparts, beaked whales are all carnivores. However as they do not possess 'true teeth', that can be used for feeding, they suck their prey into their mouths.

This is thought to be achieved by manipulating the tongue via the throat muscles, to create a vacuum. In this way the pressure in side the whale's mouth becomes greater than that outside in the water, whereby the whale simply sucks in his dinner, rather like when you eat soup.

Species such as Baird's beaked whale (Berardius bairdii), will sift through seabed mud in this way and suck up, water, mud and all before sifting through the mixture to reach their prey. Afterward they expel the excess water and detritus (Burnie, 2001).

Generally, most beaked whales feed on squid species (with particular reference to Cranchiid and Histiotheuthid families) and large fish, at depths of between 200 and 2000 metres (Anon, 2008). It is thought other species like Arnoux's beaked whale (Berardius arnuxii) will also feed on crustaceans such as Cancrid crabs, which live on the deep-sea beds of the southern hemisphere.

Species of whale such as the Ginkgo-toothed Beaked Whale (Mesoplodon ginkgodens) are thought to feed on smaller prey (typically 10 20 cm in length and weighing less than 500g) (Anon, 2008) than the other beaked whale genera. This is probably the result of evolutionary competition , which reduces conflicts over feeding among species of different genera in confined areas of ocean. It may also explain why the Mesoplodon genera, to which the Gingko belongs, is the most abundant as it seems to be the most adaptable.

Conclusions:

The widespread distribution and diverse ecological features of Beaked Whales make them a valuable family, in terms of ecological research and the study of evolutionary adaptation.

These special features that are as yet not fully understood, are clearly the result of allopatric speciation, which is the divergence of similar characteristics over time from a common original species. Hence we can see the shared features of a protruding beak and small pectoral fins, occurring in species separated by thousands of miles of ocean.

The ever-widening expanse of man into the as yet under explored oceans of the world, means that these whales are in danger of becoming extinct without a true knowledge of their ecology ever being fully understood. The complex and delicate nature between the beaked whale predators and their prey, means that even slight changes via habitat destruction, over-fishing or a depletion of prey species could spell disaster for them.

As yet the conservation status of these whales is not yet known in many cases, and this fact may be both the greatest chance for their survival and the biggest factor likely to contribute to their decline.

Sources:

Burnie, D. (2001). Animals. Dorling Kindersley, London.

Carwardine, M. (2000). DK Handbook: Whales, Dolphins and Porpoises. Dorling Kindersley Publishers.

Anonymous. (2008). The Beaked Whale Resource. From http://www.beakedwhaleresource.com accessed 19/08/08.

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