Mysticeti

Introduction

There are four families of baleen whales, the Balaenidae, Neobalaenidae, Eschrichtidae and the Balaenopteridae. However, the exact number of species as well as the phylogenetic relationships between these species has been a matter of hot debate for several decades. Despite extensive research, especially in the last twenty years, the phylogenetic relationships among the Mysticeti still remain uncertain. Morphological and molecular approaches have often generated conflicting arrangements. Studies based on morphological analyses have generally produced limited insights into phylogenetic relationships. This is largely because of the challenges their large body size, oceanic distribution, and highly derived morphological characters create for cladistic analysis. Both molecular and morphological analyses generally agreed that the family Balaenidae are the most basal extant baleen whales, followed by the Neobalaenidae, the pygmy right whales. However, uncertainty remained over the position of the Eschrichtiidae (the gray whale) and the relationships of the species within the Balaenopteridae. However, this by no means represents the final or definite picture. As research persists, scientists are finding what they believe to be new species and continuing studies based on different molecular data produce varying results. Thus, some recent studies suggest revision of the relationships suggested above may be necessary.

Recent advances in molecular phylogenetics have begun to shed light on the unresolved issues. Two molecular studies based on complete mtDNA sequences and short interspersed repetitive element (SINE) insertion data provide a clearer picture of the phylogenetic relationships among the extant mysticetes. The diagram below represents the phylogenetic relationships of the baleen whales uncovered using the combined results of these two studies.

Phylogenetic tree of the mysticetes. Tree by Peter Tomiak and Felix G. Marx, University of Bristol. Pictures of cetaceans taken from Wikipedia

Diversity of Mysticetes

Family Balaenidae

• Bowhead Whale (Balaena mysticetus)
  
  Two bowhead whales. U. S. National Oceanic & Atmospheric Administration (NOAA)
  
  Length: 14-16m
  Weight: 60,000 – 90,000kg
  Distribution: The bowhead whales have an exclusively northern hemisphere circumpolar distribution and are the only baleen whales to remain in arctic waters all year round. In the eastern Arctic there are thought to be three subpopulations; the Hudson Stock, the Davis Strait stock and the Spitsbergen stock. The western Arctic populations inhabits the Beaufort, Bering and Chukchi Seas and appear to be of the same stock. There is also an isolated stock in the Sea of Okhotsk. In spring they migrate northwards following gaps in the pack ice.
  Diet: Mainly copepods and euphausiids (kriss) though a significant number of epibenthic organisms are included
  General: The bowhead whale has a robust, stocky body which lacks a dorsal fin. It has the longest baleen plates of all mysticetes, exceeding 3 meters in length and as a result has a curved rostrum (upper jaw). They also have the thickest blubber of any extant animal, lack throat grooves and an extremely large head, which may make up as much as 40% of the entire body length. They are slow breeders, but evidence suggest that they may be extremely long lived, and can reach over 100 years of age. Bowhead whale populations have suffered dramatic declines due to commercial whaling.
• Northern and Southern Right Whales (Eubalaena glacialis/australis)
  
  Northern right whales with obvious callosities. U. S. National Oceanic & Atmospheric Administration (NOAA)
  
  Length: 11-18m
  Weight: 30,000 - 75,000kg
  Distribution: Right whales are found in temperate oceans worldwide. The northern right whale can be found in the Northern Atlantic and the Northern Pacific. The southern right whale can be found in all areas of the southern hemisphere oceans where moderate temperatures prevail. It is thought that the warmer waters of the equatorial region form a barrier preventing the northern and southern species mixing. Both species generally stay within close proximity to the continental shelves which offer their preferred food in abundance.
  Diet: Both are exclusively planktivorous feed mainly on copepods though the Northern right whale also feeds on krill.
  General: Right whales are closely related to the Bowhead whale, and share with it many physical characteristics. Like the bowhead, the right whales lack a dorsal fin and also have a long arching rostrum (upper jaw). However, they are distinguishable by by patches of thickened skin called “callosities” that form on the head region. These arise naturall and are present even in late-term whale fetuses, though colonies of whale lice or cyamids living within often harden them and make them more jagged with time. Sailors used to refer to the largest patch found on ths snout as the “bonnet”. The purpose of these callosities is unknown. However, they are larger in males than females and males have been observed stratching other males with their callosities, so it is thouht that they may play a role in sexual seletion. There has been debate as to whether a third species of right whale exists. Some scientists have suggested that the northern right whales should be divided into two species, the Atlantic Northern Right Whale (Eubalaena glacialis) and the Pacific Northern Right Whale (Eubalaena japonica).

Family Neobalaenidae

• Pygmy Right Whale (Caperea marginata)
  
  Length: 5.5-6.5m
  Weight: 3000-4000kg
  Distribution: Pygmy right whales are only found in the southern hemisphere, thought their exact range is unknown.
  Diet: Zooplankton.
  General: The pygmy right whale is the smallest of all the baleen whales. It has a prominent dorsal fin and small rounded flippers located on the underside of the body. Due to its small size and solitary life style, little is known about this species.

Family Eschrichtidae

• Gray Whale (Eschrichtius robustus)
  
  A gray whale surfacing. U. S. National Oceanic & Atmospheric Administration (NOAA)
  
  Length: 12-15m
  Weight: 27,000-36,300kg
  Distribution: There are two populations of gray whale. One migrates along the Eastern coast of the USA between Alaska and Baja California/Mexico, the other between the sea of Okhotsk and southern Korea. They live in coastal waters, usually no more than 100m deep.
  Diet:The gray whale filters out benthic invertebrates (inlcuding amphipod and isopod crustaceans, polychaete worms and mollusces) and small fish within the top few layers of sediment on the ocean floor (see feeding section).
  General: Gray whales are the most coastal of the baleen whales often found within 1km of the shore meaning they are among the best studied cetaceans. Gray whales do not have a dorsal fin, but have a series of ridges on the back. This whale is one of the most heavily parasitized. Parasites, such as barnacles and whale lice (cyamids) create large yellow/white patches on the skin of gray whales, especially aroudn the top of the head. Migration in these whales has been well studied. They usually travel in a steady fashion at approximately 8km/h surfacing every 3-4 minutes. During their migration the gray whales are seen “spy-hopping”, in which the whales head protrudes from the surface ot survey its surroundings. It is though that this may allow the whale to view the adjacent shore and thus orient their migration.

Family Balaenopteridae ('Rorquals')

• Bryde's Whale (Balaenoptera brydei)
  
  Length: 11.5 – 14.5m
  Weight: 10,000 – 20,000kg
  Distribution: Bryde’s whales inhabit subtropical and tropical waters and prefer coastal, rather than deeper waters.
  Diet: They feed mainly upon fishes in schools, for example, sardines, though crustaceans and squid are also consumed.
  General: Bryde’s whale are relatively small and poorly studied. A small curved dorsal fin is present and although very similar to the sei whale, can be distinguished by three parallel ridges on the head, extending from the blow holes to the jaw, while the sie whale has only one. Much taxonomic uncertainty surrounds the group. There is still confusion as to whether there is more than a single species of Bryde’s whale. Several scientists believe that the pygmy brides whale, Balaenoptera edeni represents a separate species. Further to this, in 2003, based on molecular evidence, a new species of Bryde’s whale was reported in the journal Nature (Wada et al. 2003). This new species is known as Omura's Whale, Balaenoptera omurai, though virtually nothing is yet known about this creature (even the study that concluded it to be a new species was based on a whale carcass washed onto the shore of a Japanese island in 1998). A recent study in 2006 presented data suggesting that B. omurai evolved as an ancient independent lineage that diverged much earlier than B. brydei and B. edeni. Some scientists are yet to be convinced however, and claim that further DNA must be analysed before its status can be confirmed.
• Sei Whale (Balaenoptera borealis)
  
  Length: 12-15m
  Weight: 15,000-22,000kg
  Distribution: Found in all the world’s major oceans, but prefers deep off-shore waters, and only rarely in polar and tropical waters.
  Diet: Zooplankton but also small fish such as pollack, anchovies, herring, cod and sardines.
  General: After the blue and fin whale, the sei whale is the third largest baleen mysticete. It is dark gray with a white chin, throat and belly and also has a pointed snout and a tall sickle shaped dorsal fin. The whale is often confused with Bryde’s whale without close inspection due to its physical similarity. While diving to only shallow depths, the Sei whale is the fastest baleen whale, capable of reaching speeds of nearly 50 kilometres per hour.
• Blue whale (Balaenoptera musculus)
  
  A blue whale. U. S. National Oceanic & Atmospheric Administration (NOAA)
  
  Length: 24-27m (though specimens of nearly 34m have been found)
  
  Weight: 150,000kg+, up to 180,000 - 190,000kg
  Distribution: The blue whales occur in all oceans and in a variety of habitats. There are thought to be three subspecies of blue whale each occupying a different range. The northern blue whale (B. musculus musculus) inhabits the Northern Atlantic and Pacific, the southern blue whale (B. musculus indica or B. musculus intermedia) the southern hemisphere and the pygmy blue whale (B. musculus brevicuada) the southern Indian ocean and South Pacific.
  Diet: Blue whales are considered the ony rorqual that are not generalists. It subsists almost entirely on krill (euphausiids).
  General: The blue whale is the best known of the baleen whales because of its large size. It is probably the largest animal ever to have lived on this planet. Blue whales have a large ridge on the head from the snout to the blowhole and a very small dorsal fin. They communicate using very low frequency, long wavelength sounds that can propagate great distances under water. The population structure of blue whales is complex, and it is unclear how migratory behavior varies of different sex or age classes. Indeed, generally knowledge of populations of the blue whale is severely limited by their lack of accessibility for research, The pygmy blue whale is much smaller than the other two subspecies, but evidence suggests, it occupies a similar niche.
• Fin Whale (Balaenoptera physalus)
  
  A pair of fin whales. Photo taken by J. Waite, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Alaska Fisheries Science Center, National Marine Mammal Laboratory
  
  Length: 18-27m
  Weight: 30,000-75,000kg
  Distribution: These are found in ocean worldwide, though these cetaceans prefer deep water.
  Diet: Mostly small crustaceans, though fish such as mackerel and herring are also usually part of the diet.
  General: The fin whale is a quick swimmer capable of speeds up to 40kmph. It has a thin slender physical appearance with a large dorsal fin which is located far back on the body. Studies have shown that the fin whale is capable of diving up to 470m, the greatest depth for any mysticete.
• Humpback Whale (Megaptera novaeangliae)
  
  A humpback whale breaching teh surface. By J. Waite, U. S. National Oceanic & Atmospheric Administration (NOAA)
  
  Length: 12 - 19m
  Weight: 30,000 - 48,000kg
  Distribution: Humpback whales have a worldwide distribution, though follow fixed migration patterns spending winter months in tropical or subtropical waters, and summer months in the cooler polar waters. There are three main populations in the North Pacific, North Atlantic and southern hemisphere.
  Diet: Small schooling fish and plankton.
  General: Humpbacks have long front flippers. Male humpback produce elaborate songs and are also known for “breaching” (where the whale leaps from the water) and their strange feeding habits involving the production of “bubble-nets”.
• Northern Minke Whale and Antarctic Minke Whales (Balaenoptera acutorostrata/bonae-rensis)
  
  Length: 7 – 10m
  Weight: 4,500 to 9,000kg
  Distribution: Found in oceans worldwide, but favour temperate waters.
  Diet: Minke whales will feed on zooplankton, but mostly eat fish that swim in shoals, such as cod.
  General: Within the order Mysteciti, only the pygmy right whale are smaller than the minke whales. Minke whales have pointed snouts and a distinct curved dorsal fin. They have a dark colouration but northern mink whales have easily recognisable white bands on their flippers. There is also a dwarf minke whale growing to a maximum length of 8m, which may represent a subspecies of Balaenoptera acutorostrata.

Feeding and Baleen

Three segmenta of baleen plate. Photo by Peter Tomiak, University of Bristol

Most baleen whales feed intensively in productive, usually high latitude waters during a four to six month period in the summer, while the remainder of the year is spent travelling and breeding. It is estimated that during these feeding seasons, large baleen whales eat around 4% of their body weight each day. As a result, food intake reaches above the daily required amount, and the excess is stored as blubber. For example, blubber can make up 27% of the blue whales body weight and is a vital energy store which sustains the whale during the winter months. Although teeth may be present during the embryonal phase, baleen whales are distinguished by the replacement of teeth by baleen plates which are attached to the upper jaw and used for filter feeding. These plates, derived from the dermal tissue are actually composed of thin individual bristles Baleen continues to grow throughout the lifetime of the whale and is made of keratin, a fibrous protein, while hydroxyapatite is also present in the baleen of most mysticetes.

There are two mechanisms by which different species do this. The bowhead whale and the right whale are “continuous suspension feeders”. These whales swim with their mouths continuously open, taking in water through a opening between the rows of baleen at the front, and straining zooplankton, such as copepods and krill as water leaves through their fine baleen. Other whales, including the members of the Balaenopteridae are “intermittent ram suspension feeders”. These will intermittently gulp enormous mouthfuls of water containing prey. Once the mouth is closed they raise their tongue towards the palette to create internal pressure, and force water out through the baleen plates. The zooplankton trapped on the baleen plates is then subsequently swallowed. In the blue and fin whales, the lower mouth, or ventral pouch, expands as the mouth opens, allowing as much as 70 tonnes of water to enter. Parallel grooves running on the lower mouth enables this expansion (the name “rorqual” is Norwegian meaning “furrow whale”. These rorquals generally consume larger prey including squids and small fishes as well as the smaller zooplankton.

A bubble net produced by a feeding humpback whale. Photo taken by J. Olson, Source - National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Alaska Fisheries Science Center, National Marine Mammal Laboratory.

Gray whales have a slightly different method of feeding. These feed mostly along the ocean bottom, rolling onto their side and sucking in water and sediment laden with abundant invertebrates which are trapped by the baleen as the water and mud is expelled. They are the only baleen whales to employ such a strategy. When feeding they leave pits or bites in the ocean floor. Humpback whales also show a unique feeding method. After diving, they slowly circle to wards the surface and whilst doing so, blow bubbles upwards. These bubbles produce a visual barrier to fish above which become caught in a “bubble-net”. The humpback then ascends with an open mouth, gulping up the clusters of fish. Sometimes the ring of bubbles reach up to 30m in diameter, and often the creation of the bubble-nets involves a dozen whales in cooperation.

The Skull of Baleen Whales

The skull of the baleen whales exhibits extreme modifications, more so than in the toothed whales. The main modifications include the extension of the jaws (the upper of which supports the baleen plates and is called rostrum), forward movement of the supraoccipital (the back of the skull) region over the frontal, and the merging of the rostral and cranial bones as a consequence. The different species of the Mysticeti show modifications to the basic plan. For example in species with long baleen, such as the bowhead whale, the rostrm is curved to accommodate for the extra length of these feeding structures. In the bottom-feeding gray whale on the other hand, the jaws are shorter and thicker jaws than in other species with short stiff baleen.

Size and Age

The baleen whales are generally larger than the toothed whales, although there is large variation within the mysticetes. For example, an adult pygmy right whale is usually between 4-6.5m in length, while blue whales have an average length of about 21m but can exceed 30m. Female baleen whales are generally larger than males. So what are the advantages of evolving to be of such large size? Whales are endotherms, and retention of body heat is greater in animals of large size due to a decrease surface area to volume ratio. Also heat loss is prevented as large body size allows thick layers of fat (blubber). In the bowhead whale this can be up to 50cm thick. Also since oxygen storage capacity increases in proportion to body mass, larger whales can store more oxygen both in absolute terms, and relative to their rate of oxygen use, enabling whales to dive so deep. Large size also means a decreased risk of predation. The age of whales can be determined because the earplug consists of layers, which are visible when the plug is dissected. It has been discovered that one growth layers is formed each year allowing the age of the whale to be calculated. Through such means it has been found that fin whales may live for up to 90 years.

Bioacoustics

Unlike members of the Odontoceti, baleen whales do not echolocate. However, baleen whales do communicate to attract mates, repel rivals, communicate within a social group. Different mysticete species use a variety of different types of noise including singing, short pulses, and low frequency moans capable of travelling great distances. For example, the humpback whale Megaptera novaeangliae produces complicated “songs”. Song learning is a special case of vocal learning, and vocal learning can be viewed as a special kind of imitation. The songs the humpbacks produce lie within a 30-8000Hz range, and usually vary between 7-15 minutes in duration before being repeated (a cycle which may last up to 22 hours). Studies throughout the last two decades have shown that humpbacks appear to copy features of songs they are exposed to, and may copy entire songs. However, unlike singing birds, humpbacks modify their songs annually, never becoming settled on a particular song structure or repertoire. It appears that populations of humpbacks in different regions share the same song, though it is normally only males that produce them, usually whilst in the winter breeding grounds. Although the reasons for these elaborate songs are yet to be fully understood, it is most likely that they are used to mark their territory, warding off other males, and attract female whales.

Please click on the sound spectrograms below in order to listen to the recordings:

Several individual call of humpback whales. © Cornell Lab of Ornithology, Bioacoustics Research Program, used with permission.

On the other hand, the blue whale produces very loud low pitch (12-390Hz), long wavelength moans which can carry further than any other animal sounds known and be detected over a thousand miles away.

Because the sound a blue whale produces is so low, the recording has been speeded up ten times in order to make it clearly audible. There are three parts to this sound: a series of clicks (trill), followed by three moan-like repetitions. © Cornell Lab of Ornithology, Bioacoustics Research Program, used with permission.

Right whales also make low-frequency sounds (in the 50-500Hz range), and studies have revealed that they have at least two types of call; contact calls when individuals are widely separated, and calls used by females to attract mates.

Moans uttered by a female southern right whale calles 'Archipelago'. © Cornell Lab of Ornithology, Bioacoustics Research Program, used with permission.

Other whales such as the mink whales produce very rapid sequences of short pulses, in the frequency range of 30 to 450 Hz. Each pulse only lasts 100-200 msec. The finback whale also produces combinations of pulses, often occur in deliberate, patterned sequences which can be repeated for many days on end.

This recording has been speeded up ten times, which has also raised the pitch by about three octaves. © Cornell Lab of Ornithology, Bioacoustics Research Program, used with permission.

It was actually because of the hostility between the superpowers during the Cold War that the extensive recording of whale sounds developed. The US Navy installed hydrophones in the oceans to track the movement of Soviet submarines. The system, known as SOSUS (Sound Surveillance System) was declassified in the 1990’s and made available to biologists, who have used them to record the sounds created by whales. Recently, research has been undertaken in an attempt to assess the disruption of the behaviour of whales due to the creation of anthropogenic noise. It is feared that noises produced by shipping, oil drilling and scientific studies (for example to map the ocean floor) may be altering the normal behaviour and communication of baleen whales. A recent study analysed the effects of exposure to loud noises on marine mammals and observed responses, including startle and fright, avoidance, and changes in behaviour and vocalization patterns in baleen whales. Changes in behaviour could subsequently lead to lower reproductive success in individuals, though presently the effects of this interference on the population and social structure of marine mammals are still largely unknown.

Breathing and Diving

Although whales live underwater, they are still air-breathing mammals and they show several adaptations to such a lifestyle. When breathing, baleen whales exchange almost the entire air volume in the lungs, making breathing very efficient (for example humans exchange slightly more than 12% of the lung volume). Also whales can retain a greater amount of oxygen in the mussels than can land mammals. Also in all extant whales, including the mysticetes, the bones of the top of the snout, the premaxilla, maxilla and nasal, have moved up and over the top of the skull independently in each clade; a good example of convergent evolution. This occurred due to the backward movement of the nostrils, which in whales becomes the “blowhole”, which lies above the eyes at top of the head. This is an adaptation enabling efficient breathing at the surface and the blowholes are closed by strong muscular flaps which are only opened when the whale breathes at the surface. Baleen whales have a double-blowhole while toothed whales only have a single blowhole.

Baleen whales can dive to great depths. This is aided by greatly reducing the heart rate, and limiting the blood flow, and thus oxygen flow to vital organs such as the heart and brain. In the past, diving depth data were inferred from whales that had been harpooned, echosounder datal and assumptions based on depth distributions of their typical prey species. However, a study in 1999 investigated diving depths in baleen whales using an electronic tag, recorded the maximum depths ever directly registered for any mysticete, by the fin whale which reached 470m (Panigada 1999). However the depth of diving is linked to the diet of the whale and availability of food, and diving to such great depths is rarely necessary, with most food occurring nearer the surface. However, baleen whales are considered to be shallow divers compared to some toothed whales such as the sperm whale which can reach depths of 3000m.

Locomotion

The tail flke of a humpback whale. Photo taken by J. Waite, National Oceanic and Atmospheric Administration.

Powerful tail flukes, held at the end of the tail, move vertically to propel baleen whales through the water. Baleen whales all show some variation around a characteristic streamline “torpedo-shape”. Modifications to this body form have arisen corresponding to the species life style:

• Blue whales – these have flippers and flukes adapted for fast efficient cruising in the open ocean.
• Right whales – these have a stocky body and flukes for efficient slow speed cruising which is useful for their continuous filter feeding lifestyle.
• Humpback whales – have flippers and a tail designed for rapid acceleration and high-speed manoeuvering which would help them catch the schooling fish on which they prey
• Gray whales - have flippers and flukes for optimal low-speed maneuvering, an adaptation to the coastal water habitats which they inhabit.

Migration

The distribution of gray whales. Diagram by Peter Tomiak, University of Bristol.

Most living Mysticeti species are migratory and tend to follow the same basic migratory pattern. In autumn they begin to migrate, so that the winter months which constitute the breeding season, are spent in the warmer low latitude waters. Summer months are spent feeding in the more productive, cooler waters of higher latitudes. It is thought that the underlying reason for mysticete migration is that for whale calves, energy conserved in warm water during the first months of its life can be devoted to growth and development. A developmental advantage over those born in cold water can translate into larger size in adulthood, and consequently higher reproductive success. (Clapham 2001). Other factors which may cause migration as well have also been sited, for example, “the predation hypothesis” which suggests killer whales which often prey on baleens have a lower frequency in low latitudes (Corkeron and Connor 1999). This season-dependent migration can be demonstrated by the gray whale, which has the longest migratory route of all mammals. It spends summer months in the Bering Sea and Arctic Ocean but in winter months, migrates to the warmer coasts off Baja California and off Korea and Japan. This one-way leg of the journey can reach 10,000km, and individuals may swim as far as 20,400km annually. Such migratory routes are well known following extensive study, and are often exploited for whale-watching.

Our knowledge about the migration of humpbacks has also increased in recent years because of genetic based research and satellite tracking of electronically tagged individuals. For example, one population of humpbacks migrate to Alaskan waters for the summer months and spend the following winter period in waters just off Hawaii. Exactly how the whales are able to consistently follow these paths without become lost still remains to be answered, though possible explanations include the use of ocean currents, physical features (the edge of the ocean shelf), temperature gradients and the earth’s magnetic field to find their way. Not all baleen whales migrate however, for example the bryde’s whale, bowhead whale and sei whale are all non-migratory.

The Impact of Man on Population Numbers

Evidence of whaling dates back to 6000BC. However, with time whaling techniques have become more sophisticated, and commercial whaling in recent centuries has been severely detrimental on baleen whale populations. The last century was certainly no exception and it is estimated more than 2 million whales were killed, in the Antarctic alone. It is only during recent decades that things have begun to change. The International Whaling Commission (IWC), a global international government convention, decided in 1982 that from 1986, commercial whaling should be suspended. Also, in 1983 the Convention on International Trade in Endangered Species of Fauna and Flora (CITES) listed most baleen whale species onto Appendix I and the remainder onto Appendix II. Limited trade is permitted for species listed under Appendix II, while Appendix I species cannot be traded internationally for commercial purposes. Some countries do continue to hunt whales. Japan uses a loophole to continue the killing under the convention’s provisions for scientific research, while Norway has also continued to exploit whales after filing an objection to the IWC moratorium decision. However, as a result of the work of IWC and CITES, as well as pressure from many animal rights campaigns, commercial whaling on the scale practised for most of this century appears to be a thing of the past. This is not to say that whaling is no longer a problem. Any reduction in population size will reduce genetic diversity, and leave populations more prone to stochastic (chance) events. Much heated debate continues about whether “sustainable” whaling is a feasible objective.

A recent study suggests that there are two threats currently that are significant at the population level. One is the entanglement of baleen whales in fishing gear. Although large mysticetes are often able to drag fishing nets away with them, a serious entanglement will often reduce the animal’s ability to feed and thus lead to a drawn out death from starvation. Coastal species that inhabit heavily fished regions, for example, the humpback and right whales off the eastern seaboard of the USA, are particularly vulnerable. The second threat to baleen whales at the population level the study suggested is ship strike. Another study found that in some areas, one third of all fin whale and right whale strandings appear to involve ship strikes. They found that ship strikes can significantly affect small populations of whales, such as the northern right whales in the Western Atlantic and suggest that measure to reduce vessel speed below a critical 14kn in areas of high incidence. In addition to these two more important factors, coastal habitat degradation and pollution, for example due to oil spills, are of potential concern for some of the smaller populations. The fin whale, minke whale, southern and Bryde’s whale are generally abundant throughout their range. The humpback and southern right whale, although previously heavily hunted, seem to have recovered. Of greater concern are many populations suffering from lower abundance. These include:

• Right whales (especially Northern right whales) – the right whales were probably the first whales to be commercial hunted on a systematic basis. They frequent coastal habitats, are slow movers, float once deceased, and consequently have been one of the prime targets for whaling, Also, especially among the northern right whales, whose range coincides with busy shipping lanes, many deaths are caused by collisions with ships. Now both species are listed under Appendix I of CITES and are listed in the Endangered Species Act. Although the southern right whale has also been heavily exploited by whaling, existing data indicates a strong recovery in most studied populations of these species. The northern right whale remains critically endangered throughout its range.
• Bowhead whales – Population numbers have declined principally due to commercial whaling and the bowhead whale is currently listed in the Endangered Species Act and on Appendix I of CITES. Particularly at risk are those found in the Okhotsk Sea (evidence suggest there are only a few hundred survivors) and several eastern Arctic populations. The bowhead whale of the North Atlantic had already been hunted to extinction.
• Western gray whales – When migrating, the gray whale comes in close proximity to the coastline making it an easy target for whaling in the past. For an unknown cause the gray whale became extinct in the North Atlantic within the past 200-300 years. Despite being reduced to perhaps only a few hundred individuals, the eastern gray whale population has made a full recovery after international protection in 1938. However, the western population remains very low at an estimated 250 animals. This is mainly due to continued hunting off the coasts of Korea.
• Blue whales - Being a relative fast moving species, the blue whale used to be a difficult target for whalers. However, technological developments in whaling have changed matters. The IWC estimates that from 1900-1995, 360,000 blue whales were killed in the Antarctic alone. There are currently no obvious threats today the blue whale. Thus it is thought that the failure of population numbers to recover in certain areas, could be a consequence of being reduced to a small population size.

Ecotourism is becoming increasingly popular. Whale watching offers a more sustainable way of commercially exploiting whales, while maintaining their numbers. In 1998, 9 million people participated in whale watching, producing an annual turnover of more than US$1 billion spread over 87 different countries and creating income for isolated small fishing towns, such as Kaikoura in New Zealand. As ecotourism grows, the financial worth of However, even this industry must be carefully managed to minimise risks to whales and the IWC has produced guidelines that should be followed. For example they suggest that the whales should be allowed to control the nature and duration of interactions, the boats should be designed to minimise damage in the case of collisions, and that there should be limits on the number of vessels and approach distances.