By Kim Gray, Wade Baker, and Brian Casey

The migratory patterns of Mysticetes have eluded scientific observers for years. Since the recorded history of whaling to the present day tracking by satellites, the pattern of mysticete movement across latitudes has been postulated and supported yet never proven. It has been assumed that mysticete whales use may environmental cues for navigation. These include sun and celestial orientation, benthic topography and coastal landmarks, water temperature, chemical traces or changes in the water and possibly biomagnetism. In order to have a better understanding of why some mysticetes migrate while others do not, the major features and characteristics between different families and species must first by examined. For simplification purposes, we have defined migrating mysticetes as those whales that move across 20° latitude and non-migrating mysticetes as those whales that move within a 20° latitude range.

There are many examples of migrating whales within the Suborder Mysticete. Migration patterns as well as the distribution of mysticetes has been classified into several different groups. The first type of migratory pattern is that of antitropical origin. Antitropical migration is defined as those whales that exist in a Southern Hemisphere and Northern Hemisphere stock. These two stocks have opposite migrations – as the Northern stock migrates in the Northern summer to the abundant feeding grounds of the polar regions the Southern stock migrates north towards the equator to calf in warmer tropical waters (Young 1999). One example of a mysticete that exhibits antitropical migratory patterns is the Right Whale, Eubalaena glacialis. The Right Whale is approximately 15 meters long and weighs up to 70 tons (Minasian et al 1984). It is located in temperate waters and in subpolar feeding waters where it consumes massive amounts copepods and euphausids.

Blue Whales, or Balaenoptera musculus, also have a wide-ranging distribution and an antitropical migratory pattern. The largest predator ever to inhabit the earth, the Blue Whale reaches lengths of 28 meters and can weigh up to 110 tons. Its size is maintained by the consumption of euphausids, crustaceans, and small schooling fish. In addition, Blue Whale calves consume milk with one of the highest known fat contents, allowing them to gain approximately 200 lbs. per day! Although the migration patterns of the Northern and Southern Hemisphere Blue Whale stocks are largely accepted as antitropical, in actuality their migratory patterns are poorly understood as Blue Whales migrate and forage in the open ocean, rarely venturing into coastal waters (Minasian et al 1984).

Perhaps the most prevalent and celebrated antitropical migrating mysticete is the Humpback Whale, Megaptera novaeangliae. The Humpback Whale is approximately 19 meters and can weigh up to 53 tons. It can be found in all ocean basins, migrating to polar latitudes in the Northern summer to feed on approximately 1.5 tons of krill, plankton and other small pelagic fish per day (Ellis 1980). Today the Humpback Whale remains under the scrutiny of the scientific community as well as the legislation of the Marine Mammal Protection Act as original stocks were significantly depleted by the overexploitation of the whaling industry.

The second type of mysticete migratory pattern and distribution, termed wide-ranging, best describes those mysticetes that are found in all ocean basins and almost all latitudes. The Fin Whale, Balaenoptera physalus, is one example of a cosmopolitan mysticete. Reaching lengths of approximately 20 meters and weights of 80 tons, the Fin Whale migrates in the northern summer to the highly productive polar waters to feed on crustaceans and small pelagic fish. Conversely, in the northern winter the Fin Whale migrates to warm equatorial waters to breed and subsequently calf (Ellis 1980 and Minasian et al 1984).

Another example is the Minke Whale, Balaenaptera acutorostrata, found in all ocean basins specifically temperate waters. Its size of approximately 9 meters and weight of up to 10 tons is obtained by the consumption of shoaling fish, krill and copepods. The Minke Whale follows a typical mysticete migratory pattern, feeding in cold polar waters in the northern summer and calving in warmer waters in the Northern winter (Minasian et al 1984).

The final example of a migrating mysticete is the Gray Whale, Eschrictius robustus. The Gray Whale is approximately 15 meters and 30 tons. E. robustus is an eclectic mysticete as it is a benthic feeder, foraging on amphipods and microorganisms in kelp fronds. The Gray Whale’s winter migration is one of the longest, as it travels from the cold feeding waters of the Chuchki Sea, down the North American Coastline and to the warm lagoonal waters of Baja, California (Darling et al 1998).

Although the list of those migrating mysticetes is seemingly long, there are only a few examples of those mysticetes that do not migrate across latitudes. The term given to those whales that are generally distributed in temperate and tropical waters is pan-tropical. One example of this type of distribution is the Bryde’s Whale, Balaenpotera edeni. The Bryde’s Whale is approximately 15 meters and 22 tons. It is found between 40°N and 40°S where it finds the warmer waters optimal for the foraging on schooling fish and the calving of their young (Minasian et al 1984).

Conversely, the Bowhead Whale, Balaena mysticetus, is categorized as having a circumpolar distribution as it does not venture out of the cold polar regions despite the seasonal occurrence of closing sea ice and the dangerous conditions of the polar waters. The Bowhead Whale obtains lengths of 15 meters and weights of 65 tons by foraging on the seasonal abundance of copepods and crustaceans of the Arctic waters (Bowhead Whales 1999).

The Sei Whale, Balaenoptera borealis, and the Pygmy Right Whale, Caperea marginata, are two mysticetes that have eluded the early whaling fleets as well as the technologically superior satellite tracking systems and contemporary scientists alike. The Sei Whale is approximately 18 meters and 24 tons. It is found in all ocean basins however its migratory pattern is extremely irregular and equally difficult to map. The Sei Whale has developed opportunistic feeding on schooling fish and euphausids therefore it will feed and most likely follow the most predominant food source in a particular region. The sei’s irregular diet may account for its appearance in an unusual region and subsequent disappearance and our utter confusion as to the migratory pattern of B. borealis (Horwood 1987).

The Pygmy Right Whale has successfully mystified the scientific community beyond even the Sei Whale. Reaching lengths of 6.5 meters, the Pygmy Right Whale is thought to be located between 30° and 50° S where it feeds on copepods. Its migratory pattern is unknown as only a few sightings and strandings have been documented. It is largely accepted however, that their migration corresponds to the abundance of a food source.

In summarizing migrations there are several accepted theories that support the migratory patterns of the aforementioned mysticetes. In most migratory observations it has been seen that most migrations are a direct result of the seasonal abundance of food in the upwelling regions of cold polar waters. Conversely, the migration of mysiticetes to warm temperate and tropical waters allows for optimal conditions for breeding and calving. In the example of the Blue Whale, migration to warmer and calmer equatorial waters provide a safe haven for newborn calves as well as to those adults who would inevitably become entrapped within closing sea ice.

In addition, long-term migrations could also be a reflection of the evolutionary history of mysticetes. Areas of high productivity have changed over time thus migrations to feeding grounds could be for survival purposes while migrations back to warmer waters could be related to the familiarity of the original region in which they evolved.

The rationale for those mysticetes that do not migrate is perhaps less clearly understood. There are many proposed ideas and theories however, it can not be assumed that there is a single reason to explain why most mysticetes migrate while the Bowhead and Bryde’s whale have evolved in some way as to avoid the long journey across the latitudes. In the example of the Bowhead Whale, perhaps there was no evolutionary need for a migration pattern as they are found in polar waters that enjoy six months of high productivity, annually. Despite the low productivity of the polar waters in the remaining six months the decreased food abundance is still great enough to sustain the Bowhead Whale populations as the migratory mysticete species have traveled to the warmer waters to breed and calf. This constant feeding could then allow for a greater amount of blubber retention and a more efficient means of thermoregulation, which are both essential components in marine mammal homeostasis.

Alternatively, the Bryde’s Whale has opted to remain in warmer waters. Perhaps they are not physiologically adapted to counteract the colder conditions but rather to avoid heat exhaustion while in the warmer waters. By feeding year round in warmer waters they are able to maintain a higher metabolism and are subsequently able to burn fat instead of storing it as blubber.

In addition to physiological adaptations, some mysticetes such as the Pygmy Right Whale and the Sei Whale have such diversity in diet that it is not necessary to migrate, as food is always readily available. Likewise, some mysticetes are observed to migrate with schooling fish, independent of any seasonal changes.

Perhaps marine mammal crusaders have successfully overlooked the most obvious theory that may explain why marine mammals have evolved differing migratory patterns - human impact. Throughout history we have mastered the art of overexploitation. We have forced numerous species into unintended niches and even into extinction. It is quite feasible to wonder that it may in fact be our excellent whaling efforts that have successfully limited the migration of different mysticetes and ultimately confined them to a route that evolution never intended. For example, the Gray Whale, originally abundant throughout the Pacific Ocean is now confined to a coastal migratory route. Coincidence alone cannot effectively explain a simultaneous decrease in the population of a species as well as its distribution.

In conclusion, it can be seen that although the scientific community holds fast to its ideas and theories on mysticete migrations not one can be proven, only supported. For now, mysticete migration patterns are infallible assumptions subject to the harsh scrutiny of the scientific community upon each surfacing observation and idea.

Bowhead Whale. Accessed October 26, 1999. Offshore/Inshore Fisheries Development. http://www.ifmt.nf.ca/mi-net/fishdeve/bowhead.htm

Darling, James et al. 1998. Gray Whale (Eschrictius robustus) habitat utilization and prey species off Vancouver, Island, B.C. Marine Mammal Science. 14: 692-718.

Ellis, R. 1980. The Book of Whales. New York: Alfred A. Knopf, Inc.. pp28-89.

Horwood, Joseph. 1987. The Sei Whale: Population Biology, Ecology andManagement. London: Croom Helm Ltd.. pp63-86.

Minasian, S. et al. 1984. The World's Whales. Washington, D.C.: Smithsonian Books. pp36-78.

Young, Robert. 1999. MSCI375 Lecture notes. Coastal Carolina University.

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