Fin Whales, Balaenoptera physalus
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Description & Behavior
Fin whales, Balaenoptera physalus (Linnaeus, 1758), like all rorquals (Family Balaenopteridae, the family that also includes blue whales, Bryde's whales, humpback whales, minke whales, and sei whales) these long, slender whales are much more streamlined than other large whales. They have a pointed snout, paired blowholes, and a broad, flat rostrum (upper part of the head). Their throat grooves, in addition to streamlining their shape, allow their throat area (called the cavum vent-rale) to expand tremendously during feeding. This allows them to consume large amounts of food-laden water which is then expelled through their baleen plates leaving the fish or krill for swallowing. This efficient system enables the largest animals on earth to feed on some of the smallest. Their baleen plates are broad and short and their dorsal fin is falcate (curved).
There are two subspecies of fin whales, Balaenoptera physalus:
1. Northern fin whales (northern hemisphere), B. physalus physalus
2. Southern fin whales (southern hemisphere), B. physalus quoyi
All members of the Order Cetacea (includes all whales; toothed and those using baleen) are believed to have evolved from terrestrial hoofed mammals like cows, camels, and sheep some 45 million years ago—that's about 40 million years before humans! Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and, strangely, have suggested that the closest land-bound living relative of whales may be the hippopotamus. Throughout their evolution, cetaceans have become perfectly suited to an aquatic environment. Cetaceans illustrate an example of adaptive radiation among mammals. Adaptive radiation allows mammals as a group to effectively inhabit the land, the sea, and the air through the development of special adaptations needed to survive in each of these environments. Members of the Order Cetacea have undergone a number of changes or adaptations needed to fare well in their watery home: their bodies have become streamlined for efficient movement through the water; their forelimbs have been modified into flippers which aid them in steering; their hind limbs have disappeared almost completely; their tail has widened and consists of two large flukes which propel them powerfully through the water by moving up and down as opposed to the side-to-side motion of fish; in place of hair they have developed a thick layer of fat called blubber under the skin that insulates them from the cold and provides buoyancy; and the position of their nostrils has shifted to the top of their head creating a blowhole that allows them to effectively come to the surface for air. A whale's blowhole generally reaches the surface before the rest of its body.
Adapting to the Sea
In addition, a number of other changes have taken place to help whales adapt to life in the sea. Many of these changes are related to the position and abilities of their sensory organs, as life in the water is not the same as life on the land. Sound and light travel differently in water than they do in the air. As a result, whales have developed unique ways of hearing and seeing. Hearing in particular is highly developed in whales, so much so that they depend on it in the same way that we depend on the combination of our eyes, ears, and nose to understand the world around us. Many of the whale's sensory and reproductive organs have been internalized to reduce drag while swimming. For example, whales do not have external ears, but rely on an internal system of air sinuses and bones to detect sounds. Changes in their reproductive and parental behaviors have also taken place, enabling whales to provide optimum care for their young in the cold, large ocean. Along with these differences, cetaceans do, however, possess many of the same physiological systems such as circulatory, digestive, respiratory, and nervous systems as the land mammals from which they evolved. For instance, many species possess multi-chambered stomachs even though there is no obvious advantage to having this characteristic, unlike cows that need stomachs with four compartments to digest their fibrous diet of plant matter.
Fin whales are the second largest animal after blue whales. Adult males measure up to 24 m in the northern hemisphere, and 26.8 m in the southern hemisphere. Females are slightly larger than males. Weight for both sexes is between 45,360-63,500 kg. Fin whales are long, sleek, and streamlined, with V-shaped heads which are flat on top. A single ridge extends from their blowhole to the tip of their rostrum (upper part of head). There is a series of 56-100 pleats or grooves on the underside of their body extending from under their lower jaw to their navels.
Fin whales are light gray to brownish-black on their back and sides. Two lighter "colored" chevrons begin midline behind their blowholes and slant down their sides towards their flukes (tails) on a diagonal upward to their dorsal fin, and sometimes recurving forward on the back. Their ventral (under) side, flippers, and flukes are white. Their lower jaw is gray or black on the left side and creamy white on the right side. This asymmetrical coloration extends to their baleen plates as well and is reversed on their tongue.
Fin whales have a prominent, falcate (curved) dorsal fin located far back on their body. Their flippers are small and tapered, and their fluke is wide, pointed at the tips, and notched in the center. Like humpbacks, fin whales also communicate through vocalizations.
World Range & Habitat
Fin whales are found in all oceans of the world. They may migrate to subtropical waters for mating and calving during the winter months and to the colder areas of the Arctic and Antarctic for feeding during the summer months, though recent evidence suggests that fin whales may disperse into deep ocean waters during winter rather than migrating between winter and summer regions.
Feeding Behavior (Ecology)
Fin whales, Balaenoptera physalus, feed mainly on small shrimp-like creatures called krill or euphausiids and schooling fish. They have been observed circling schools of fish at high speed, rolling the fish into compact balls then turning on their right side to engulf the fish. Their color pattern, including their asymmetrical jaw color, may somehow aid in the capture of such prey. They can consume up to at least 1,800 kg of food a day. As a baleen whale, fin whales have a series of 262-473 fringed overlapping plates hanging from each side of the upper jaw, where teeth might otherwise be located. These plates consist of a fingernail-like material called keratin that frays out into fine hairs on the ends inside the mouth near the tongue. The baleen on the left side of the mouth has alternating bands of creamy-yellow and blue-gray color. On the right side, the forward 1/3 section of the plates is all creamy-yellow. The plates can measure up to 76 cm in length and 30 cm in width. During feeding, large volumes of water and food can be taken into the mouth because the pleated grooves in the throat expand. As the mouth closes water is expelled through the baleen plates, which trap the food on the inside near the tongue to be swallowed.
Adult males reach sexual maturity at about 6-10 years of age. As in some other whale species, sexual maturity is reached before physical maturity. Gestation is 12 months and calves are born at 3 year intervals. Length at birth is 5.5-6.5 m and weight is 1,814 kg. Calves nurse for 6 months and are weaned when they are 10-12 m in length.
Conservation Status & Comments
Fin whales are found most often alone, but groups of 3-7 individuals are common and larger groups may occur at times. The fin whale's blow is tall and shaped like an inverted cone. Their dive sequence is 5-8 blows approximately 70 seconds apart before a long dive. Fin whales do not raise their flukes before the long dive, which can be as deep as 230 m.
Their speed and their preference for the vastness of the open sea, gave them almost complete protection from the early whalers. With modern whaling methods, however, fin whales are easy victims. As blue whales were depleted, the whaling industry turned to the smaller, still abundant fin whales. As many as 30,000 fin whales were slaughtered each year from 1935 to 1965. The International Whaling Commission (IWC) placed them under full protection in 1966 beginning with the North Pacific population. The present populations are estimated to be about 40,000 in the northern hemisphere and there may be as many as 15,000-20,000 in the southern hemisphere, this is just a small percentage of the original population levels.
Fin whales are classified as Endangered (EN A1d) on the IUCN Red List of Threatened Species:
A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered (see Section V), and it is therefore considered to be facing a very high risk of extinction in the wild.
References & Further Research
ACS fin whale Cetacean Fact Sheet - American Cetacean Society
Cetacea - Whales, dolphins, and porpoises
Jefferson, T.A., S. Leatherwood, and M.A. Webber, FAO species identification guide, Marine mammals of the world, Rome, FAO. 1993. 320 p. 587 figs.
U.S. Fish & Wildlife Service Endangered Species
Research Balaenoptera physalus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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