Members of the whale family Balaenopteridae are known as the Rorqual whales. “Rorqual” is a Norwegian term that means “furrow whale,” referring to the throat grooves found in all species in this family. These grooves extend from underneath the lower jaw back to at least the pectoral flippers and are folds of skin and blubber. When a rorqual feeds, it lunges forward at high-speed, and these grooves expand, filling the mouth with a huge amount of water and prey. When the whale closes its mouth, it uses its tongue to strain the water through the baleen plates, trapping small fish and zooplankton. In addition to throat grooves, the other characteristic common to all rorquals is a dorsal fin.
With the exception of the minke whale, all rorquals are very large, but they are also streamlined and capable of swimming at incredible speeds. Most of the whales in this group have similar body shapes and fin shapes and placements, sometimes making it difficult to distinguish one species from another. At a distance, a small blue whale looks much like a fin whale, and unless you are close enough to see the lower jaw, a small fin whale and a large sei are identical in appearance. Humpback whales with their long pectoral fins are usually easy to differentiate from other rorqual species, and minke whales are much smaller than any other species in the family Balaenopteridae. Rorquals have flattened heads and two, centrally-located blowholes. The dorsal fin is located approximately one-third of the body length forward from the fluke notch, and the tail flukes are large and wide.
In this post, I will briefly cover blue whales, fin whales, sei whales, and minke whales, and next week, my post will be about humpback whales. The reason why I’m dividing it up like this is that there is far more information about humpbacks than there is about the other species in this family. While it is known that most rorquals feed in high latitudes during the summer and breed and give birth during the winter in temperate or tropical latitudes, biologists do not know how far they migrate and what percentage of the population migrates. We see fin whales and even humpbacks all winter here on Kodiak Island, so it is clear that not all individuals migrate every year.
Blue whales are the largest animals to have ever lived on earth. Females may reach 90 ft. (28 m) in length. They are a mottled bluish gray and streamlined with a broad, rounded head, long, slim flippers, and a very small dorsal fin that is located so far back toward the flukes that it is usually only seen when they are about to begin a dive. They have broad, triangular flukes are only slightly notched, and their baleen is solid black. I have never seen a blue whale, because they are usually far off shore in deep water near the continental shelf. They are rarely seen in the bays around Kodiak Island, but in the summer, they can be found in the Gulf of Alaska and the Bering Sea. I think it is interesting that the largest animal on the planet dines on one of the smallest animals. Blue whales primarily eat euphausiids, small shrimp-like organisms that are commonly called krill.
Fin whales are the second-largest species of whale. An average adult female fin whale is 73 ft. (22 m) in length, while an average male is 70 ft. (21 m). A fin whale’s upper jaw is V-shaped and flat on the top, and it has a distinct ridge on its back that extends from the dorsal fin to the tail fluke. Its dorsal fin is up to two feet tall and is curved with a steep backward angle and a blunt tip. The flukes are broad and triangular with pointed tips and a central notch. A fin whale has a light gray to brownish-black back and sides, with two lighter-colored chevrons that begin behind the blowholes and slant down the sides toward the fluke and then swirl up and end behind the eye. The undersides of the body, flippers, and fluke are white. The left lower jaw of a fin whale is dark gray, but the right lower jaw is white, and this asymmetrical coloration extends to the baleen plates. Scientists think this asymmetrical jaw color may somehow aid fin whales in capturing prey. If seen up close, the right lower jaw of a fin whale clearly distinguishes it from a blue or sei whale. Fin and blue whales produce the loudest biological sounds in the ocean, and recent research on fin whales shows that only males produce these vocalizations. The sounds are simple and consist of low-frequency moans and grunts and high-frequency pulses. Scientists suspect that males emit these sounds to attract females from great distances, and they worry that sounds from commercial ships, military sonar, seismic surveys, and ocean acoustic research may reduce the distance over which receptive females can hear the vocalizations of males.
Of all the large whales, perhaps the least is known about sei (pronounced say) whales. In the southern part of their range sei whales coexist with Bryde’s whales, and until the early 1900s, they were considered the same species. The name “sei” comes from the Norwegian word “seje”, which means pollock, because sei whales appeared off the coast of Norway each year at the same time large schools of pollock arrived to feed on the abundant plankton. Sei whales are sleek and streamlined, and are one of the fastest swimming baleen whales, reaching speeds of 22 mph. They may reach a length of 65 ft. (20 m), but a length of 54 to 55 ft. (3.7 to 16.8 m) and a weight of 14 to 17 tons is more typical. Sei whales have a dark bluish-gray body with white on the ventral surface. The flukes and flippers are dark on both the dorsal and ventral surfaces. The snout is pointed, and there is a single prominent rostral ridge running from the blowholes to the snout. The dorsal fin is tall and curved, and the baleen is uniformly ashy black with fine, silky fringes. Sei whales normally feed near the surface, and they are primarily skimmers instead of gulpers like blue and fin whales. Small copepods are their preferred food, although they will also eat other zooplankton and small fish.
Minke whales are the smallest of the rorquals. Males average 26 ft. (8 m), and females average 27 ft.(8.2 m). Both males and females weigh approximately 10 tons. The story is that the minke (pronounced mink-ey) whale was named after a Norwegian whale spotter named Meincke, who mistakenly identified a small minke whale as a blue whale, the largest of all whales. Minke whales have a very narrow, pointed jaw, a single ridge that runs from the tip of the jaw to the blowhole, and a dorsal fin that is tall and curved. The flippers are slender and pointed at the tips, and the flukes are broad, pointed, and notched in the center. The body is dark gray on the back and white on the ventral surface. There is a distinctive white band on each flipper, and the extent and orientation of the band varies between individuals. The baleen is yellowish-white. Minke whales have an inconspicuous blow that is often hard to spot in the ocean, but they do occasionally breach, and you can see the white fin band on the fin of the breaching minke in the above photo.
My post next week will be about the most famous member of the rorqual family, the humpback whale. Please let me know if you have any questions or would like to add anything to these posts.
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