Sei Whales (Balaenoptera borealis)

Sei Whales on the Ledge: Throughout their distribution range, Sei whales (pronounced "say") are known for suddenly showing up in areas in some numbers to feed, taking advantage of a localized prey patch. This happened in 1986, when sei whales were commonly seen on the Ledge during July and August. They have been seen in many other years as well, but never as many as 1986, nor have any stayed for more than a few days. They are commonly seen summering on the Nova Scotian shelf. Size: Up to 65 feet, usually 45-50 feet Weight: approximately 40-50 tons as full grown adults Distinctive Characteristics: A very sleek whale with a tall dorsal fin that is curved and pointed on top. Their baleen has an unusually fine inner fringe. Unlike many other whales which will blow several times in rapid succession and then dive for a longer period, sei whales often will stay at the surface and blow once every 90-120 seconds. Diet: Sei whales have been known to eat a wide variety of prey, including many fish species and squid. However, their primary diet seems to be plankton, especially copepods. As such, they are often found in the same area as other copepod feeding whales, including right whales. Unlike other rorqual whales (those with pleats and a dorsal fin), sei whales will sometimes feed by skimming along, mouths opened, as they feed on plankton. Distribution: Sei whales are widely distributed, from the tropics up to the ice pack. However, they are somewhat more common in colder waters. Their annual movements are poorly known and understood. In many parts of their range, they are known for episodic influxes into areas where they were previously rare, but where plankton is abundant. Life History: Sei whales are born at approximately 15 feet, and 1,500 pounds. It is presumed that they are born in warm waters, although specific breeding grounds remain unknown. It is thought that females give birth once every 2-3 years, after a gestation of about a year, and the calve stay with the mother for 6-10 months. Social Organization: Sei whales are usually seen in small groups, from single animals to groups of four. However, in areas of dense prey, they may aggregate with many such groups in a very limited area. It is thought that they, like most whales, do not form long term a bond between males and females, but little is known of their breeding behavior. Population Status: Over 200,000 sei whales were killed in the 20th century, primarily in the southern hemisphere. While they are classified as endangered today, exact numbers or population estimates are difficult to generate. In general, they are thought to be fairly abundant throughout the northern hemisphere, and depleted in the southern hemisphere. The only sei whales being killed today are those killed by Japan, who started a small hunt as part of their "research" program in the North Pacific Ocean in 2002. Other Sites: Link #1    Link #2    Link #3