Sei Whale
(Balaenoptera borealis)

Federally Endangered

Description

The sei whale (pronounced "say") is smaller than the finback whale and larger than the minke whale. Sei whales are 25-50 feet in length and weigh 40 tons. Females are slightly larger than males. Sei whales can be identified by an inverted V shaped spout, which extends 6-8 feet high. The sei whale resembles the finback, and can be very difficult for the amateur to distinguish. Sei whales have smaller, more erect dorsal fins, dark undersides of the flippers and tail flukes, and bluish-gray coloration with whitish spots. Sei whales lack the asymmetric lower lip coloration and dorsal chevrons (V-shaped stripes on the upper back) of the finback. The sei whale has 30-60 pleated grooves that extend from the chin along the belly. These pleats enable the throat to expand when feeding, to accommodate a large volume of water and food. Baleen plates are rooted in the gums of the upper jaw and number between 219 to 402 plates on each side of the jaw. Map of range and known locations of sei whale

Range and Habitat

Sei whales are found throughout the world's oceans. They occur in the North Atlantic from Iceland to the Venezuela coast. They are seen infrequently in U.S. waters and very rarely in the Gulf of Maine. These whales breed and feed in open oceans. They are more frequently observed in temperate waters in the summer and subtropical waters during the winter. Two populations have been tentatively identified in the western North Atlantic. One population occurs in the Labrador Sea in June and migrates later in the summer northward along the coasts of Labrador, West Greenland, and possibly Iceland. The other population occurs off the continental slope of the United States during winter and migrates northward by mid to late June to Georges Bank, Northeast Channel, and Browns Bank. Periodic movements into the Gulf of Maine occur rarely, and may be followed by years or decades with no sightings.

Life History and Ecology

Sei whales are usually seen as singles or pairs, but sometimes thousands may gather if food is abundant. Like northern right whales, they are "skimmers," meaning they feed near the water surface using their baleen to filter small shrimp-like animals (copepods, euphausiids, amphipods) and schooling fishes from the water column. They are fast and swim at speeds of up to 35 miles per hour. Whalers identify sei whales by their swimming behavior, which includes erratic changes in direction. They are shallow divers and only remain submerged for 5-10 minutes.

Breeding occurs between November and March, with the peak in January. The gestation period lasts 10½ to 12 months. Calves are dependent on milk from the mother for about nine months and are weaned when they reach 24-27 feet in length. Both sexes become sexually mature at about 8-10 years of age, which corresponds to a length of about 36 feet for males and 40 feet for females. They do not reach full adult size until they are about 25 years old. Breeding occurs at intervals of three years. They may live as long as 74 years.

Threats

Commercial whaling depleted populations in all oceans. Like other large whales, sei whales are at risk of collisions with ships. Marine ecosystem changes induced by global warming and pollution may affect food availability. Recreational whale watching may occasionally cause harassment, but this is believed to be insignificant. Mortality rates from these causes are not limiting population recovery at this time.

Conservation and Management

Hunting of sei whales began in the North Atlantic in the 1800s. A whaling station at Blandford, Nova Scotia killed hundreds of sei whales in the 1900s. In 1972, populations were estimated to be only 21 percent of original numbers. In the early 1980s, there were estimated to be as few as 2,200-2,300 individuals in U.S. Atlantic waters. Hunting is no longer a problem for sei whales as a result of protection received through the International Whaling Commission, Endangered Species Act, and Marine Mammal Protection Act. Cetacean experts believe sei whale populations to be increasing, but data are sparse. Given the species' pelagic (open-ocean) ecology, there have been no reported fishery-related mortality or injuries. The Maine Department of Marine Resources has lead management authority for marine mammals, including the sei whale.

Recommendations:

The Maine Department of Marine Resources recommends that National Marine Fisheries Service Guidelines for whale protection be employed. Regulations can be found at www.nero.nmfs.gov /whaletrp/. Current (2002) guidelines include the following:

Dedicate state education and outreach efforts to fishermen.
Close critical whale habitats to some types of fishing gear during times when whales are likely to be present.
Prohibit some fishing practices (e.g., leaving inactive gear for more than 30 days) that increase risk of entanglement.
Require some gear modifications in federal waters (e.g., knotless weak links in buoy lines for lobster traps and gillnets, no floating line at the surface) to reduce risk of entanglement.
Utilize state and federal contacts for Whale Disentanglement Networks to locate entangled whales and remove gear. If you see an entangled whale, call the Northeast Disentanglement Network at 1-800-900-3622, the Coast Guard Station nearest you on 16 VHF Radio, the Maine Whale Take Reduction Coordinator, or the Maine Marine Patrol.
Investigate and implement measures to reduce ship strikes of whales, including: 1) routing ships around observed whales, 2) restricting speed of vessels operating in whale habitats, 3) requiring mandatory shipping lanes when transiting through critical habitat areas, and 4) providing ship captains operating in critical habitats with the latest whale sighting data.
Whale watchers must employ the following guidelines: 1) No vessel should approach closer than 300 yards. When whales are nearby, move at a constant, slow, "no wake" speed. 2) Do not engage props while whales are within 100 yards and do not chase whales. 3) When watching whales, do not box them in or cut off their path to prevent them from leaving. 4) Do not attempt to approach mothers with young calves. 5) Do not operate aircraft within 300 yards of a whale.
Plan for protection of critical whale habitats in state and federal oil spill contingency planning.

For more information contact Maine's Endangered Species Program at (207) 941-4466.

DEPARTMENT INFORMATION

Sei Whale (Balaenoptera borealis)