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Sei Whale




Sei Whale (Pacific)

Balaenoptera borealis

At a glance

Sei WhaleOnce one of the more abundant species of whales in the Pacific Ocean off the British Columbia coast, sei whale numbers declined dramatically due to hunting. In the 1960s, more than half of all whales caught in British Columbia waters were seis. Today, there appear to be few if any of the whales remaining in British Columbia waters, and the total population of sei whales in the North Pacific is thought to number only approximately 14,000—that’s 20 percent of its pre-whaling population. Although sei whales are now protected, scientists are not sure why the population is showing no signs of recovery.

Photo credit: NOAA

About the sei whale

A slim, streamlined whale, seis rarely approach the coast, preferring to breed and feed in the open ocean. The whales are usually found alone or in groups of two to five, and little is known about their migrations, which are likely fairly irregular. The whales become sexually mature at six to eight years of age. Calves are usually born in the winter and nurse for between four and six months.

What they eat

Sei whales feed primarily on plankton, but will also eat small fish and squid. Regardless of food species, however, sei whales seem to prefer prey that congregates in dense groups close to the surface. As with other baleen whales, such as the humpback, the sei has no teeth; instead it has a series of fringed plates—called baleen plates—hanging from each side of its upper jaw. During feeding, a sei swims near the surface with its mouth open. When the whale closes its mouth, the water is forced out and the baleen plates act as filters, trapping food on the inside ready to be swallowed.

How to recognize a sei whale

The third largest baleen whale, seis can weigh up to 40 tons and grow to between 18 and 21 metres in length; females are generally half a metre longer than males. The whale has dark grey skin with variable white undersides and light-coloured patches over its upper body. The dorsal fin is curved and the undersides of flippers and tail flukes are dark grey or bluish in colour. The sei whale can be identified easily by its inverted v-shaped spout, which reaches six to eight feet into the air.

Where the sei whale lives

Sei whales are a cosmopolitan species with a patchy oceanic distribution. The whales seem to favour deep offshore habitat and do not usually enter icy waters. Little is known about the whales’ wintering grounds.

Why it’s at risk

Decimated by whaling in the late 1800s and early 1900s, sei whale populations have shown no signs of recovery since being protected by the International Whaling Commission. Little is known about the reasons for the lack of population recovery, however many sei whales suffer from flatworms, which may cause kidney and liver problems.

What’s being done

The Pacific population of sei whales is listed as endangered and protected under the Species at Risk Act (SARA). Internationally, the International Whaling Commission (IWC) regulates hunting of sei whales.

Over the long term, recovery planning may result in management measures such as modifying guidelines for oil and gas development and seismic exploration; modifying shipping routes; establishing strict guidelines for those wishing to research the sei whale or its critical habitat; and conducting more research on potential threats.

Recovery Strategy for large whales (blue, fin and sei) has been finalized. Currently an action plan is being developed for large whales (blue, fin, sei and North Pacific right whale).

What can you do?

Sei whales will get the protection they need only if all Canadians work together to reduce threats. Find out more about sei whales and be aware of man-made threats. Do your best to reduce these threats wherever possible to better protect the whale’s critical habitat. Get involved with the Habitat Stewardship Program for Species at Risk (HSP) or another conservation organization.

Species at Risk Public Registry Profile

Source: Fisheries and Oceans Canada