Sei Whale

Balaenoptera borealis

Photo courtesy of  Christin Khan from NOAA

Introduction to Sei Whale

One of the Baleen Whale species is the Sei Whale. It is ranked #3 in terms of overall Baleen Whale size. This is believed to be one of the fastest of all whales, and it can easily travel several miles per day while migrating. They are often mistaken for Bryde’s Whales and Fin Whales due to the similarities in size and coloring.

Sei Whale Description

The Sei Whale has a body that is very slender. They feature a pointed snout and very short pectoral fins. They have a wide and tall dorsal fin. When fully grown, they can be from 40 to 60 feet long. They can weigh up to 100,000 pounds. Females are slightly larger than the males. They are dark gray in color with various white markings on the body. There are 300 to 380 baleen plates on each side of the mouth. They have two blowholes.

Sei Whale Distribution

You will find the Sei Whale living in most of the oceans as well as the seas that are adjoined to them. They aren’t often seen though as they tend to stay in the deeper waters offshore. They like the middle range temperatures as they avoid polar and tropical regions. They also avoid bodies of water that are semi-enclosed. Annually, they will migrate, so that they can spend summers in cooler water and winters in the subtropical waters.

Sei Whale Behavior

They don’t dive very deep, and can remain under the water for up to 10 minutes. However, they usually surface around 5 minutes for air. There isn’t much information known about their social behaviors. They are often seen in very small groups ranging from 2 to 5 members. At times, they will be seen in very large numbers if there is an abundance of food in any given location. They do use vocalizations to communicate , but they do so at a low frequency.

Sei Whale Feeding

In order to get their prey, the Sei Whale will swim rapidly through the prey. They will twist their body from side to side, skimming to help them with filtering the food supply into the baleens. There will be a considerable amount of water that is taken in at the same time. They don’t rely on echolocation to find food, but they do offer sonic bursts with pulses.

The majority of the feeding occurs in the early morning around dawn. They will engage in a variety of behaviors in to get their food supplies. They consume plankton, schools of fish, and squid. They take part in skimming as well as gulping activities to get plenty of food. They may consume seabirds at times too that are in the same area looking for their own food resources.

Sei Whale Reproduction

They can start mating when they are about 10 years of age. However, they will still continue to grow until they are about 25 years old. It is believed that overall size plays more of a role in their mating time than their age. When they are about 45 feet long they are more likely to take part in mating.

There isn’t much data regarding the mating of the Sei Whale. It is believed that this is a time though when they will become more social. Mating will occur in the winter time for those that live in the Northern Hemisphere. It will occur in the summer months for those that live in the Southern Hemisphere. It takes from 10 to 12 months for the calf to be born after mating. The young can be up to 15 feet long and weigh up to 1,500 pounds at birth.

The young will form a tight bond with the mother. For the first 7 months they will consume milk from her body. The females usually give birth every other year. However, if her offspring is killed then the female will often mate again the following year. It is believed that this species of whale has a lifespan that ranges from 50 to 70 years.

Sei Whale Conservation Status and Threats

Whaling has played a huge role in the depletion of the population for the Sei Whale. By the time they were protected from commercial whaling in the 1980s, it is believed over half of their population was diminished. It is believed many of them were killed due to being mistaken for other whale species including the Blue Whale and the Fin Whale. In 1976, they were protected and by 1986 moratorium.

In 2001, Iceland stated that it may allow commercial whaling of the Sei Whale, the Minke Whale, and the Fin Whale. There are several other countries too that seem to be in favor of lifting the ban.

There is insufficient data to determine how many of them are in the wild today. Conservation efforts focus on trying to eliminate illegal hunting, reducing pollution in the water, and reducing collisions with vessels.

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