From 100 feet long to 10 feet long: a huge difference in size. These two whale species share many cetacean characteristics, but in some ways are very different.
Believed to be the largest mammals on Earth, past or present, the blue whale (Balaenoptera musculus) weighs in at around 150 tons and is roughly 100 feet long. It cannot compete with the smaller sperm whale for brain size, however, as this species reportedly has the largest brain of all mammals. The blue whale is also huge on sound. Having one of the loudest calls in nature, a blue whale’s song can travel several miles. It has been measured at between 155 and 188 decibels at source. Researchers have observed each note of the song to last between 10 -30 seconds, and songs to comprise 4 notes, lasting 2 minutes.
Sadly, the number of blue whales in existence is not on a scale with their size. Estimates put the blue whale population at between 200,000 and 300,000 before whaling increased to an industrial scale. Even though this level of whaling has ceased, the number of blue whales is now at around 5,000 – 12,000. Although it is the largest mammal, the blue whale feeds on some of the smallest creatures, such as the shrimp-like krill. As a baleen whale, and therefore not toothed, it filter-feeds using its baleen plates. It has a small oesophagus relative to its size, so food has to be small enough to be swallowed without being broken down by chewing.
Blue whales have regular migratory patterns, travelling thousands of miles between cold polar waters where they feed intensively, and warmer tropical waters for mating and birthing.
Pygmy sperm whale
In general, toothed whales are much smaller than any baleen whales. The exception is the sperm whale, which can grow up to about 70 feet long. At around 10 feet in length, the (toothed) adult pygmy sperm whale (Kogia breviceps) is significantly smaller.
The pygmy sperm whale uses echolocation (a sound emitted to locate prey, similar to radar) to help in locating prey. It has between 20 and 32 teeth, most usually set in the lower jaw, although some have been found to have up to 3 pairs of teeth in the upper jaw as well.
Its diet consists of squid, octopus and shrimp; being toothed, it can eat far larger prey than the filter-feeding blue whale!
Although small, it does have one advantage over predators that larger whales do not. As a defence mechanism, it can release a burst of reddish-brown fluid from its intestines, which allow it cover to dive and escape.
It is not known how many pygmy sperm whales there are, as they are not often seen. Most of what is known about them has been through strandings. Preferring warmer and deeper waters, they have been sighted in different sub-tropical and tropical waters. They are not known to migrate. Unlike the blue whale, they were not victim to commercial hunting, but could still be endangered as they are vulnerable to environmental change and pollution, and their echolocation can be compromised by sea traffic and ships’ sonar.