Bryde's whales are small members of family Balaenopteridae, which are commonly known as rorquals. Males of this species range from 12 to 13 m long, while females are slightly larger, ranging from 13 to 14 m. Both sexes weigh 13,600 to 15,000 kg. Their body is a dark smokey grey above, and whitish below. Whales that migrate often have circular scars from lampreys and cookiecutter sharks. Their head makes up 25% of their body and has 3 ridges on the top that run from the tip of their snout to the front of their blowhole. Underneath, they have 54 to 56 throat grooves between each flipper and extend past their navel. Inside their mouth, there are 285 to 350 slate gray coarse baleen plates on each side; the longest plate is 40 cm. Bryde's whales have 54 to 55 vertebrae, along with 13 to 14 broad, thin ribs. Their dorsal fin is slightly curved or hooked, while the other fins are short, narrow, and pointed. Their tail is wide and takes up 24% of their body length. There used to be a pygmy version of Bryde's whales, but since 2003 they have been considered their own species, Omura's whales. Physically, juveniles look very similar. (Allen, et al., 2011; Jefferson, et al., 2008; Shirihai, 2006)
Bryde’s whales (Balaenoptera edeni) can be found in the Pacific, Indian and Atlantic oceans, but they mostly stay in tropical and sub-tropical waters. Due to their preference for warm water, they usually migrate towards the equator in the winter. Some small populations are mostly inactive, including a small population of about 12 whales along the coast of California. There is evidence that suggests the smaller whales found near the coasts may actually be a different species than the larger whales that live in deeper waters. ("Bryde's Whale", 2012; Allen, et al., 2011; Jefferson, et al., 2008; Shirihai, 2006)
Bryde's whales live in warm ocean waters, with temperatures ranging from 15 to 20 degrees C. They can live near the coasts or further out to sea. While pursuing prey, they may dive as deep as 300 m. (Allen, et al., 2011; Jefferson, et al., 2008; Shirihai, 2006)
There is very little information available about the mating systems of Bryde's whales, although they probably have a similar system to other related cetaceans.
Bryde's whales can begin breeding when they are 10 to 12 m long and 10 to 13 years old. Whales found near coastlines can breed throughout the year, while the whales found further out to sea breed more often in the fall months. Their gestation lasts 11 to 12 months. During the first 4 months of pregnancy, the fetus develops slowly, and develops quickly in the remaining time. At birth, calves are usually 3.4 meters long and weigh about 900 kg. Females only have one calf per breeding season. Females have a 6-month recovery period after the calf reaches maturity at 6 months of age; this is why births occur every other year. (Allen, et al., 2011; Jefferson, et al., 2008; Kerosky, et al., 2012; Shirihai, 2006; Tershy, 1992; Wiseman, et al., 2011)
Females nurse their calves for 6 months, without any help from the males. After being weaned, the calves fend for themselves. (Allen, et al., 2011; Jefferson, et al., 2008; Shirihai, 2006; Tershy, 1992)
In the wild, Bryde's whales can live 50 to 70 years, the oldest recorded individual was 72 years old; nothing is known about their lifespan in captivity. (Allen, et al., 2011)
Bryde's whales are mostly solitary. Those living near the shore may have feeding groups of 15 or less, while those living off-shore may have groups of up to 30. When they travel, about 93% of them are solitary, which is a much greater percentage than the closely-related sei whales. However, Bryde's whales feed with their own species and many other whale species without becoming aggressive. These whales do not often shoot water from their blow hole, but when they do, it rises 3 to 4 m. Their dives usually last 5 to 15 minutes, with a maximum of 20 minutes. They usually swim 1.6 to 6.4 km/h, but they can reach speeds of 19 to 24 km/h. ("Bryde's Whale", 2012; Allen, et al., 2011; Jefferson, et al., 2008; Kerosky, et al., 2012; Shirihai, 2006; Tershy, 1992; Wiseman, et al., 2011)
Movements within their primary, or home range, depend on the presence of food rather than breeding. Bryde's whales do not defend a territory. (Kerosky, et al., 2012; Oleson, et al., 2003; Tershy, 1992; Wiseman, et al., 2011)
Bryde's whales make short, but loud, low-frequency moans. Most of the sounds they make include two types of calls emitted at the same time. They can repeat these calls every 1 to 3 minutes, and many are produced while the whales are moving. Whales call back and forth, and the type of calls changes due to the size of the group. Although they likely have no sense of smell, their vision and hearing appear to be similar to that of other whales. (Allen, et al., 2011; Heimlich, et al., 2005; Jefferson, et al., 2008; Yamato, et al., 2012)
Bryde's whales are unlike other whales because they have a generalist diet, which allows them to stay in warm waters year-round where they can always find food. As baleen filter-feeders, they use multiple strategies for feeding, including making bubble nets, skimming the surface and lunging for prey. Although there is no evidence of communication while feeding, multiple whales are usually found in the same feeding location. Bryde's whales have also been seen cleaning up after other predators by eating the leftovers. The inshore groups prefer fish, specifically anchovies, sardines, mackerels, and herring, while the offshore groups eat copepods and krill. They also eat cuttlefish, squid, and octopi. Each whale generally eats about 660 kg a day, which is about 4% of their body weight. (Alves, et al., 2010; Murase, et al., 2007; Tershy, 1992)
Bryde's whales may be preyed on by killer whales and shark species. When they are approached or pursued by a predator, they try to quickly swim away. (Allen, et al., 2011; Ford and Reeves, 2008; Jefferson, et al., 2008; Shirihai, 2006)
Due to the impacts of intense whaling, we do not know the true ecological impact of these large whales. Bryde's whales host several parasites including parasitic worms, commonly called helminths. Other species found on these large whales are sea lice, copepods, amphipods, barnacles, and sea lampreys. Unlike the other species, sea lampreys can cause death, due to organ failure caused by infections or blood loss. (Magalhães Pinto, et al., 2004; Priddle and Wheeler, 1998; Ólafsdóttir and Shinn, 2013)
There are no known adverse effects of Bryde's whales on humans.
Although whaling is illegal in many parts of the world, there are still countries that do not have any laws about this practice. The International Whaling Commission was started in 1986 to help stop the hunting and killing of whales for their meat, oil, and bones. Common minke whales are the most frequently hunted species, but Bryde's whales look very similar and often are caught. In the western North Pacific, it is estimated that from 1911 to 1987, 20,000 whales were caught each year, while in South Africa an estimated 2,000 whales were caught from 1911 to 1967. (Reilly, et al., 2013)
According to CITES, Bryde's whales are classified as Appendix I, the most endangered species, but they may be changed to Appendix II, animals that are not threatened now but may become so if they are not watched closely. Bryde's whales are protected under the Marine Mammal Protection Act (MMPA), which prevents their removal from U.S. waters. Threats to this species include whaling (legal and illegal), run-ins with ships, and the possible effects of human-caused noises (including sonar), which have caused the beachings and deaths of whales and other cetaceans. Whaling harvests are sometimes hard to calculate because Bryde's whales are often grouped with other similar-looking species. Despite international laws, this species may still be at risk from illegal over-hunting. ("Bryde's Whale", 2012; Reilly, et al., 2013)
Jessica O'Grady (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
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