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BRYDE'S WHALE
Balaenoptera brydei Anderson 1879

Order Cetacea : Family Balaenopteridae

DESCRIPTION. Bryde's whale is the second smallest of the rorquals, averaging only 12.2–13.1 m in length and 12 metric tons in weight. As with all rorquals, females tend to be a little larger than males. Maximum length is about 15.5 m. Bryde's whales are unique in having three head ridges extending from the blowholes to the end of the rostrum. This is the only baleen whale with this feature, although several have one such ridge, so the presence of three head ridges will always distinguish B. brydei. Coloration is a dark bluish gray overall but somewhat lighter in the throat area. The dorsal fin is only about 46 cm in height and rises abruptly from the back. Bryde's whales have ventral pleats extending to, or slightly beyond, the navel.

Balaenoptera brydei

DISTRIBUTION. Bryde's whales appear to be limited to tropical and warm temperate waters of the Atlantic, Indian, and Pacific Oceans and are not found in colder, high-latitude waters. There are at least a dozen verified stranding reports in the Gulf, all of them between Louisiana and southern Florida. Likewise, there are numerous live sightings in relatively shallow waters near the 100 m isobaths during every season but fall; most of the sightings have been in the De Soto Canyon region and off western Florida. Bryde's whales have yet to strand on the Texas coast, although there is a stranding record on nearby beaches in Louisiana. It is probable that one of these whales will one day strand along the Texas coast.

SUBSPECIES. The taxonomic status of B. brydei is unresolved, but at this time the species is regarded as monotypic.

HABITS. There is an unfortunate paucity of natural history and population data from the Bryde's whale, making this one of the least known of the great whales. This is primarily because, even in the 1970s, scientists did not distinguish between Bryde's and sei whales.

Bryde's whales appear to be nearshore, year-round residents of tropical and subtropical waters. Although most commonly seen in groups of 5–6, large groups of 30–40 have been observed in areas of food concentrations. This whale frequently feeds on pelagic fishes such as pilchard, mackerel, herring, mullet, and anchovies; however, cephalopods and pelagic crustaceans (krill) are also eaten.

Bryde's whales are believed to breed year-round, and their gestation period is estimated to be 12 months. Calves are about 4 m long at birth and weigh 1 metric ton. Sexual maturity is reached at 8–10 years, when the animals are about 12 m long.

POPULATION STATUS. Uncommon; strandings and observations. Bryde's whale is the most frequently stranded and observed baleen whale in the Gulf of Mexico. These whales have stranded on Gulf beaches in winter, spring, and summer, indicating they are year-round residents of these waters. Estimated abundance in the northern Gulf of Mexico is presently about 50 whales, but that number could change with further studies.

CONSERVATION STATUS. The USFWS and TPWD do not list Bryde's whale as either endangered or threatened. The IUCN listing is "data deficient; population trend unknown." Previous editions of The Mammals of Texas used the scientific name Balaenoptera edeni for this species.

REMARKS. A recent study of these whales in the Gulf of Mexico by Patricia Rosel and Lynsey Wilcox of the National Marine Fisheries Service (NMFS) evaluated genetic diversity and phylogenetic distinctiveness of the Gulf population to determine how unique it is compared with other stocks worldwide. Their study found that the Gulf population has little genetic diversity, suggesting a small population size and a history of isolation, and that the population is evolutionarily distinct from all other Bryde's whales examined to date. The scientists concluded that the level of divergence suggested a unique evolutionary lineage for the Gulf population that is equivalent to currently recognized subspecies and species within the Bryde's complex and among species and subspecies of certain other baleen whales. To quote the two scientists, "the level of divergence suggests a unique evolutionary trajectory worthy of their own taxonomic standing" and "the small population size and markedly low genetic diversity raise conservation concern for this unique group of whales." On the basis of this evidence, the National Resources Defense Council has petitioned the Secretary of Commerce, through the NMFS, to list the Gulf of Mexico population of Bryde's whale as an endangered species and designate critical habitat to ensure its recovery as required by the Endangered Species Act. The listing of this species as endangered would have major consequences for the oil and gas industry currently operating in the northern Gulf of Mexico.

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From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016.  Courtesy of the University of Texas Press.

Natural Science Research Laboratory