Gulf of Mexico Bryde's Whale

Gulf of Mexico Bryde's (pronounced "broodus") whales are members of the baleen whale family and a subspecies of the Bryde’s whale. With likely less than 100 individuals remaining, Gulf of Mexico Bryde’s whales are one of the most endangered whales in the world. Recovery of the species is dependent upon the protection of each remaining whale.

The Gulf of Mexico Bryde’s whale has been consistently located in the northeastern Gulf of Mexico, along the continental shelf break between 100 and about 400 meters depth. They are the only resident baleen whale in the Gulf of Mexico and are distinct from Bryde’s whales worldwide.

The most significant threats facing Gulf of Mexico Bryde’s whales are energy exploration and development, oil spills and spill response, vessel strikes, ocean noise, ocean debris, and entanglement in fishing gear. The Gulf of Mexico Bryde’s whale’s very small population size and limited distribution increase their vulnerability.

All Bryde’s whales are protected under the Marine Mammal Protection Act, including the Gulf of Mexico subspecies. In 2019, NOAA listed the Gulf of Mexico Bryde’s whale as endangered under the Endangered Species Act.

Gulf of Mexico Bryde’s whales are similar shape to  sei whales, but they are smaller and prefer warmer waters. Unlike other rorquals, which have a single ridge on their rostrum, Bryde’s whales have three prominent ridges in front of their blowhole. Their body is sleek, and their flippers are slender and pointed. Gulf of Mexico Bryde’s whales are uniformly dark gray on top with a pale to pink belly with some pale blotches.

Male Gulf of Mexico Bryde’s whales may be slightly smaller than females. The head of a Gulf of Mexico Bryde's whale makes up about one quarter of its entire body length. The whale has a broad fluke, or tail, and a pointed and strongly hooked dorsal fin located about two-thirds of the way back on its body.

Worldwide, Bryde’s whales have 40 to 70 throat grooves on their underside that expand while feeding and 250 to 410 short baleen plates on each side of their mouths that act as strainers as they feed. Gulf of Mexico Bryde’s whales have large, dark grey to black baleen with white bristles in their mouths; this baleen is used to filter small animals from seawater.

Gulf of Mexico Bryde’s whales are usually seen alone or in pairs, but may form larger, loose groups associated with feeding. Like Bryde’s whales worldwide, the Gulf of Mexico Bryde's whales are known to be periodically “curious” around ships and have been documented approaching them in the Gulf of Mexico. Limited data suggest that Gulf of Mexico Bryde’s whales spend the majority of their time within 50 feet of the water’s surface, similar to other Bryde’s whales in the world.

Little is known about their foraging ecology and diet. Based on behavior observed during surveys, Gulf of Mexico Bryde’s whales do not appear to forage at or near the surface but are thought to feed just at or above the seafloor, but exactly what they are feeding on is unknown. Bryde's whales in other parts of the world  feed in the water column on small crustaceans and schooling fish such as anchovy, sardine, mackerel, and herring. These prey do occur throughout the Gulf of Mexico.

As a baleen whale, Gulf of Mexico Bryde’s whales produce a variety of highly stereotyped, low-frequency tonal and broadband calls for communication purposes. In the Gulf of Mexico, Bryde’s whale call types have been reported to be composed of downsweeps and downsweep sequences.  NMFS scientists are researching what other call types the whales produce so that they can use special underwater recording instruments to learn more about when and where the whales go.

Scientists believe that the historical distribution of Gulf of Mexico Bryde’s whales may have once encompassed the north-central and southern Gulf of Mexico. The historical range in Mexican waters is not well known. For the past 25 years, Bryde’s whales in U.S. waters of the Gulf of Mexico have been consistently located in the northeastern Gulf of Mexico along the continental shelf between 100m and about 400m depth.  NMFS scientists are conducting research to better understand if the whales’ distribution is broader and how frequently they may occur in other areas.   The Gulf of Mexico Bryde’s whale is one of the few types of baleen whales that do not make long-distance migrations. They remain in the Gulf of Mexico year-round.

The Gulf of Mexico Bryde's whales are reproductively isolated and on a unique evolutionary trajectory. There is a low level of genetic divergence and they are not mixing with other Bryde’s whales.

Given information on Bryde’s whales worldwide, it is possible that Gulf of Mexico Bryde's whales reproduce every two to three years, reach sexual maturity at age 9, and mate year-round. Globally, Bryde’s whales are generally pregnant for 10 to 12 months, and calves may nurse up to 12 months.

The main threat to Gulf of Mexico Bryde’s whales are its small population size and restricted range. These whales are also exposed to a variety of other anthropogenic stressors and threats, including energy exploration and development, oil spills and spill response, vessel strikes, and ocean noise. With such a small population size, the death of a single whale due to any of these stressors could have devastating consequences for the population’s recovery. 

Vessel Strikes

Accidental vessel strikes can injure or kill Gulf of Mexico Bryde’s whales. The northern Gulf of Mexico experiences a high amount of ship traffic where several commercial shipping lanes cross through Bryde’s whale habitat. In 2009, a female Gulf of Mexico Bryde’s whale was found dead in Tampa Bay. A necropsy was performed and its death was determined to be the result of being struck by a vessel.  NMFS scientists are studying photos of living whales to evaluate their health which includes estimating how many show evidence of having survived vessel strikes.

Limited data suggest that Bryde’s whales spend the most of their time within about 50 feet of the water’s surface. The risk of vessel strikes is significant given the location of commercial shipping lanes and other transiting vessel traffic, and the whale’s swimming behavior.

Ocean Noise

A variety of human activities in the Gulf of Mexico produce a significant amount of underwater noise. Shipping traffic and energy exploration and development activities, such as seismic airgun surveys to find oil and gas fields, create low frequency noise, which overlaps with the hearing range of Bryde’s whales. It is likely that the Gulf of Mexico Bryde’s whales rely on their hearing to perform critical life functions such as communication, navigation, finding a mate, locating prey, and predator avoidance. As marine noise increases, the resulting disruption to these life functions can result in adverse physical and behavioral effects to Gulf of Mexico Bryde’s whales.

Energy Exploration and Development

The Gulf of Mexico is highly industrialized due to expansive energy exploration and production that requires drilling rigs, platforms, cables, pipelines, and ship support. Habitat in the north-central and western Gulf of Mexico, which includes the Gulf of Mexico Bryde’s whales’ historical range, has already been significantly modified by the presence of thousands of oil and gas platforms.  These activities also increase risk of vessel strike from support ships and add noise to the environment from vessel traffic and seismic surveys, as described above.

Oil Spills and Responses

Oil spills are a common occurrence in the Gulf of Mexico. Exposure to oil spills may cause severe illness or death of marine mammals. Oil can get stuck in the baleen that the Gulf of Mexico Bryde’s whales use to eat. This makes it difficult for them to feed and can cause them to swallow oil. Exposure to oil spills can also lead to lung and respiratory issues (inhalation), increased vulnerability to other diseases and infections (ingestion), and irritation of the skin or sensitive tissue in the whale’s eyes and mouths (absorption). Additionally, exposure to oil spills can even have reproductive impacts.

Chemicals used to respond to oil spills, called dispersants, may also be toxic to Bryde’s whales. Whales continue to face threats from continued exposure to oil and dispersants in the environment long after the oil spill and spill response are considered over. Additionally, their prey is often killed or contaminated by the spill.

The Deepwater Horizon oil spill showed how an oil spill can negatively affect Gulf of Mexico Bryde's whales. While the DWH platform was located outside Gulf of Mexico Bryde’s whale habitat, scientists estimate nearly half of the oil spill footprint overlapped with the whales’ habitat. As a result, it is estimated that their population decreased by 22 percent.