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 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 responses, vessel strikes, ocean noise, and entanglement in fishing gear. The Gulf of Mexico Bryde’s whale’s 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 look similar 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 are usually 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 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 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 whale is known to be periodically “curious” around ships and has been documented approaching them in the Gulf of Mexico. Limited data suggests that Gulf of Mexico Bryde’s whales spend the majority of their time within 50 feet of the water’s surface.

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. In general, Bryde's whales feed in the water column on small crustaceans and schooling fish such as anchovy, sardine, mackerel, and herring. These prey 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.

Scientists believe that the historical distribution of Gulf of Mexico Bryde’s whales 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 break between 100m and 400m depth. This area has been identified as the Bryde’s whale Biologically Important Area (LaBrecque et al., 2015) . The Gulf of Mexico Bryde’s whale is one of the few types of baleen whales that do not migrate. 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 likely that Gulf of Mexico Bryde's whales reproduce every two to three years, reach sexual maturity at age 9, and mate year-round. Bryde’s whales are generally pregnant for 10 to 12 months, and calves may nurse up to 12 months.

Gulf of Mexico Bryde’s whales are exposed to a variety of stressors and threats, including energy exploration and development, oil spills and spill response, vessel strikes, and ocean noise. The species small population size and restricted range increases their vulnerability to existing threats.

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.

Limited data suggests 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, the whale’s swimming behavior, and the low ability of ships to change course quickly to avoid a whale.

Ocean Noise

A variety of manmade sources in the Gulf of Mexico produce a significant amount of underwater noise. Shipping and energy exploration and development activities 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, mate finding, food location, and predator avoidance. As marine noise increase, the resulting interruption 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. Vessel traffic and noise associated with these activities can modify or destroy Gulf of Mexico Bryde’s whale habitat. 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.

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, increased vulnerability to other diseases and infections, and irritation of the skin or sensitive tissue in the whale’s eyes and mouths. Additionally, 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 is considered over. Additionally, their prey is often killed or contaminated by the spill.

The Deepwater Horizon oil spill showed how an oil spill can 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, their population decreased by an estimated 22 percent.