Rice's whales are members of the baleen whale family Balaenopteridae. With likely fewer than 100 individuals remaining, Rice's whales are one of the most endangered whales in the world. Recovery of the species depends upon the protection of each remaining whale.
The Rice'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 most closely related to Bryde’s (pronounced “broodus”) whales. In 2021, scientists determined that the Rice’s whale was a unique species, genetically and morphologically distinct from Bryde’s whales.
In 2019, NOAA Fisheries listed the Gulf of Mexico Bryde’s whale as an endangered subspecies under the Endangered Species Act. In 2021, NOAA Fisheries revised the common and scientific name of the listed entity to Rice’s whale, Balaenoptera ricei, and classification to species to reflect the new scientifically accepted taxonomy and nomenclature of the species. Like all marine mammals, the Rice’s whale is also protected under the Marine Mammal Protection Act, and given its ESA listing, it is considered depleted under the Marine Mammal Protection Act.
When the comprehensive ESA status review was completed in 2016, the team of scientists conducting the ESA status review concluded that there were likely fewer than 100 individual Rice's whales throughout the Gulf, with 50 or fewer being mature individuals. NOAA Fisheries’ most recent abundance estimate from 2017–2018 surveys in the northeastern Gulf of Mexico is approximately 50 individual Rice's whales.
Rice's whales, like Bryde’s whales, are smaller than sei whales. Unlike other rorquals, which have a single ridge on their rostrum, Bryde’s and Rice’s whales have three prominent ridges in front of their blowhole, though this feature can be difficult to observe at sea. Their body is sleek, and their pectoral fins are slender and pointed. Rice's whales are uniformly dark gray on top with a pale to pink belly. The head of a Rice'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.
Like other baleen whales, Rice’s whales and Bryde’s whales engulf large amounts of water and strain it through baleen plates that hang inside their mouths to catch their prey. They have throat grooves that expand while feeding to increase the amount of seawater, and therefore prey, that they can engulf.
Rice's whales are usually seen alone or in pairs, but may form larger, loose groups associated with feeding. Limited data suggest that Rice's whales spend the daytime diving near the seafloor bottom and spend the majority of their time at night within 50 feet of the water’s surface, similar to some Bryde’s whales.
Little is known about their foraging ecology and diet. However, data from a two Rice’s whales suggest they may mostly forage at or near the seafloor. This is in contrast to Bryde's whales that have been observed feeding in the water column and near the surface on small crustaceans and schooling fish such as anchovy, sardine, mackerel, and herring.
Baleen whales typically produce a variety of highly stereotyped, low-frequency tonal and broadband calls for communication purposes. NOAA Fisheries scientists are researching what call types the whales produce so that they can use special underwater sound recording instruments to learn more about where these whales go and when..
The historical distribution of Rice's whales may have once encompassed the northern and southern Gulf of Mexico. For the past 25 years, Rice’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 roughly 100 and 400 meters depth. A single Rice’s whale was observed in the western Gulf of Mexico off the coast of Texas, suggesting that their distribution may occasionally include waters elsewhere in the Gulf of Mexico. NOAA Fisheries scientists are conducting research to better understand the whales’ distribution, for example, if they utilize the western Gulf of Mexico and Mexican waters of the southern Gulf of Mexico, and how frequently they may occur in these other areas. The Rice's whale is one of the few types of baleen whales to prefer warmer, tropical waters and that does not make long-distance migrations. They remain in the Gulf of Mexico year-round.
Based on information from closely-related Bryde’s whales, Rice's whales are likely able to reproduce every two to three years, reach sexual maturity at age 9, and mate year-round. Based on data from closely related Bryde’s whales, Rice’s whales may be pregnant for 10 to 12 months, and calves may nurse up to 12 months.
The Rice's whale’s very small population size and limited distribution increase its vulnerability to threats. The most significant threats they face are energy exploration and development, oil spills and spill response, vessel strikes, ocean noise, ocean debris, aquaculture, and entanglement in fishing gear. 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
Vessel strikes can injure or kill Rice's whales. The northern Gulf of Mexico experiences a high amount of vessel traffic where several commercial shipping lanes cross through Rice’s whale habitat. In 2009, a female Rice'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. NOAA Fisheries 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 Rice’s whales spend 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 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 Rice’s whales. It is likely that the Rice's whales rely on their hearing to perform critical life functions such as communication, navigation, finding a mate, locating prey, and predator avoidance. As ocean noise levels increase, the resulting habitat degradation and disruption to these life functions can result in adverse physical and behavioral effects to Rice's whales.
Energy Exploration and Development
The Gulf of Mexico is highly industrialized due to expansive oil energy exploration and production that requires seismic surveys, drilling rigs, platforms, cables, pipelines, and vessel support, and in the future, it may also have wind energy development. Habitat in the north-central and western Gulf of Mexico, which likely includes the Rice's whales’ historical range, has already been substantially modified by the presence of thousands of oil and gas platforms and underwater pipelines. These activities also increase risk of vessel strike from support vessels 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 coat the baleen that the Rice'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 (through inhalation), increased vulnerability to other diseases and infections (through ingestion), and irritation of the skin or sensitive tissue in the whale’s eyes and mouths (through absorption). Additionally, exposure to oil spills can have reproductive impacts.
Chemicals used to respond to oil spills, called dispersants, may also be toxic to Rice’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 negatively affected Rice's whales. While the Deepwater Horizon platform was located outside Rice'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.
Fisheries and Aquaculture Interactions
Like all large whale species, Rice’s whales can become entangled in fishing and aquaculture gear, which can cause serious injuries and even death. Historically, two Rice's whales stranded, entangled with fishing gear. Since 2003, there have been no known serious injuries or mortalities of Rice's whales due to interactions with fisheries. However, their primary habitat overlaps with several commercial fisheries and their foraging behavior may place them at risk for becoming entangled in certain types of gear. Aquaculture activities have largely been absent from their known habitat; however, that may change in the future as this industry is beginning to expand. NOAA’s Aquaculture Program has identified the Gulf of Mexico as one of the first regions for focused evaluation to find Aquaculture Opportunity Areas. In areas where Bryde’s whales (close relatives of Rice’s whales) and aquaculture gear overlap (e.g., New Zealand), entanglements of whales in aquaculture gear have occurred and led to mortality. Aquaculture activities also increase risk of vessel strike from support vessels, add noise to the environment from vessel traffic, may affect water quality, and attract predators.
Ocean Debris
Rice's whales are also at risk from ocean debris. For example, in 2019 a male Rice's whale washed up along Sandy Key in the Florida Everglades with a hard piece of plastic in its stomach, which is thought to have contributed to its death. Plastic often ends up in the stomachs of marine wildlife, though it is often difficult to determine if it was indeed the cause of death for stranded animals.
Small Population Size and Limited Distribution
The Rice's whale’s very small population size and limited distribution increase its vulnerability to inbreeding (offspring may have traits that put the individual at risk), environmental change, decreased disease resistance, and habitat loss. Due to their limited distribution, these whales are vulnerable to catastrophic events that impact their core habitat, while even the loss of a single individual could prevent recovery due to the very small population size.
