Rice’s whales (Balaenoptera ricei) are a relatively newly distinguished species of baleen whale. Previously thought to be a subpopulation of Bryde’s whales (Balaenoptera edeni and Balaenoptera brydei), genetic and skeletal differences that distinguished them as their own species were discovered in 2021. Despite its recent discovery, this species has been far from untouched by anthropogenic activity and with less than 100 individuals remaining it is Critically Endangered. Rice’s whales are the only year-round resident baleen whale in the GOM. At the time of their discovery, they were thought to reside only off the shelf break in the northeastern Gulf off the coasts of Florida and Alabama, however later through passive acoustic monitoring, they were discovered to reside also in the northwestern Gulf. The continental shelf regions of the Gulf contain large amounts of natural resources including oil and natural gas. For decades, these resource deposits in the Gulf of Mexico have sustained life in the United States. Rice’s whales are heavily threatened by this activity in the Gulf, and their feeding, mating, and navigation abilities are disrupted by noise from vessels and oil drilling sites. They are also at risk of vessel strikes and entanglement in boating and fishing gear, as well as ingestion of pollution and debris.

Since many whales are migratory species, Rice’s whales residing year-round in the GOM prompts the question of possible migration within the Gulf. The possibility of east-west migration in the Gulf is important to understand because the majority of anthropogenic activity takes place in the western Gulf. Increased understanding of spatiotemporal occurrence patterns, such as seasonal movements between the east and west, could help researchers and conservationists find ways to better protect the few remaining individuals. 

In order to monitor the presence of Rice’s whales across the GOM shelf, researchers use passive acoustic underwater frequency recording systems called HARP (High-frequency Acoustic Recording Package). HARP is an underwater recording system that records frequencies and condenses them into snapshots or graphs that can then be interpreted. The anatomy of these packages includes batteries and data disks in cylinders. Weights counteract the buoys to keep the package anchored on the seafloor, and other floats raise the rope and the hydrophone upwards in the water column. The hydrophone, raised up along the rope, records sounds from 10 Hz to 100 kHz. When the HARP needs to be retrieved, the boat sends a signal which causes the floats to release and brings the whole device to the surface. One challenge with interpreting the HARP data is that it includes vocalizations from all animals, ambient sounds, and human-generated noises, such as ships and sonar, are all recorded as well as Rice’s whales calls.

Another challenge faced in the monitoring of Rice’s whales’ calls, is recognizing the patterns of the calls on the frequency graphs because of the lack of knowledge of the unique types of Rice’s whales’ calls. Therefore, in order to verify possible Rice’s whales’ calls recorded at the HARP sites in the NW GOM, the data was compared to the graphs of known Rice’s whales’ long-moan calls detected in the NE GOM (their originally known habitat location). The structure of the Rice’s whale’s long-moan  call has 3 parts: The start tone, transition zone, and tonal tail, which are defined based on the changes in frequency at certain intervals of time. In order to be classified as an official variant of the Rice’s whale’s long-moan call, they must be detected a repeated number of times and with slight variations.

Through the use of passive acoustic surveillance technology, researchers have learned that Rice’s whales do live along the shelfbreak of the NW Gulf, and, as a byproduct of these investigations (Soldevilla et.al), 6 variations of the Rice’s whale long-moan call were discovered. Based on the results of the studies however, further research is needed to answer the question of east-west migration. Based on the current knowledge and continuing findings of this species, the next steps towards their protection would include further research to answer the questions of migration habits, true population numbers, and spatial density. Through these research methods and other methods like satellite tagging, proof of Rice’s whales existing in the western Gulf of Mexico requires the designation of critical habitat, and therefore a protection plan, which will help preserve one of the most endangered species of whales.