Listening to a New Species, the Rice’s Whale, to Support its Conservation

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Rice’s Whale Passive Acoustic Projects

The Rice’s whale is one of the most endangered whale species in the world; its population is estimated at fewer than 100 individuals. The Rice’s whale was first recognized as a new species in 2021. What little is known about these whales primarily was learned from studies in their core habitat along the northeastern Gulf of Mexico shelf break. 

With high levels of industrial activities occurring in the Gulf of Mexico, there are numerous potential threats to these whales. Threats include vessel collisions, oil spill impacts, noise impacts, and fishery entanglements. 

We need to learn more about Rice’s whales and their ecology so that managers can reduce potential impacts of human activities on these whales. Scientists at the Southeast Fisheries Science Center use passive acoustic monitoring to learn more about these whales and where and when they can be found.

Call Repertoire and Behavior

To use autonomous passive acoustic methods to study whales, we need to know what sounds the animals make. From 2015–2019, we conducted vessel-based surveys of Rice’s whales using visual monitoring, sonobuoy surveys, and acoustic tag deployments. 

With sonobuoys, we were able to localize sounds detected in the Rice’s whale habitat. We then approached that area by ship to visually identify Rice’s whales as the source of previously described long-moan calls and tonal-sequence calls. The known call repertoire of Rice’s whales now includes downsweep-sequence calls, long-moan calls, and tonal-sequence calls. Autonomous passive acoustic methods can use this knowledge to detect Rice’s whales in studies of their occurrence and distribution. 

Using Acousonde™ tags, we detected sequences of lower-frequency downsweep pulses, which may represent a fourth call type produced by Rice’s whales. Tag deployments also provided information about their dive behavior that is important for understanding foraging and human threats. Kinematics data showed a diel dive pattern with whales foraging at depths of 200 meters or more (near the seafloor) during the day and resting near the surface at night. These results suggest the whales may be at risk for impacts from vessel collisions and entanglement in commercial fishery gear.

Audio file of downsweep sequence

Note: The audio has been sped up 1.25x to enable the human listener to better hear the very low-frequency sounds.

Audio file of long-moan call

Note: Audio has been sped up 1.25x to enable the human listener to better hear the very low-frequency sounds.

Rice’s Whales in Their Core Habitat

The primary area where Rice’s whales are found in the Gulf of Mexico is known as their core habitat. As part of two projects funded by the U.S. Navy, we have been using moored passive acoustic recorders to understand their occurrence and seasonal use of this important habitat area.

Since the Deepwater Horizon oil spill in 2010, the Southeast Center and Scripps Institution of Oceanography researchers have been deploying HARPs at two sites: site DC near the center of the core habitat and site MP on the northern edge. Our scientists are evaluating the occurrence of Rice’s whale long-moan and downsweep-sequence calls in 10 years of data recordings from these two sites. These will help us to understand whether the whales are found in this habitat year round and whether they have seasonal or interannual cycles to their presence in this area.

Expanding on these studies, Southeast Fisheries Science Center researchers deployed a large-scale sparse array of moored SoundTrap^TM recorders in May 2021, nearly covering the core habitat. We hope to better understand how Rice’s whales use the habitat over time, including seasonal movement patterns within the area. This will help us understand where and when Rice’s whales may overlap with human activities that may pose a threat to them. This information will be crucial for developing management actions to improve conservation and recovery of these endangered whales.

Rice’s Whale Distribution Beyond the Core Habitat

Historical whaling records suggest baleen whales—most likely Rice’s whales—were found throughout a broader area of the Gulf of Mexico than the northeastern core habitat where they are primarily found today. While historical whaling records documented whales in the north-central and southern Gulf, sightings beyond the core habitat are now rare, even with substantial survey effort throughout the northwestern and north-central Gulf. Understanding whether and how often Rice’s whales may currently occur in Gulf waters beyond the core habitat is important for their conservation, considering the high levels of industrial activity in the northwestern Gulf of Mexico.

We want to understand the extent of their distribution in the northern Gulf of Mexico and whether they exhibit seasonal movements throughout this range. We are using long-term passive acoustic recorders to investigate whether Rice’s whales occur along the northwestern and north-central Gulf shelf break. In recordings collected from the northwestern Gulf during 2016–2017, we discovered new variations of the stereotyped long-moan calls produced by Rice’s whales. These calls were detected most commonly at the westernmost site (WF on the map) on as many as 16 percent of days (or 1 in 6 days). This evidence shows that some Rice’s whales persistently occur beyond the core habitat. It also suggests that they may be less common in the northwestern Gulf than in the northeastern Gulf core habitat.

Audio file of long-moan call variant from the northwestern Gulf of Mexico 

Note: The audio has been sped up 1.25x to enable the listener to better hear the very low-frequency sounds.

This new knowledge of their occurrence beyond the core habitat will help managers to develop recovery plans for their conservation. However, there is still a lot we do not know about the distribution of Rice’s whales throughout the entire Gulf of Mexico. Do they still occur in the southern Gulf of Mexico? Do they occur in deeper waters beyond the shelf break? Scientists at the Southeast Fisheries Science Center are now deploying long-term passive acoustic recorders throughout the Gulf of Mexico to answer these questions and understand whether they have a broader distribution than is currently known. This information will help managers protect them throughout their range.

More Information

• Frequently Asked Questions—Rice’s Whales
• Call Variation and Occurrence Beyond the Known Core Habitat
• Acoustic localization, validation, and characterization of Rice's whale calls
• Spatial Distribution and Dive Behavior of Gulf of Mexico Bryde's Whales: Potential Risk of Vessel Strikes and Fisheries Interactions
• A New Species of Baleen Whale (Balaenoptera) from the Gulf of Mexico, with a Review of its Geographic Distribution
• Marine Mammal and Turtle Division
• Southeast Fisheries Science Center