By: PhD. Jorge Acevedo Ramírez, CEQUA Foundation researcher.
The Rice’s whale (Balaenoptera ricei) is a new species of whale that was recently described in Marine Mammal Science by a group of researchers from the United States and Japan.
It is surprising that despite the fact that whales are the largest group of mammals on the planet, new species are still being found in the 21st century. The previous new whale species to be described was the Omura’s whale (Balaenoptera omurai) in 2003. However, it should also be noted, as the authors do, that cetacean taxonomy and systematics, even today, remain in constant change. In fact, another previous publication as early as 2017 concluded that, of the currently recognized taxa in cetaceans, 32% have a high probability of misclassification errors and that an accurate taxonomy may contain twice as many currently recognized subspecies.
Thus, for example, one species of killer whale (Orcinus orca) is currently recognized in Antarctic waters but differentiated into three ecotypes. However, recent studies have suggested that these ecotypes may correspond to subspecies or even new unrecognized species. The same situation occurs with the minke whale. There are two species currently recognized, the Antarctic minke whale in the southern hemisphere and the common minke whale distributed globally but represented with a subspecies in the southern hemisphere that is still under debate. The same happens with blue whales, the largest mammal in the world, some subspecies are recognized, and others are still under debate, as is the case of the Chilean blue whale, which could be a new subspecies or even a new species.
All these potential new subspecies or species of cetaceans not yet officially recognized which are still a matter of study and debate among specialists are mainly due to the problems encountered when trying to address taxonomical questions, which include difficulties in obtaining skulls or tissue samples from elusive, often remote and difficult to sample taxa, along with the legal protections afforded to them at the international and national levels. Due to these difficulties, studies often have insufficient samples and/or inadequate geographic sampling of these species that typically have wide distributions and, as a result, sound taxonomic inference is often severely hampered.
Circling back to the Rice’s whale, the new species were considered to be Bryde’s whales, another taxonomic complex of which a single species with two subspecies is recognized, even though there are multiple lines of evidence for both subspecies to be differentiated into different species, the Eden whale and Bryde’s whale. It is from this same taxonomic complex that the description of the Omura’s whale emerged, and it was recognized as a species distinct from the Bryde’s complex in 2003. The first hint that the Rice’s whale might be a different species came from genetic studies conducted on skin samples collected from a group of whales (thought to be Bryde’s whales at the time) in the Gulf of Mexico in 2014. Their results showed the existence of an evolutionary genetic lineage distinct from Bryde’s whales. However, at that time there was a lack of morphometric evidence and a type specimen (holotype) to comply with taxonomic rules, i.e., there was no complete skull and skeleton available from which to describe the animal. It took five more years before an adult male of the possibly new whale was collected due to a stranding in January 2019. Its entire body was recovered off the coast of Florida, USA. Since that time, genetic evidence along with skull morphometrics, as well as distribution data (sightings and strandings) of probable Bryde’s whales in the Gulf of Mexico were re-examined and the conclusion was unequivocal: these Bryde’s whales were actually a new species of whale.
As of the date of the study published in January of this year, Rice’s whales were year-round residents and had very restricted distribution along the continental shelf slope near the De Soto submarine canyon area in the northeastern Gulf of Mexico.
Source: El Pingüino