new sub-species dolphinTursiops truncatus nuuanu
© NOAA/NMFS/SWFSCThe new common bottlenose dolphin subspecies, known as the Eastern Tropical Pacific bottlenose dolphin (Tursiops truncatus nuuanu). This subspecies is smaller than other common bottlenose dolphins.
A new subspecies of common bottlenose dolphin found only in the tropical regions of the eastern Pacific Ocean has been identified by researchers.

An analysis of several specimens conducted by Ana Costa — a marine researcher with the Rosenstiel School of Marine, Atmospheric, and Earth Science at the University of Miami — and colleagues found that the new subspecies is smaller than other common bottlenose dolphins.

In a study published in the Journal of Mammalian Evolution, the scientists named the new subspecies the Eastern Tropical Pacific (ETP) bottlenose dolphin, or Tursiops truncatus nuuanu in scientific terms.

Common bottlenose dolphins are found in temperate, subtropical, and tropical oceans around the world, with the global population estimated to number around 600,000 individuals.

These dolphins, which are highly intelligent creatures, grow to between 6.5 and 13 feet in length, and can weigh more than 1,000 pounds. Their name is a reference to their short, thick snout, or rostrum.

While the common bottlenose dolphin is considered a single species (Tursiops truncatus), in some locations, scientists have observed distinct populations that have differing ecological and habitat preferences.

Costa told Newsweek these distinct preferences can lead to differences in genetics or form, potentially separating populations found in the same region into what scientists call ecotypes (a distinct population of a species that is adapted to local conditions) and even leading to speciation — the evolutionary process by which populations evolve to become distinct species.

For example, Costa and her colleagues from the National Oceanic and Atmospheric Administration (NOAA) — Patricia Rosel with the Southeast Fisheries Science Center (SEFSC) and Eric Archer with the Southwest Fisheries Science Center (SWFSC) — showed in previous research that two ecotypes of bottlenose dolphin that live along the U.S. Atlantic coast were different enough when it comes to genetics and form to be described as distinct species.

Based on their findings, the scientists proposed that one ecotype of the U.S. Atlantic bottlenose dolphin, which prefers shallow waters, be recognized as a new species, Tursiops erebennus (Tamanend's bottlenose dolphin), whereas the other, which tends to be found in deeper, offshore waters, continue to be referred to as the globally distributed Tursiops truncatus (common bottlenose dolphin).

Along the U.S. Pacific coast, more specifically along the coast of California, two common bottlenose dolphin ecotypes have been identified, Costa said. Previous studies in the eastern Pacific Ocean, including in California, revealed differentiation between common bottlenose dolphin populations. However, these were conducted in localized areas.

A distinct form of bottlenose dolphin was also suggested for the eastern tropical Pacific in the early 1900s, but it was based on only a few specimens and field records, according to the researcher.

"Thus, despite the previous studies in the area, there was a need to better characterize the level of differentiation between these different populations and determine whether there was, in fact, a distinct bottlenose dolphin form in the eastern tropical Pacific," Costa said.

In order to do this, Costa, Rosel and Archer collaborated with the late researcher William Perrin at the SWFSC, who passed away in July this year, to conduct a broader study with the aim of better understanding the taxonomy of common bottlenose dolphins in this region.

For the Mammalian Evolution paper, the researchers examined the skulls of more than 130 bottlenose dolphin specimens from both the eastern Pacific and western North Pacific — off the shores of Japan — that are held in museum collections across the United States. In some cases, the team also looked at the total body length of these specimens.
new sub-species bottlenose dolphin
© NOAA/NMFS/SWFSCA pair of Eastern Tropical Pacific (ETP) bottlenose dolphins. These dolphins likely have a preference for deeper, offshore waters between southern Baja California and the Galápagos Islands.
Their analysis revealed significant differences in form among the bottlenose dolphins from the Pacific, observing two distinct clusters.

"The bottlenose dolphins found in offshore waters of the eastern tropical Pacific formed one single cluster, and they were significantly smaller — based on skull and body length — than common bottlenose dolphins forming the other cluster," Costa said. "Our findings indicated that the offshore bottlenose dolphins of the eastern tropical Pacific are speciating from the globally distributed common bottlenose dolphins and should be described as a different subspecies."

The new subspecies is restricted to the eastern tropical Pacific, and likely has a preference for deeper, offshore waters between southern Baja California and the Galápagos Islands.

Costa said the differentiation of the ETP bottlenose dolphins from other common bottlenose dolphins could be the result of the environment they occupy. For example, the distinct environmental conditions in the eastern tropical Pacific and potential variations in feeding behaviors may be influencing the differentiation.

"The specimens in this subspecies are one of the smallest common bottlenose dolphins found," Costa said. "Dolphins are a charismatic fauna, and it is common for the public to think that all dolphin species are already known. However, with the improvement of technologies and integration of different methodologies, as well as the increase in samples from different areas, greater biodiversity has been revealed in more recent years."

The results of the latest study could have have implications when it comes to protecting these animals.

"By better understanding the biodiversity in the ocean, we can better understand the relationship of the dolphins with their environment and the threats they face, and in this way better define conservation and management strategies," Costa said.