Genetic evidence shatters prior assumptions, revealing two distinct killer whale species deep in the ... [+]
Orcas, also known as killer whales, are incredible creatures. Their undeniable intelligence, complex social structures, impressive communication skills and collaborative hunting strategies have captured the wonder of humans for centuries.
Despite their name, “killer whales” aren’t true whales–they are, in fact, “oceanic dolphins.” Generally, whales tend to be larger and have more elongated bodies compared to dolphins.
Notable for their streamlined bodies, pronounced beaks and curved dorsal fins, orcas and other ... [+]
Orcas and other oceanic dolphins typically have more streamlined, agile bodies with pronounced beaks and a dorsal fin that is often more prominent and curved. In contrast, many whale species have larger, bulkier bodies with smaller dorsal fins relative to their size.
Orcas are classified into different “ecotypes,” which are populations of the species associated with a specific feeding specialization and lifestyle. These ecotypes have traditionally been considered as subdivisions of just a single globally distributed species, Orcinus orca.
One of the most heated debates among marine biologists is whether two of these ecotypes—the “resident” and Bigg’s (aka “transient”) orcas of the North Pacific—are similar enough to be considered a single species. Today, however, we may be at the cusp of reclassifying these orca populations as two distinct mammal species, according to a recent study published in the journal Royal Society Open Science.
What Are The Differences Between Resident And Transient Orcas?
Phillip Morin, lead author of the paper and evolutionary geneticist at Southwest Fisheries Science Center, said, “We started to ask this question 20 years ago, but we didn’t have much data, and we did not have the tools that we do now.”
After years of meticulous research—with the help of improved tools and more robust data—there is considerable evidence that these majestic creatures comprise two separate species in the North Pacific, both of which are distinct from the widespread Orcinus orca. This finding is particularly interesting given that these orcas have evolved independently despite inhabiting overlapping marine territories of the eastern North Pacific.
Michael Bigg, a Canadian scientist after whom the Bigg’s killer whale is named, first noticed some striking differences between the two groups in the 1970s, the main one being that they never mixed. This is a crucial behavioral distinction that’s often indicative of separate species.
Bigg's killer whale T099, Bella, traveling in Penn Cove Whidbey Island in Coupeville, Washington, ... [+]
In the field, researchers have been able to diagnose the resident and transient killer whales based on morphological differences, such as the shape of their dorsal fins. Resident orcas exhibit a dorsal fin with a more pronounced curvature, giving it a rounded profile. In contrast, transient orcas boast a dorsal fin that is more angular and pointed, resulting in a distinctly sharper silhouette.
The two species also show remarkable differences in hunting strategies and social dynamics. Residents specialize in “piscivory,” which means they primarily feast on fish (like salmon). They also coordinate in family pods that utilize echolocation to track their prey.
On the other hand, transients operate in smaller, more agile groups, focusing their predatory skills on hunting other marine mammals such as whales or seals. These behavioral specializations further emphasize the unique adaptations each group has developed to thrive in their respective ecological niches.
Aside from the ecological and morphological differences, genetic analyses also support the claim of their distinct species status.
Crucially, the study revealed that their genetic distinctiveness indicates limited “gene flow,” meaning there are reproductive barriers preventing interbreeding between these ecotypes over evolutionary time, which ties back to Bigg’s observation in the ‘70s. This lack of gene flow allows differences to accumulate, further widening the divergence between the two species.
The researchers emphasize that previous genetic studies have indicated that the two species diverged over 300,000 years ago and originate from opposite branches of the killer whale family tree, making them among the most genetically distinct ecotypes of killer whales worldwide.
The Significance of Recognizing Orcas As Multiple Species
Separating the North Pacific’s transient and resident orcas into distinct species holds substantial weight. Recognizing them as separate entities allows for targeted conservation efforts.
Strategies can address each species’ specific needs and threats, ensuring more effective protection of their unique ecological requirements and vulnerabilities. This includes habitat protection, prey availability and human activities that impact killer whale populations. Management plans can be tailored to Bigg’s and resident orcas’ distinct behaviors, feeding habits and social structures.
It can also raise public awareness about their diversity and importance in conservation in the eastern North Pacific. This increased awareness can lead to more significant public support for conservation initiatives and efforts to protect these unique populations. Legal frameworks can be updated to reflect this taxonomic revision, providing specific protections for each species.
The team behind the paper has suggested the scientific names Orcinus ater for the resident species and Orcinus rectipinnus for the transient (Bigg’s) species. These proposed scientific names are currently being evaluated by the Taxonomic Committee of the Society for Marine Mammalogy.
