Hybrid Dolphins Raise Red Flags

Off the coast of the small French territory of Mayotte in the Indian Ocean, a revolutionary marvel has scientists reeling with concern for the fate of the local dolphin populations. 

The waters of Mayotte have become home to a hybrid dolphin, with blended traits of the Indo-Pacific bottlenose (Tursiops aduncus) and the Indian Ocean humpback dolphin (Sousa plumbea), according to Earth.org. 

While hybridization of cetacean species is not unheard of, it is extremely uncommon, especially in wild populations. For scientists, the discovery raises red flags about the health of the respective dolphin species, whose populations have collapsed in the last decade. The humpback dolphin population, in particular, is estimated to have only five left in the local lagoon. 

The lagoon off the coast of Mayotte is historically considered a rich, biodiverse waterway, complete with a double barrier reef, 760 species of fish, and at least 22 species of marine mammals. While these species of dolphins typically coexist in this lagoon, their behaviors and social structures are fundamentally different, keeping the Indo-Pacific bottlenose and humpback dolphins biologically independent. The fact that they are interacting enough to mate signifies that their populations are in severe distress, lacking options to breed with their own kind. 

While this phenomenon is often nature's way of building resilience against climate change, hybridization in such instances is particularly concerning for biodiversity. In Australia, a similar problem arose when an endangered frog species began to crossbreed with a more common species. 

If hybrid breeds become more commonplace in the ecosystem, it could wipe out the two vulnerable dolphin breeds they're derived from in the process. Plus, it's unclear if this new species can reproduce given its genetic mix or whether it would be socially accepted in the purebred pods. 

The region alarmingly has no conservation plan in place at present. However, efforts for other cetacean populations around the world – like a landmark lawsuit* to protect the Māui dolphin (Cephalorhynchus hectori maui) – show that when indifference is replaced with action, these species can be preserved.

[*A New Zealand environmental group, represented by Earthjustice and Law of the Wild, filed suit on December 04, 2024 against US fisheries regulators to protect the rarest marine dolphin in the world. The grassroots group, Māui and Hector’s Dolphin Defenders, sought to enforce the US Marine Mammal Protection Act, which requires the US government to ban seafood imports from any foreign fishery that excessively harms marine mammals. The suit was filed in the United States Court of International Trade.

The suit contended that New Zealand fishing fleets were driving the critically endangered Māui dolphin to extinction, with estimates that only approximately 30 to 50 individuals remained worldwide. The fleets operating along the West Coast of New Zealand’s North Island didn’t intentionally catch Māui dolphins, but the marine mammals got caught when fishers targeted commercial seafood species in large nets that hang in the water for days or drag through the sea, scooping up everything in their path. Even if fishers freed dolphins from the nets before they drowned, they could suffer serious health impacts from not being able to surface to breathe because nets confined them. 

“With such a critically low population, the Māui dolphin cannot afford a mistake by the US agencies charged with ensuring that United States actions don’t contribute to its decimation”, said Earthjustice attorney Natalie Barefoot. “The species certainly cannot afford repeated mistakes”.

In 2022, the United States Court of International Trade banned some New Zealand seafood imports to America after the marine-protection group Sea Shepherd filed suit, showing harm to Māui dolphins. Despite the incremental protections put in place since that litigation began, more Māui dolphins had perished in the fishery, and the population continued to decline. 

“Fifty years ago, there were 2,000 Māui dolphins. Since then, the population has plummeted by over 97%. It’s clear we have to take steps to save this species from extinction”, said Earthjustice attorney Sabrina Devereaux. Over the past two decades, the population has declined by roughly 3 to 4% per year. 

“The incremental measures that have been put in place in New Zealand’s fisheries since 2020 have not been enough to pause, let alone reverse, the Māui dolphin’s trend toward extinction”, said Law of the Wild’s Legal Director Brett Sommermeyer. “As a result, those measures are not comparable to the United States’ standards”.

Māui dolphins are highly intelligent. The species has a complex social system, and they typically live in small, tight-knit groups of two to eight individuals. The loss of a single member of one of these groups can disrupt their social dynamic. Māui dolphins’ biology makes them especially vulnerable to human impacts; they live about 25 years, and females don’t reach sexual maturity until around eight years old and produce just one calf every two to four years. 

As the lawsuit pointed out, “Even low levels of human-caused mortality can outpace the population’s natural growth rate, leading to its extinction”].