Nearly four decades ago, a lone voice echoed through the Pacific, emitting a unique song at a frequency of 52 Hertz. This enigmatic sound puzzled those who listened, as it was significantly higher than the vocalizations of blue whales or their cousins, the fin whales. The mystery of Whale 52, as it came to be known, has continued to intrigue scientists, who have been studying its calls for years.

Despite numerous hearings, Whale 52 has never been seen. Some researchers speculate that it may have a physical deformity that alters its vocalization, while others propose that it could simply be a whale with an unusually high-pitched voice. However, marine biologist John Calambokidis of the Cascadia Research Collective suggests another possibility: Whale 52 may not be an anomaly, but rather a clue to a larger phenomenon. Calambokidis has spent over 50 years studying cetaceans and believes that Whale 52 could be a hybrid, part blue whale and part fin whale.

The existence of such a creature, known as a flue whale, is becoming increasingly common as warming seas push blue whales into new breeding grounds, where they are more likely to mate with fin whales. A recent survey of north Atlantic blues found that fin whale DNA comprised up to 3.5% of their genome, a surprising figure given that the two species diverged 8.35 million years ago. If Whale 52 is indeed a hybrid, its presence suggests that genetic intermingling between blue whales and fin whales has been occurring for decades, if not longer.

Hybridization among cetaceans has been documented before, notably between narwhals and belugas, as well as between two species of pilot whales. However, this phenomenon is not well understood in marine mammals, and little is known about its implications for the genetics, behavior, and survival of these animals. Calambokidis notes that blue whales are still struggling to recover from centuries of whaling, with some populations remaining at less than 5% of their historical numbers.

The discovery of hybrids like Whale 52 has significant implications for conservation efforts. If these animals are not easily identifiable, it could lead to inaccurate estimates of the blue whale population and difficulties in assessing the efficacy of conservation programs. Moreover, sterile hybrids cannot contribute to the survival of their species, posing a threat to their long-term viability. “If it becomes frequent enough, hybrid genomes could eventually swamp out the true blue whale genomes,” said Aimee Lang, a marine mammal geneticist at the National Oceanic and Atmospheric Administration.

The phenomenon of hybridization also has broader implications for marine ecosystems. Each whale species plays a specific role in maintaining the health of these ecosystems, and hybrids that do not fulfill this role can undermine the delicate balance of the sea. “Those individuals and their offspring aren’t fully filling the ecological niche of either parent species,” Calambokidis explained.

The uncertainty surrounding hybridization is further complicated by the upheavals already underway in marine ecosystems. Many of these ecosystems are experiencing regime shifts, driven by warming waters, acidification, and shifting prey distributions. These changes are pushing some cetacean species into smaller, more isolated breeding pools, increasing the likelihood of interbreeding and hybridization.

The concerns surrounding hybridization extend beyond blue whales. Rampant interbreeding among the critically endangered Southern Resident killer whale population, for example, is cutting their lifespans nearly in half. Similarly, the 370 North Atlantic right whales that remain may face similar challenges. While some level of cetacean interbreeding and hybridization may be inevitable as species adapt to climate change, the real concern is whether these changes will outpace the ability of whales to survive.

“There are examples of populations that are doing well, even though they have low genetic diversity, and there are examples where they aren’t doing well,” said Vania Rivera Leon, a researcher at the Center for Coastal Studies. “They might be all right under current conditions, but if and when the conditions shift more, that could flip.” The effects of hybridization can unfold gradually, making it difficult for humans to perceive the changes quickly. Unlike fish, which have rapid life cycles, whales live for decades, with overlapping generations that obscure immediate trends.

To truly grasp the impacts of hybridization on whale populations, researchers may need to study these animals for extended periods, possibly twice the time that has passed since whaling largely ceased. The story of Whale 52 serves as a reminder of the complexities and uncertainties surrounding the world’s oceans and the creatures that inhabit them. As scientists continue to probe the genetic signatures of whales worldwide, they hope to distinguish whether hybridization is an emerging trend driven by climate change or a long-standing, overlooked facet of cetacean evolution.

This article originally appeared in Grist at https://grist.org/oceans/what-the-worlds-loneliest-whale-may-be-telling-us-about-climate-change/. Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and a just future. Learn more at Grist.org.