Almost all of the orcas born in recent baby boom are male

orca whale

The number of male calves in British Columbia’s southern resident killer whale population could mean trouble for future generations.

The southern resident population consists of 84 whales living in three different pods in the Salish Sea, a network of waterways in southwestern British Columbia and northwestern Washington. Eight calves were born into the population in 2015, which is the most researchers have seen in 40 years. Typically, around three are born each year.

The baby boom was celebrated at first, but now that the Washington-based Centre for Whale Research has confirmed a fifth calf is male, researchers are expressing concern.

“Ideally, you get more or less a 50-50 ratio in the sexes,” scientist Ken Balcomb told Times Colonist. “And that is true of populations that have been studied around the world, and it was true of this population when we began the study 40 years ago.”

In addition to J-54, the fifth whale to be confirmed male, another is suspected to be male, and one is unknown. Only one of the eight calves is confirmed female.

According to Balcomb, male whales won’t breed with animals outside their group. That means the population’s off-balance sex ratio will make it difficult for the whales to reproduce when they reach breeding age, especially since female killer whales only give birth about once every three years.

Researchers are currently looking into why so many of the calves are males, but their best guess so far, is the populations’ exposure to toxic waste from sources like oil spills and agricultural and sewage run off.

“We’re wondering if…that’s affecting the fetus,” Balcomb told reporters.

While more research needs to be done to determine these toxins’ impact, which Balcomb says could take years, they’ve seen similar trends in other marine mammals exposed to toxins, such as seals.

“Sooner or later, we have a problem,” Balcomb said. “And we’re seeing that in the whales.”