Two orcas doing most of breeding among dwindling population
SEATTLE — Just two male whales fathered more than half the calves born since 1990 in the population of southern-resident killer whales, a sign of inbreeding, scientists have learned.
“It was a shocker to find out two guys are doing all of the work,” said Ken Balcomb, director of the Center for Whale Research and an author on a paper published this week in the peer-reviewed scientific journal Animal Conservation. The findings are based on a new genetic analysis of the whales that frequent the Salish Sea and Puget Sound.
Already a small population of 76 animals, the southern residents are acting more like a population of only 20 or 30, with few animals breeding, said the lead author, Michael Ford, a conservation biologist at NOAA Fisheries Northwest Fisheries Science Center.
The paper builds on earlier work and raises new questions about whether inbreeding is another factor contributing to the southern residents’ difficulties, Ford said.
“We found kind of a hint of a suggestion that more inbred individuals survive at a lower rate,” Ford said. “But that is uncertain, and we want to understand that better, to learn if there is a negative relationship between being inbred and the probability of survival.”
Scientists discovered through DNA analysis of skin and fecal samples that just two whales, J1 and L41, are the fathers of more than half the other sampled whales born since 1990.
Unlike many other wildlife species, southern-resident killer whales don’t leave their families as they mature to find mates and new territory. They stick together for life — and even breed with family members, scientists have discovered.
Genetic analysis indicates mating occurred between a mother and son in the J pod; a father and daughter in the J pod; half-siblings in the L and K pods, and between an uncle and a half-niece in the L and K pods.
What is most remarkable to him, Balcomb said, isn’t even the inbreeding in the population, but the cratering birthrate, and small number of breeding females among the southern residents.
No babies have been born and survived in the southern residents’ J, K and L pods since 2015, Balcomb said.