Researchers at the National Oceanographic and Atmospheric Administration said the population of the group formally known as Southern Resident killer whales numbers only about 85 animals and they were listed as endangered under the federal Endangered Species Act in 2005.
DNA testing of the whales that seasonally visit Puget Sound showed some of the progeny studied were the result of matings within the same social subgroups, or pods, that are part of the overall population, a NOAA release said Thursday.
"We were surprised that, in many cases, the father was from the same pod as the mother. Based on earlier studies, we didn't think killer whales mated within their own pod," Michael of NOAA's Northwest Fisheries Science Center in Seattle said.
"This behavior may be unique to the Southern Resident population, perhaps related to the population's small size," Ford said.
Scientists are worried about the group's lack of genetic diversity, which Ford characterized as a "bottleneck."
"Since this population remains isolated from other killer whale populations, mating within pods puts Southern Residents at risk of genetically deteriorating further from a potential increase in inbreeding or harmful mutations," he said.