In 2005, Southern Resident Killer Whales or Orcas were listed as endangered species. Reasons cited included depleted prey, contaminants, and disturbance from vessel traffic and sound. Noise from vessels, military activities, and industrial activities interrupts the Orcas’ ability to use sound for hunting and communications. Now there is a new threat to the survival of Southern Resident Orcas.
Recent studies by NOAA (US National Oceanic and Atmospheric Administration) Northwest Fisheries Science Center, Scientists from China, and the North Gulf Oceanic Society based in Alaska have determined that inbreeding among small groups of Southern Resident Orcas is detrimental. Due to inbreeding, this species continues to suffer lower birth and survival rates. Findings from these studies indicate that individuals who are highly inbred are much less likely to survive through their reproductive years.
Female Orcas take about 15 years to reach peak fertility and give birth to a single calf. In some populations, birth takes place only every 5 years. Scientists are concerned that Southern Resident Orcas might not live long enough to ensure the growth of their population. It is believed that if the population remains both genetically isolated and small, inbreeding will most likely be an even bigger threat to the population.
There are three main types of Killer Whales or Orcas in the North Pacific: Resident, Transient, and Offshore. Resident Orcas are the most commonly sighted of the three populations. Southern Resident Orcas are the smallest of four Resident communities within the North Pacific and are the most at-risk. Despite our efforts to control their environment, intrinsic genetic factors may be the real key to success. Inbreeding appears to affect the population’s fitness, limiting growth. Fewer than 80 Southern Resident Orcas remain. Interestingly, the genetic threat has not been observed in other North Pacific Orcas, and the population within these groups is increasing.
NOAA Photo
