Sea Otter Populations: A Case Study

A third threat to the sea otter populations is predation from killer whales. It was observed that in certain areas of Alaska many sea otter populations had been decreasing since the early 1990s. Killer whale predation is believed to be cause of their decline for the following reasons. The first line of reasoning being, an increased number of sightings of attacks on sea otters by killer whales. The first attack was reported in 1991, but since then an additional nine attacks had been reported. From this it was determined that killer whales had been preying on sea otters, since the probability of actually seeing an attack in such a large area was extremely low and a number of attacks had already been seen. Second, it was observed that in areas occupied by killer whales, sea otter populations have been decreasing; whereas in areas inaccessible to killer whales, sea otter populations were constant. Lastly, by extrapolating the number of sea otters that have been killed by killer whales based on the decreasing population rate and comparing it to the observed number of attacks. The results showed that the estimated number, 5.05, was very similar to the observed number, 6, of killer whale attacks over a 6-year period (Estes, et al., 2016). It is estimated that in the Alaskan Aleutian Islands, 40,000 sea otters have been consumed by killer whales; a 95 percent reduction in the population (Garshelis and Johnson, 2013).

This increased predation was caused by a decrease of the killer whale prey populations such as steller sea lions and harbor seals, whose population have plummeted around the same time as the that of the sea otter in the Aleutian Islands (Estes, et al.,