Laugan Miller

Jim Spickard

Research Methods

3/31/19

Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems

This research looks at the relationship between sea urchins, sea otters, and killer whales in Alaska. This was important to look at because recently sea otters have been declining in Alaska. The birth rates of sea otter’s in these locations is equal to that of sea otters found in stable environments. This means there must be increased mortality rates to justify the declining populations of sea otters. Researchers ruled out migration because there were no new sea otter populations and ruled out disease because this would have been seen by dead carcasses washing up on the beach. The research looked at three key points of evidence leading to their results which was that the decline in sea otter populations was due to increased predation on sea otters. Calculations showed that this otter decline could have been due to just 3.7 whales. The most likely shift of killer whales preying on sea otters is due to the killer whales losing a prey item. Some prey items of killer whales include stellar sea lions and harbor seals and these species have both had a decline in populations since the 1970s. The relationship between sea otter populations and the collapse of kelp are most likely caused by the offshore oceanic realm. This changed the system from a three level trophic system to a four level trophic system which means sea otters were no longer the top predator. This freed sea urchin populations to expand. This article was helpful to my research because I know that I not only have to look at possible predators of sea urchins but their possible predators and what would cause them to shift to eating sea urchins.

Estes, J. A., et al. “Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems.” Science, American Association for the Advancement of Science, 16 Oct. 1998, science.sciencemag.org/content/282/5388/473.