Did Commercial Whaling Cause the Sequential Decline of Marine Mammals in Alaska?

Defense Date

12-2011

Document Type

Capstone

Degree Name

M.S. Marine Biology

First Advisor

Edward Keith

Second Advisor

Amy C. Hirons

Abstract

The killer whale (Orcinus orca) is an apex predator that, according to its feeding habits, may be described as a resident, a transient, or an offshore type in the Pacific Ocean. There is an ongoing debate about anthropogenic impacts on the dynamics of the North Pacific food web; impacts such as the development of commercial whaling and the effects on the diets of apex predators. This paper reviews two main hypotheses; first that the decimation of the great whales caused transient killer whales to cease hunting large whales to hunt smaller marine mammals. The alternate hypothesis states that great whales were never a main prey item for transient killer whales and therefore their decimation did not cause prey-switching, or the population collapse of small marine mammals. Evidence is presented in the form of observed attacks on great whales, isotope records that showed enrichment of nitrogen 15N/14N and carbon 13C/12C among types of killer whales, and physiological evidence. The alternative hypothesis was supported by the physical challenges whales would have to endure to hunt greater whales, “regime shifts,” in the North Pacific and ecological changes. Additional information includes descriptions of types of killer whales, food webs, whaling history, marine mammals of Alaska, and population numbers. This paper concludes that although killer whales are one of a number of contributing factors in de disappearance of seals, sea lions, and sea otters in Alaska, commercial whaling does not appear to be the key that unleashed a cascade of population declines.

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