The Never-Ending Rise and Fall of Marine Mammals in the North Pacific

Steller sea lions, northern fur seals and harbor seals have declined to critically low numbers in Alaska since the late 1970s.  Some populations such as sea lions now number only about 20% of those that were present when the first biological censuses were conducted in the 1950s.  Unfortunately, biological data do not extend back far enough in time to resolve whether or not the seal and sea lion declines are part of a natural long-term cycle or whether they are the result of fishing and other human actions. One means of pushing the biological information window back beyond the modern day is with data and records from oceanographic, archeological and anthropological studies.  Similarly, insights into the functioning of the North Pacific ecosystem and the evolutionary adaptability of marine mammals to ecosystem change can be gained by combining data from field observations, mathematical models, and captive feeding studies.  Combining such information across multiple disciplines shows that the dramatic declines and increases in seals and sea lions have occurred repeatedly across the Pacific Rim in the absence of industrialized fishing, and that the marine ecosystems of the North Pacific may regularly shift to alternative states every 40-50 years. This has important implications for fisheries management and the conservation of marine life in the North Pacific.