MEPS 244:265-283 (2002)  -  doi:10.3354/meps244265

ABSTRACT: Interannual variability of the physical environment in the eastern tropical Pacific Ocean (ETP) and biological effects of this variability are reviewed and compared to variability in the northeastern Pacific. El Niño Southern Oscillation (ENSO) scale variability of 2 to 7 yr periods is dominant in the eastern equatorial Pacific and decadal scale variability of 10 to 30 yr periods is dominant in the northeastern Pacific. In the eastern Pacific warm pool at the center of the ETP, temporal variability at any scale is relatively low. ENSO warm (El Niño) and cold (La Niña) events have had a variety of effects on marine populations and ecosystems, but these effects are generally followed by recovery within a few years. El Niño effects such as mortality or reproductive failure are most severe on populations dependent on local feeding or breeding grounds in coastal waters or around islands. Decadal variability has also caused change in populations and ecosystems. Most of these effects have been observed in the California Current, Gulf of Alaska, and other well studied regions of the Pacific. The 1976-1977 phase change or Œregime shift¹ is the most well known case of decadal variability. It affected the physical environment throughout the Pacific Ocean and had major effects on North Pacific ecosystems. No regime shift has been detected in the ETP since 1977. However, ENSO variability continues, an unusually persistent warming prevailed in the early 1990s and the thermocline has shoaled in the ETP warm pool area since 1980. Potential population effects on dolphin stocks are discussed. Interaction of environmental changes with other factors, such as fishery stress or mortality, may also induce population effects.

KEY WORDS: Eastern tropical Pacific Ocean · Decadal variability · ENSO · Climate change · Regime shift