Environmental change in the eastern tropical Pacific Ocean: review of ENSO and decadal variability. Fiedler, P. C..
Marine Ecology Progress Series:
2002
Notes
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 Nino 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 Nino) and cold (La Nina) 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 Nino 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 'regime shift' 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.
Variable responses of seabirds to change in marine climate: California Current, 1985-1994. Oedekoven, C. S.; Ainley, D. G.; Spear, L. B..
Marine Ecology Progress Series:
2001
Notes
We conducted annual ship-board surveys to determine the density and distribution of seabirds off central California in relation to marine climate, from 1985 to 1994. Summarized here are results for the sooty shearwater Puffinus griseus, the common murre Uria aalge, and Cassin's auklet Ptychoramphus aleuticus, the 3 most abundant seabirds in the central part of the California Current (91% of seabird abundance and biomass). During the study, sea-surface temperature, wind speed and thermocline depth all increased, salinity decreased and thermocline intensity (slope) showed no consistent trend. Periods of cool water and warm water, as well as offshore and inshore excursions of the shelfbreak front, alternated and were mediated by the Southern Oscillation and upwelling intensity. The responses to climate variation by the 3 seabird species were in accord with their respective morphologies and natural history patterns. All moved closer to shore and away from the shelf-break front (which also weakened). Abundance of the shallow-diving shearwater and auklet decreased dramatically, but those of the deeper-diving murre did not. The shearwater, which nests in the southern hemisphere and is the most mobile of the 3 seabirds, likely changed its migration routes and reduced its association with the California Current. The auklet, which breeds within the study area and lacks mobility, declined in number, most likely due to reduced breeding success and subsequent reduced population size. Remaining auklets moved away from the shelfbreak, but not as far inshore as the shearwater. The murre, which also breeds locally, is the most adaptable owing to its deeper-diving capabilities. It shifted distribution within the study area to feed on alternative prey found throughout the water column.
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