Apex marine predator declines ninety percent in association with changing oceanic climate

Abstract

Three time series of pelagic bird abundance collected in disparate portions of the California Current reveal a 90% decline in Sooty Shearwater (Puffinus griseus) abundance between 1987 and 1994. This decline is negatively correlated with a concurrent rise in sea‐surface temperatures; Sooty Shearwaters have declined while sea temperatures have risen. There is a nine‐month lag in the response by shearwaters to changing temperatures. The geographical scale of our study demonstrates that the decline of Sooty Shearwaters is not a localized phenomenon, nor can it be ascribed to a short‐term distributional shift. The Sooty Shearwater is the numerically dominant species of the California Current System (CCS) in summer (austral winter), with an estimated population in the late 1970s of 5 million individuals. If the observed warming of the waters of the California Current System is an irreversible manifestation of a changing global climate, then the impact upon Sooty Shearwater populations seems likely to be profound.

Physical and biological variables affecting seabird distributions during the upwelling season of the northern California Current

“…Perhaps it was related to the fact that the Briggs et al study occurred at the beginning of a warm Pacific Decadal Oscillation (PDO) period, 1976-1998(Mantua and Hare, 2002, when all populations in the region were robust, as opposed to our study, which occurred at the end of the long warm-phase decline that followed (e.g. Veit et al 1997). This issue is discussed further below.…”

“…Our estimates, with the exception of the slope habitat, were similar and resulted in nearly an identical total (May: 45.0, 32.0, and 2.3 kg km -2 ; total = 79.3 kg km -2 ). Given that the Sooty Shearwater, by far the most abundant species in the CCS (and which contributes immensely to overall biomass), declined by 90 % in the CCS since 1976 (Veit et al, 1997;Oedekoven et al 2001;Ainley and Divoky, 2001), our results are surprising. We expected to encounter significantly fewer numbers and biomass than was present, as we have noted in central California studies (e.g., Oedekoven et al, 2001).…”

“…Therefore, community structure and composition are well known, and areas of concentration have been identified, as have some of the larger-scale oceanographic features (fronts) to which seabird occurrence patterns are correlated. Also identified have been trends that show short-term (El Nino-Southern Oscillation) and longer-term climatic influences (climate oscillations) (Veit et al, 1997, Ainley andDivoky, 2001). While some of the oceanographic processes that affect seabird abundance and distribution in the CCS have been identified, this area of research has not in the least been exhausted.…”

The detection of climate impacts: some methodological considerations

“…Less than 10 years of results have been used in many published studies (e.g. Veit et al, 1997;Koontz et al, 2001;Martin, 2001;Orlandi et al, 2002;Sergio, 2003;Sainio et al, 2004) and 8 years have been used as a minimum series length to qualify as 'long-term' (e.g. Wiens, 1984;Houlahan et al, 2000).…”

Sandy bottom communities at the end of a cold (1971-1975) and warm (1997-1998) regime in the California Current: impacts of high and low plankton production

“…The Pacific Decadal Oscillation describes these interdecadal shifts in climate variation Hare 2002, Mantua et al 1997), which Chavez et al (2003) call El Viejo, an excellent contrast to the more frequent El Niño-Southern Oscillation (ENSO). El Viejo caused often abrupt changes in marine ecosystems that are best documented in fisheries and plankton, but also birds and mammals (e.g., Roemmich and McGowan 1995, Brodeur et al 1996, Mantua et al 1997, Veit et al 1997, Francis et al 1998, McGowan et al 1998, Anderson and Piatt 1999, Beamish et al 1999, Mackas and Tsuda 1999, Vandenbosch 2000, Chavez et al 2003. Warm regimes in the California Current are characterized by sharper thermoclines, greater stratification, less mixing of deep, nutrient-rich waters into the photic zone, and lower planktonic production.…”