Distribution during summer when murre abundance is high is probably determined by local upwelling and current patterns. Densities were highest in the northern region of Monterey Bay, probably due to higher food availability. Water is advected from the southern to the northern portions of the Bay, carried by an eddy of the California Current. Upwelling is centered off of Point Pinos to the South. As recently upwelled, nutrient rich water is transported from south to north, it promotes increased phytoplankton production, which works its way to higher trophic levels as it is carried north. This results in higher prey availability in the north, and thus higher Common Murre density.
The primary effect of the 1982/1983 El Nifio-Southern Oscillation phenomenon was a decrease in primary productivity that lead to a reduced availability of the normally dependable summer prey resources. As a consequence, murres which came into the Bay in June 1983 in large numbers quickly dispersed, resulting in low densities in July and August. Murres that were found in Monterey Bay at this time were thin and fed on a different array of prey items.
This study supports the hypothesis that concentrations of higher trophic level marine predators are concentrated “downstream” from upwelling centers. Peak abundance of murres in Monterey Bay occurred shortly after the seasonal peak in upwelling. During this peak abundance, murres were concentrated in the northern portion of the Bay (Soquel Cove) which is downstream of the upwelling center off of Point Pinos to the south.
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