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Marine Ecology Progress Series

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MEPS 461:257-271 (2012)  -  DOI:

Marine mammal response to interannual variability in Monterey Bay, California

Julia A. Burrows1,2,*, James T. Harvey1, Kelly M. Newton3, Donald A. Croll3, Scott R. Benson4

1Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, California 95039, USA
2Present address: Duke University Marine Laboratory, 135 Duke Marine Lab Rd., Beaufort, North Carolina 28516, USA
3Center for Ocean Health, University of California Santa Cruz, 100 Shaffer Rd., Santa Cruz, California 95060, USA
4Protected Resources Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration c/o Moss Landing Marine Laboratories Norte 7544 Sandholdt Road, Moss Landing, California 95039, USA

ABSTRACT: The coastal upwelling ecosystem near Monterey Bay, California, is a productive yet variable ecosystem and an important foraging area for many mobile apex predators, such as marine mammals. Long-term studies are necessary to better understand how wide-ranging predators respond to temporal environmental variability; however, few of these studies exist. We conducted monthly shipboard line-transect surveys in Monterey Bay from 1997 to 2007. We identified 22 species of marine mammals, and calculated monthly and annual densities for the 12 most commonly sighted (focal) species. Species richness remained relatively constant (mean richness ± SE: 13.7 ± 0.396 species yr−1) from 1997 to 2006. Focal species were most evenly distributed (Shannon’s equitability, EH = 0.820) but least dense (mean density ± SE: 0.0598 ± 0.0141) during the anomalous upwelling conditions of 2005, and least even (1997 EH = 0.413; 1998 EH = 0.407) but dense (mean density ± SE: 1997: 0.433 ± 0.177; 1998: 0.438 ± 0.169 ind. km–2) during the 1997/1998 El Niño event. There were no statistically significant differences in the densities of marine mammal species between warmer and cooler years. The community and species-specific responses of marine mammals to warm-water years differed depending on the mechanism of oceanographic variability. During the 1997/1998 El Niño (a basin-wide event), marine mammals aggregated in nearshore areas, such as Monterey Bay, with relatively greater productivity than offshore regions, whereas during anomalous upwelling conditions of 2005 (a more localized oceanographic event), marine mammals redistributed away from Monterey Bay to areas less affected by the anomaly.

KEY WORDS: Upwelling · El Niño · Density · Diversity · California Current · Distance sampling

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Cite this article as: Burrows JA, Harvey JT, Newton KM, Croll DA, Benson SR (2012) Marine mammal response to interannual variability in Monterey Bay, California. Mar Ecol Prog Ser 461:257-271.

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