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From Wind to Whales: Trophic Links in a Coastal Upwelling System

Croll, D.A., B. Marinovic, S. Benson, F.P. Chavez, N. Black, R. Ternullo, and B.R. Tershy (2000)

Final Report to the Monterey Bay National Marine Sanctuary, Contract No. 50ABNF500153.

ABSTRACT

Due to their large body size and high mammalian metabolic rate, blue whales (Balaenoptera musculus) have the highest average daily total energy requirement of any species. Blue whales meet this energy demand by feeding exclusively upon dense but patchy schools of euphausiids. We used an integrated approach to determine whether a unique combination of seasonally high primary production supported by coastal upwelling works in concert with topographic breaks in the continental shelf off California to collect and maintain large concentrations of euphausiids that are exploited by foraging whales. Specifically we used concurrent ship- and mooring-based oceanographic, hydroacoustic, and net sampling, opportunistic whale sighting records, systematic visual surveys, and time-depth recorder deployment to: 1) define prey patches and whale foraging behavior within patches, 2) determine spatial and temporal patterns in the distribution and abundance of whale prey patches, and 3) examine the biotic and abiotic factors important in creating whale foraging patches in the seasonal upwelling context of Monterey Bay, California between 1992-1996.

Blue whales fed exclusively upon epipelagic euphausiids (Thysanoessa spinifera and Euphausia pacifica) that were larger and in proportions from that generally available in the Bay. Foraging blue whales targeted schools of adult T. spinifera, diving repeatedly to extremely dense patches aggregated between 150 and 200m on the edge of the Monterey Bay Submarine Canyon. These patches averaged 145 g m-3, approximately two orders of magnitude greater than the densities generally available in the Bay (1.3 g m-3). High euphausiid densities are supported by a combination of high primary production between April and August (average peak production 249 mg-C m-3 day-1) and the presence of a deep canyon that provided deep water downstream from the Davenport/Año Nuevo coastal upwelling center. Peak euphausiid densities occur in late summer/early fall, lagging the seasonal increase in primary production by 3-4 months. This lag likely results from both the temporal development of euphausiids spawned around the seasonal increase in primary production in the spring and the shoreward collapse of productivity due to decreased intensity of coastal upwelling in the late summer. The annual migratory movements of the California blue whale likely reflect seasonal patterns in productivity in other foraging areas similar to those we have described for Monterey Bay.

Suggested Citation:

Croll, D.A., B. Marinovic, S. Benson, F.P. Chavez, N. Black, R. Ternullo, and B.R. Tershy. 2000. From Wind to Whales: Trophic Links in a Coastal Upwelling System. Final Report to the Monterey Bay National Marine Sanctuary, Contract No. 50ABNF500153.

URL: http://montereybay.noaa.gov/research/techreports/trcroll2000.html    Reviewed: March 04, 2014
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