Thysanoessa spinifera is an important prey item in the diet of Cassin's Auklet (Ptychoramphus aleuticus) in the Gulf of Farallones, California, USA. Ainley et al. (1996) report that once seasonal upwelling makes T. spinifera available, P. aleuticus relies heavily on this relatively large and energetically valuable euphausiid. They also report a Cassin's Auklet population decline of about 50% coincident with a general decline of zooplankton in the California Current. In general, long term studies through the 1970s and 1980s indicate that variations in upwelling activity have a strong impact on the availability of euphasiids, which in turn strongly impacts Cassin's Auklet populatons (Ainley et al. 1996). Abraham and Sydeman (2006) note that both long-term and short-term changes in prey availability are reflected in the diets of Cassin's Auklets, providing support for the idea that monitoring the diets and reproductive success of top marine predators can be used as an additional tool to monitor the distribution and abundance of forage fishes and zooplankton.
In a study of the feeding habits of the world's largest stock of blue whales (Balaenoptera musculus), near the Channel Islands off southern California, in the summers of 1995 and 1996, the krill species Thysanoessa spinifera and Euphasia pacifica were found to be a major component of the diet of blue whales, with a preference shown for the larger, more coastal E. spinifera (Fiedler et al. 1998). These same two krill species were found to dominate the diets of blue whales foraging in Monterey Bay (central coast of California, USA) (Croll et al. 2005). A blue whale may consume up to two tons of krill each day (Rice 1978, cited in Fiedler et al. 1998).
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