PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 141, Summer 2005: Notes and Discoveries from the Field

What does the virtual absence of krill this year portend for marine wildlife?




  

Cassin's Auklets Abandon Farallon Nest Colonies

Russ Bradley


 
Executive Director's Column
Return of the Least Bell's Vireo
Mystery Oil Spill
Bird Bio
Eastern Sierra
Seabirds at Vandenberg
Farallon Auklet News Flash
 


This May, PRBO scientists on Southeast Farallon Island witnessed a mass abandonment of nests by Cassin's Auklets, unprecedented in our 35 years of Farallon seabird monitoring in cooperation with U.S. Fish and Wildlife Service.

The Cassin's Auklet, a small sturdy relative of puffins and murres, is a plankton-eater that dives for its krill prey. In previous years of low ocean productivity, auklets have bred in lower numbers and later in the season, but 2005 was unique.

This year, Farallon auklets began breeding very late in April, and most abandoned their eggs during May. A small pulse of breeding began in late June, but 2005 is shaping up to be the worst reproductive year for Cassin's Auklets in our records.

Food web productivity and krill abundance depend on seasonal upwelling of cold, nutrient-rich water, which has been weak and intermittent this year. There have been other signs of scarcity, as well:

* Pelagic Cormorants, one of the first Farallon species to modify or cease nest efforts in lean food years, never even made earnest attempts to breed.

* In oceanographic research (Observer 140), PRBO found very sparse concentrations of marine wildlife near the Farallon Archipelago in May and June.

* In May, PRBO biologists analyzed king salmon stomachs, provided to us by regional fishers. Most of the 120 samples were empty; none contained juvenile rockfish; and only one contained krill.

* Moss Landing Marine Lab found a significant increase in mortality of auklets, cormorants, and Common Murres--almost all apparently due to starvation--from beach watch surveys in Central California from January to May.

* Trawl surveys conducted by NOAA Fisheries off the Central Coast found near-record lows of young-of-the-year groundfish (including rockfish), squid and krill.

What do these phenomena signify? Is the 2005 nest desertion by Cassin's Auklets part of a natural cycle newly registered in PRBO's long-term research? Or are we witnessing evidence of a warming trend in the Earth's ocean-climate? What does the virtual absence of krill this year portend for marine wildlife that relies on normally abundant food resources off the Central California coast?

PRBO will seek answers in our ongoing studies of seabirds--real-time indicators of change in the marine ecosystem.

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