Stratification, sulfide, worms, and decline of the Eared Grebe (Podiceps nigricollis) at the Salton Sea, California

• Published in: Lake and reservoir management Vol. 23; no. 5; pp. 500 - 517
• Main Authors: Anderson, Thomas W., Tiffany, Mary Ann, Hurlbert, Stuart H.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.12.2007
• Subjects: Cyanobacteria; Freshwater; Gulf of California; hydrogen sulfide; Marine; migration; Neanthes succinea; Oreochromis; Oreochromis mossambicus; plankton; Podiceps nigricollis; saline lakes; starvation; stratification; tilapia; trophic cascade; Urolepis hornorum; ISE, Mexico, California Gulf; USA, California, Salton Sea
• ISSN: 1040-2381; 2151-5530
• DOI: 10.1080/07438140709354034

Over the last half century the Salton Sea has been an important migratory stopover site for the Eared Grebe (Podiceps nigricollis). However, in recent years there have been sporadic mass mortalities (i.e., 150,000 in 1992) and a great reduction in the number of grebes visiting during the winter. We propose that a worsening food supply is causing the decline and that starvation may be a major cause of the unexplained mortalities. While at the Sea, grebes forage almost exclusively on a benthic polychaete, the pileworm (Neanthes succinea). This resident pileworm population has increasingly been subject to periodic crashes driven by exposure to anoxic, sulfide rich, hypolimnetic water following lake mixing events. A set of interlocking mechanisms seem to be operating. These involve, in particular, increasing lake salinity, weather events favoring lake stratification, and booms and busts in tilapia (Oreochromis mossambicus × O. urolepis hornorum) and plankton populations, including those of toxic cyanobacteria. In spring, Eared Grebes arrive from the Gulf of California and many arrive in need of food to fuel the remainder of their migration. When pileworms are scarce, many grebes are able to continue on toward their northern breeding grounds, but those that lack sufficient energy stores are forced to stay and may eventually perish. This analysis is surely incomplete, and definitive explanations of the excessive drinking and waterlogged plumage often exhibited by Eared Grebes during mass dieoffs have yet to be found.