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

Abstract

Anderson, T.W., M.A. Tiffany and S.H. Hurlbert. 2007. Stratification, sulfide, worms, and decline of the Eared Grebe (Podiceps nigricollis) at the Salton Sea, California. Lake Reserv. Manage. 23:500-517.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.

Length-weight relations and growth rates of dominant fishes of the Salton Sea: implications for predation by fish-eating birds

“…Proximal factors for the declines include rising salinity of the Sea, currently at 45 g L -1 (Sardella et al 2004(Sardella et al , 2007 , diseases (Friend 2002;Nol et al 2004;Rocke et al 2004), parasites and ectosymbionts (Kuperman and Matey 1999;Kuperman et al 2001Kuperman et al , 2002, episodes of cold weather, and deoxygenation and sulfide events during the warm season (Watts et al 2001;Riedel et al 2002;Caskey et al 2007). Those factors have also been associated with extensive deaths of tilapia between 1999 and 2000, and deaths of over 200,000 migratory water birds (Jehl 1996;Kaiser 1999;Caskey et al 2007;Anderson et al 2007). …”

Factors Influencing Mortality of Eared Grebes (Podiceps nigricollis) during a Mass Downing

“…In contrast, observations of Eared Grebes in fall migration indicate that the flight does not begin until after sunset (Jehl and Henry 2010). Ecological conditions at the Salton Sea are changing rapidly, which, as its level drops and salinity increases, will eventually become too salty to support worms (Anderson et al 2007; Hurlbert et al 2007). We encourage studies of stomach contents in future spring downings because they may provide insight into changes in food resources or in staging areas themselves.…”

“…At the Salton Sea, pile worms (Neanthes succinea) have been Eared Grebes' major food yet have declined in the last decade (Jehl and McKernan 2002;Anderson et al 2007). Mouthparts of pile worms typically occur in the hundreds or thousands in the gizzards of Eared Grebes at the Salton Sea (Jehl and McKernan 2002).…”

Dramatic blooms of Prymnesium sp. and Alexandrium margalefii in the Salton Sea, California

“…In 1997-1999, when the salinity measured 41-45 g l -1 , the phytoplankton community in the Salton Sea was dominated by dinoflagellates, diatoms, cryptomonads and a raphidophyte 7 . By spring of 2005, filamentous cyanobacteria had became abundant after a collapse of the tilapia fishery 8 . The salinity is now (January 2008) at or approaching 50 g l -1 .…”