Skip to main content
U.S. flag

An official website of the United States government

Changes in fish diets and food web mercury bioaccumulation induced by an invasive planktivorous fish

December 1, 2008

The invasion, boom, collapse, and reestablishment of a population of the planktivorous threadfin shad in Clear Lake, California, USA, were documented over a 20-year period, as were the effects of changing shad populations on diet and mercury (Hg) bioaccumulation in nearshore fishes. Threadfin shad competitively displaced other planktivorous fish in the lake, such as inland silversides, young-of-year (YOY) largemouth bass, and YOY bluegill, by reducing zooplankton abundance. As a result, all three species shifted from a diet that was dominated by zooplankton to one that was almost entirely zoobenthos. Stable carbon isotopes corroborated this pattern with each species becoming enriched in δ13C, which is elevated in benthic vs. pelagic organisms. Concomitant with these changes, Hg concentrations increased by ∼50% in all three species. In contrast, obligate benthivores such as prickly sculpin showed no relationship between diet or δ13C and the presence of threadfin shad, suggesting that effects of the shad were not strongly linked to the benthic fish community. There were also no changes in Hg concentrations of prickly sculpin. The temporary extirpation of threadfin shad from the lake resulted in zooplankton densities, foraging patterns, isotope ratios, and Hg concentrations in pelagic fishes returning to pre-shad values. These results indicate that even transient perturbations of the structure of freshwater food webs can result in significant alterations in the bioaccumulation of Hg and that food webs in lakes can be highly resilient.

Citation Information

Publication Year 2008
Title Changes in fish diets and food web mercury bioaccumulation induced by an invasive planktivorous fish
DOI 10.1890/06-1415.1
Authors Collin A. Eagles-Smith, Thomas H. Suchanek, Arthur E. Colwell, Norman L. Anderson, Peter B. Moyle
Publication Type Article
Publication Subtype Journal Article
Series Title Ecological Applications
Series Number
Index ID 70179560
Record Source USGS Publications Warehouse
USGS Organization Western Ecological Research Center