Mercury Residues and Productivity in Osprey and Grebes From a Mine‐dominated Ecosystem

Abstract

Grebe productivity at Clear Lake improved from ;0.1 to 0.5 fledged young per adult during the latter part of the study when human disturbance was prevented. At that period in time, improved productivity did not differ from our reference site at Eagle Lake. Human disturbance, however, as a co-factor made it impossible to evaluate statistically subtle Hg effects on grebe productivity at Clear Lake. Osprey reproduced sufficiently to maintain increasing breeding numbers from 1992 to 2006. Mercury in Clear Lake water, sediments, invertebrates, and fish did not decline from 1992 to 2003, but a shift in trophic structure induced by an introduced planktivorous fish species may have caused significant alterations in Hg concentrations in several species of prey fishes that may have produced concomitant changes in Osprey and grebe Hg exposure. The temporary declines observed in grebe and Osprey feather residues in the late 1990s, with coincidental improvements in reproductive performance, however, could not be attributed to remediation at the mine site.

Spatiotemporal Trends in Fish Mercury From a Mine‐dominated Ecosystem: Clear Lake, California

“…This conclusion resulted from both a refinement of the original methodology and site-specific data on fish tissue concentration relationships between trophic levels. In addition to these findings, MeHg concentrations that would be protective of Osprey, a common piscivorous bird species nesting and reproducing at Clear Lake (see Anderson et al 2008), were calculated at 0.10 mg/kg and 0.17 mg/kg for trophic level 3 and trophic level 4 fish, respectively. Based on these calculations, nearly all of the largemouth bass and channel catfish at Clear Lake would exceed tissue Hg concentrations that would be protective of Bald Eagles and Osprey (see Fig.…”

Mercury Trophic Transfer in a Eutrophic Lake: The Importance of Habitat‐specific Foraging

“…This study provides the linkage between MeHg entry at the base of the food web, through accumulation in higher trophic level fishes and piscivorous birds (Anderson et al 2008). It also provides a foundation for understanding the relative importance of both foraging habitat and trophic position in the transfer of Hg through successive trophic levels.…”

Wintering ecology of sympatric subspecies of Sandhill Crane: Correlations between body size, site fidelity, and movement patterns

“…In 1992, Hg residues in grebes at Clear Lake were elevated relative to those at two comparison sites in northeastern California (Eagle Lake and Tule Lake) and were approaching approximate threshold levels for reproductive effects in birds. Still, there were no discernible population-level effects of Hg measured in adult grebes during intensive studies from 1992 to 2001 (and at least through 2006;Anderson et al 2008). Improved nesting success of grebes was not attributable to mine site remediation and declining Hg residues (exposure) but rather to protection of colonies from major disturbance events.…”