Field Assessment of Colorado pikeminnow Exposure to Mercury Within Its Designated Critical Habitat in Colorado, Utah, and New Mexico

Abstract

Mercury contamination in freshwater fish is widespread across North America, including the western United States. Atmospheric mercury from both natural and manmade emissions deposits into watersheds and, through methylation and biomagnification, accumulates in aquatic food webs. Highest mercury concentrations are found in predatory fish. The endangered Colorado pikeminnow (Ptychocheilus lucius) is a long-lived, top-level piscivore endemic to the Colorado River basin. Mercury exposure to Colorado pikeminnow and another native fish species, the roundtail chub (Gila robusta), was assessed by analyzing muscle tissues collected using a nonlethal technique. Mercury concentrations in Colorado pikeminnow > 400-mm long, captured from critical habitat throughout the species’ present range, exceeded the tissue threshold-effect level of 0.2 µg/g wet weight (WW) for whole body fish (0.31 µg/g WW in muscle) recommended to protect fish from injury. Mercury is a neurotoxin and endocrine disruptor, and impacts to fish may include reduced ability to avoid predators, secure food, and reproduce. The highest mercury concentrations were found in both Colorado pikeminnow and roundtail chub collected from the White River, a tributary to the Green River. Colorado pikeminnow from the White and Green rivers had the highest mean mercury concentrations and the lowest mean relative body conditions. Exposure to high mercury concentrations may act in concert with other threatening factors to compromise Colorado pikeminnow population viability and eventual recovery.

Mercury and selenium concentrations in fishes of the Upper Colorado River Basin, southwestern United States: A retrospective assessment

“…Eagles-Smith et al [9] describes the details on data quality, data validation, assumptions, and standardization from these Federal and State data sources. We augmented these 1,861 individual fish records with another 463 records from several sources not included in the original database [31][32][33][34]. The cumulative dataset spans from 1962 to 2011 and includes 2,324 individual fish records (1,355 with both THg and Se concentrations, 604 with only THg concentrations, and 365 with only Se concentrations) from 33 species of fish [35].…”

“…Thus, in the San Juan, fish Hg concentrations may not reflect the true risks to this populations. See Osmundson and Lusk [76] for a more thorough assessment of Hg risks to Colorado Pikeminnow and Roundtail Chub.…”

Temporal Influences on Selenium Partitioning, Trophic Transfer, and Exposure in a Major U.S. River

“…Fishes were collected by seine, D-nets, and electrofishing and measured for total lengths. Speckled Dace and small Roundtail Chub were collected whole, and 3 mm muscle biopsies were taken from fish greater than 200 mm in length using previously described methods . Our fish collections were supplemented by FWS samples collected during coinciding sampling trips in August and October 2015 and 2016 and assigned to the nearest focus site using recorded sampling location coordinates.…”