Using extirpation to evaluate ionic tolerance of freshwater fish.

Area of Science:

• Environmental Toxicology
• Ecology
• Aquatic Science

Background:

• Elevated ion concentrations in freshwater ecosystems pose a threat to aquatic life.
• Assessing species tolerance to environmental stressors is crucial for conservation efforts.

Purpose of the Study:

• To estimate the tolerance of freshwater fish to elevated ion concentrations.
• To compare the predictive accuracy of species-level versus genus-level analyses for fish extirpation thresholds.

Main Methods:

• Utilized field data on fish occurrences and specific conductivity.
• Derived extirpation concentrations at the 95th percentile (XC95) using a weighted cumulative frequency distribution.
• Customized methods previously applied to macroinvertebrate genera for fish analysis.

Main Results:

• Genus-level extirpation concentrations (XC95) were generally close to those of the most salt-tolerant species within the genus.
• Species-level analysis is not reliably predicted by genus-level thresholds, except for monospecific genera.
• 5% of 101 fish species had XC95 values below 509 µS/cm; 10% were below 565 µS/cm.
• Above 509 µS/cm, 41 fish species are expected to decline.

Conclusions:

• Genus-level assessments may underestimate the impact of elevated ion concentrations on fish communities.
• Species-specific tolerance data are essential for accurate risk assessment and management of freshwater ecosystems.
• The study provides critical data for understanding fish sensitivity to salinity in Appalachian streams.