Fish Presence and Water Quality in a Proposed Copper Mining District, Alaska

Bristol Bay supports the largest, most valuable salmon fisheries in the US, and is the last major watershed in North America producing historic numbers of wild sockeye salmon.  However, industrial mining interests have claimed 2,054 km² in these habitats, threatening two of Bristol Bay’s largest salmon producing drainages, the Kvichak and Nushagak.  If proposed sulfide mining occurs, the preponderance of peer-reviewed evidence indicates significant risks to fisheries due to metals contamination, habitat degradation and habitat loss.

Since 2008, independent scientists have been conducting water chemistry, habitat, and fish surveys in headwaters of the proposed mining area. Data indicate salmon presence in 3 of every 4 headwater streams surveyed.  Non-salmon species important to subsistence and sportfishing stakeholders, including Dolly Varden and rainbow trout, were found in 93% of streams surveyed.  Waters supporting these fish populations are important due to their purity and the exchange between ground- and surface waters.  Although salmon preferentially use groundwater-fed sites for spawning, actual groundwater locations remain unmapped; here, we tentatively identify groundwater influence based on water chemistry.  Stream waters are pure, with high dissolved oxygen, very low conductivity and metals concentrations, and neutral pH.  Low alkalinity indicates little buffering capacity, while low dissolved organic carbon suggests metals released due to landscape disturbance from mining would remain bioavailable, degrading stream chemistry for fish.

This study underscores both the importance of headwater streams as essential salmon rearing habitat and the lack of data for two of the world’s most productive salmon ecosystems.  The fish survey work provides some legal protections to 149 km of newly documented salmon streams in and near proposed mine claims.  Water quality studies suggest waters are pure with low buffering capacity and therefore susceptible to potential acid mine drainage and increased metals from sulfide ore mining.  Future analysis will integrate physical and biological data in order to evaluate baseline biodiversity and productivity in this important region.