Contemporary and Future Landscape-Based Anthropogenic Disturbances to Alaska Streams: Implications for Anadromous Fish Habitat Conservation
Arthur R. Cooper, Dana M. Infante, Jared A. Ross, Wesley M. Daniel, Kyle Herreman, Christopher C. Estes, and Gary E. Whelan
Abstract.—Fluvial threat assessments characterize the potential for fluvial habitat conditions to be degraded by differing types and intensities of anthropogenic activities occurring on the landscape, ultimately affecting stream biota. We present a threat assessment for fluvial habitats in Alaska based on six anthropogenic disturbance indices representing urbanization, agriculture/timber harvest, stream fragmentation, point-source pollution, infrastructure, and mines. These indices were combined to develop an overall index of contemporary threat of habitat alteration throughout Alaska using the 12-digit U.S. Geological Survey hydrologic unit code (HUC-12) framework (n = 13,997) and at a finer spatial resolution using local and network catchments for individual stream reaches within Southeast Alaska (n = 207,092). Overall, contemporary threat of habitat alteration indices showed that ~96% of fluvial habitats both statewide and for Southeast Alaska were at low or very low levels; however, anadromous fish habitats were under greater human pressure with nearly double the amount of moderately to severely disturbed habitats when compared to all fluvial habitats. We further evaluated potential future threats to fluvial habitats from mineral mining activities and climate change. More than 86% of existing mine claims statewide and 99% of claims in Southeast Alaska occur in areas of low and very low contemporary threat to fluvial habitats for anadromous fishes. Under climate change, July air temperatures are projected to increase ~1.9°C, on average, by mid-century within HUC-12s containing anadromous fish streams, indicating immense potential to warm streams with anadromous fishes within the state. This fluvial threat assessment demonstrates that overall threats from contemporary anthropogenic disturbance factors are generally low with localized areas of high intensity. However, future threats from mining and climate change have considerable potential to alter fluvial habitats for anadromous fishes in Alaska, particularly those currently unaltered by anthropogenic disturbances.