An Assessment of Potential Mining Impacts on Salmon Ecosystems of Bristol Bay, Alaska

Millions of Pacific salmon return from feeding in the open ocean each year and swarm through Bristol Bay en route to their natal spawning streams. Nine major river systems comprise the spawning grounds for Bristol Bay salmon (Figure 1), and schools navigate toward the mouths of their respective rivers as they pass through the Bay. Each summer, thousands of commercial fishermen use drift and set gill nets to capture millions of returning fish, making Bristol Bay the largest sockeye salmon fishery in the world. Salmon that escape the fishery distribute throughout the Bay's watersheds and spawn in hundreds of discreet populations. Sport anglers target those salmon, especially sockeye, Chinook and coho, as they migrate through the river systems toward their spawning grounds. Also prized are abundant populations of rainbow trout and other sport fish, including Dolly Varden and Arctic grayling, which attain trophy size by gorging on energy-rich salmon eggs, flesh from salmon carcasses, and invertebrates dislodged by spawning salmon. The abundance of large game fish, along with the wilderness setting, makes the Bristol Bay region a world-class destination for sport anglers. Alongside recreationists, aboriginal people, guided by an age-old culture, harvest their share of migrating salmon and other fish species, which provide a primary source of sustenance. In this report we reviewed the biology, ecology, and management of the fishes of the Bristol Bay watersheds, emphasizing those species of the greatest cultural and economic importance - sockeye salmon, Chinook salmon, and rainbow trout. Rather than to imply that other fishes are not important, this focus reflected the disproportionate amount of research on these species (especially sockeye salmon) and was necessary to keep the amount of material manageable. In contrast, there is relatively little information available for the region's freshwater species, despite the importance of some in subsistence and sport fisheries. Our objectives were to describe the commercial and sport fishery resources of the region and to discuss the importance of Bristol Bay salmon populations in the context of the greater North Pacific Ocean. The literature reviewed consisted primarily of agency reports and peer-reviewed scientific papers, although unpublished data and personal communications were used where no pertinent published literature existed and popular sources were consulted to characterize the more subjective attributes of the sport fisheries. Our geographic focus was the Kvichak River watershed (including the Alagnak River) and the Nushagak River watershed (including the Wood River). Since the Kvichak and Nushagak sockeye salmon populations are components of the Bristol Bay-wide stock complex, however, we typically discuss their abundance trends at both the Bristol Bay scale and at the scale of the individual river systems. The economics of Bristol Bay's fisheries and the role of fish in the region's aboriginal cultures are each covered in separate sections of the Bristol Bay Watershed Analysis.