Assessment of the benthic environment following offshore placer gold mining in the northeastern Bering Sea

Abstract

The effects of offshore placer gold mining on benthic invertebrates were assessed on ‘sand’ and ‘cobble’ substrates in Norton Sound, northeastern Bering Sea. Mining with a bucket-line dredge occurred nearshore in 9–20 m during June to November 1986–90. Sampling nearly a year subsequent to mining demonstrated minor alteration of substrate granulometry with no clear trends. However, benthic macrofaunal community parameters (total abundance, biomass, diversity) and abundance of dominant families were significantly reduced at mined stations. Many of the dominant taxa are known prey of the locally important red king crab ( Paralithodes camtschaticus). Dominance of opportunistic species and small sizes at unmined and mined sites represents faunal responses to the natural dynamics of the region where establishment of populations of large, sexually-mature individuals is typically precluded. Multi-year bathymetric surveys of an area only mined in 1986 showed a continued smoothing of ocean bottom relief, decreasing size of tailing footprint, and shoaling of depressions left by mining. An ordination (multidimensional scaling) of taxon abundance data from mined (1 year after mining), recolonizing (2–7 years after mining) and unmined stations shows configurations that reflect disturbance. Recovery of the biota was underway in both substrates after 4 years, but this process was interrupted in the fall of the fourth year (1990) by several severe storms. Mining effects are contrasted with local natural disturbances.