Tidal energy is a renewable resource that can contribute towards meeting growing energy demands, but uncertainties remain about environmental impacts of device installation and operation. Environmental monitoring programs are used to detect and evaluate impacts caused by anthropogenic disturbances and are a mandatory requirement of project operating licenses in the United States. In the United Kingdom, consent conditions require monitoring of any adverse impacts on species of concern. While tidal turbine sites share similar physical characteristics (e.g. strong tidal flows), similarities in their biological characteristics have not been examined. To characterize the generality of biological attributes at tidal energy sites, metrics derived from acoustic backscatter describing temporal and spatial distributions of fish and macrozooplankton at Admiralty Inlet, Washington State and the Fall of Warness, Scotland were compared using t-tests, F-tests, linear regressions, spectral analysis, and extreme value analysis (EVA). EVA was used to characterize metric values that are rare but potentially associated with biological impacts, defined as relevant change as a consequence of human activity. Pelagic nekton densities were similar at both sites, as evidenced by no statistically significant difference in densities, and similar daily density patterns of pelagic nekton between sites. Biological characteristics were similar, suggesting that generic biological monitoring programs could be implemented at these two sites, which would streamline permitting, facilitate site comparison, and enable environmental impact detection associated with tidal energy deployment.