Investigating biophysical linkages at tidal energy candidate sites: a case study for combining environmental assessment and resource characterisation

As the tidal energy industry looks to expand into commercial-scale array installations, uncertainty in methodology and outcome for environmental impact assessments can encumber tidal energy developments. Incorporating environmental monitoring measures into site characterisation campaigns can provide baseline information about biophysical relationships and help recognise potential impacts to the marine environment early in the development process. Concurrent measurements of fish and tidal currents were taken at a tidal energy candidate site in Australia over ∼2.5 months during its tidal resource assessment. Fish aggregation metrics (density, abundance, centre-of-mass (CM), dispersion, %-water column occupied, evenness, and relative aggregation) were investigated for their relation to environmental conditions (current speed, shear, temperature, diel stage, and tidal stage). Diel stage was the most significant indicator for fish density, abundance, and %-water column occupied. Fish density and abundance were elevated during strong currents, with vertical fish distribution (CM and dispersion) also influenced by current speed. Environmental conditions were able to explain up to 25% of variation in fish aggregation metrics using linear models. This study shows that early-stage environmental monitoring can successfully provide baseline information about fish aggregation responses to prevailing environmental conditions, thus reducing uncertainty risks for stakeholders of tidal energy developments.