Demonstrating an acceptable level of impact: an assessment of noise impacts to fishes from a seismic survey in an Australian Marine Park

Abstract

A key challenge of the environmental regulatory framework for offshore petroleum activities in Australia is the requirement to demonstrate acceptability, with the legislation placing the onus on petroleum titleholders to demonstrate that the impacts and risks posed by an activity will be of an acceptable level and reduced to as low as reasonably practicable. This paper presents a case study on the assessment of noise impacts to fishes for the Bethany 3D Marine Seismic Survey, which was acquired by Santos Ltd in mid-2018. The survey area was encompassed entirely by the Oceanic Shoals Marine Park, and also overlapped a significant proportion of the Timor Reef Fishery, a regionally important demersal scalefish fishery. The survey area overlapped a key ecological feature and a range of geomorphic features characterised by benthic habitats supporting demersal and benthic fish communities, including site-attached species. On this basis, the evaluation of impacts and risks required a multi-faceted approach, with seven key elements: (1) acoustic modelling; (2) application of sound exposure guidelines; (3) a quantitative risk assessment (benthic habitat predictive modelling and spatial analysis of site-attached fish assemblages); (4) the definition of an acceptable level of impact; (5) a sound source verification process; (6) engagement with key stakeholders; and (7) an independent, expert peer review process. The outcomes of each of these steps were incorporated into the environment plan, and enabled the titleholder to demonstrate that, with adopted control measures in place, environmental impacts and risks from the seismic survey could be managed to an acceptable level.