Acoustic monitoring of marine seismic survey impacts on fish and zooplankton in the northeast Newfoundland slope marine refuge

Hynes, Hannah (2024) Acoustic monitoring of marine seismic survey impacts on fish and zooplankton in the northeast Newfoundland slope marine refuge. Masters thesis, Memorial University of Newfoundland.

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Abstract

I investigated the impacts of seismic surveying on fish and zooplankton in a coastal and an offshore environment. Sound levels produced by a seismic source (coastal: single vessel deployed airgun; offshore: seismic vessel) were recorded and changes in fish and zooplankton abundance, distribution, and behaviour were monitored using hydroacoustic technology up to a range of 1km in the coastal experiment and 150 km in the offshore environment. For the coastal experiment, both a mooring, deployed to a bottom depth of ~80m, and vessel mounted echosounders used active acoustic technology to collect data during the experiment. The offshore experiment used a mooring equipped with both passive and active acoustic technology deployed at a depth of ~350 m to collect data. This study provided evidence that fish at depths between 50 m and 350 m reacted to offshore seismic surveying within a 62 km horizontal radius. They descended and aggregated deeper in the water column. However, I did not observe any effect on the abundance nor behaviour of zooplankton. There were no significant measurable effects on fish or zooplankton from the single airgun coastal experiment. Mortality rates of zooplankton were also assessed using net sampling and dyeing methods in both coastal and offshore experiments, but I did not detect significant changes in zooplankton mortality. These studies were limited by minor technological issues offshore with acoustic equipment which limited the monitoring of the water column to depth between 50 and 350 meters. The number of zooplankton samples was also limited by inclement weather at the time of sampling and safety restrictions which limited approaching within 5 km of the seismic vessel. Despite these limitations, my findings suggest that the effects of seismic surveying in an offshore subarctic environment are impacting vertical fish distribution but not causing detrimental effects on zooplankton abundance and mortality.

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