Do seismic surveys kill zooplankton?

Funding agency: The Institute of Marine Research, North Sea Program.
Project period: 2019-2020
Project leader: Lise Doksæter Sivle
Co-investigators: Karen de Jong, Nils Olav Handegard, Egil Ona, Howard Browman, Anne Berit Skiftesvik+++
Project summary
The effects of seismic sound on ocean life are not necessarily limited to larger taxa. Small animals could be exposed to shaking from sound waves, which could potentially damage and even kill individuals. The smallest animals in the world’s oceans, zooplankton, are crucial ocean productivity and the survival of larval fish. McCauley et al. (2018) report zooplankton mortality up to 1200 m from a seismic transect, and infer a causal relationship. If true, these data would mean that seismic explorations could kill zooplankton on long distances around an airgun, and thus affect productivity in large areas. However, the set-up used in the paper does not allow for testing whether mortality could have been caused by other sources of disturbance, such as the propeller wake of the ships used the experiment or variation in natural mortality over the day. An experimental study by Fields et al. (in press) found mortality only within a 5m range from the source using caged individuals at several distances from an airgun. IMR is responsible to give advice to all seismic operations in Norwegian waters. If the results presented by McCauley et al. are correct, seismic operations in areas with high zooplankton concentrations should be discouraged. To evaluate whether such dramatic advices should be given, we need to assess and understand the potential effects on population. We therefore propose a step wise combination of lab and field studies. Lab studies will give insight in the processes of how zooplankton can potentially be affected and can demonstrate whether propeller wash could be an alternative explanation for the mortality found in McCauley et al. instead of the seismic itself. Fields studies on the other hand are needed to understand large scale effects in a natural environment, and potential avoidance behaviours, caused by a real air-gun, field studies are necessary.