Quantifying fish behaviour and commercial catch rates in relation to a marine seismic survey

The impact of seismic surveys on the catchability of marine fish is a contentious issue, with claims that seismic surveys may negatively affect catch rates. However little empirical evidence exists to quantify the impacts or determine potential causes. In this study, we used a 2-D seismic survey in the Gippsland Basin, Bass Strait, Australia in April 2015 as an opportunity to quantify fish behaviour (field-based) and commercial fisheries catch (desktop study) across the region before and after airgun operations. Three species found in abundance (gummy shark, swell shark, tiger flathead) were acoustically tagged and released within one of two acoustic arrays (experimental and control zone) and monitored before, during and after the seismic survey. In the field study, only 35% of the gummy sharks and 30% of the swell sharks were subsequently detected two days after release, although various individuals returned sporadically over the period of monitoring including during the seismic survey operations. Behaviour consistent with a possible response to the seismic survey operations was restricted to flathead which increased their swimming speed during the seismic survey period and changed their diel movement patterns after the survey. We also investigated the potential impacts of the seismic survey on catch rates using Commonwealth fisheries logbook data from Jan 2012 – Oct 2015. Fifteen species and two gear types (Danish seine, gillnet) were modelled to examine differences in catch rates before and after the seismic survey. The catch rates in the six months following the seismic survey were different than predicted in nine out of the 15 species examined, with six species (tiger flathead, goatfish, elephantfish, boarfish, broadnose shark and school shark) showing increases in catch following to the seismic survey, and three species (gummy shark, red gurnard, sawshark) showing reductions. Overall, we found little evidence consistent with behavioural or catch rate changes induced by the seismic survey in the targeted species, although behavioural data were limited because many sharks left the acoustic receiver array prior to the commencement of the seismic survey. Citation: Barry Bruce, Russ Bradford, Scott Foster, Kate Lee, Matt Lansdell, Scott Cooper, Rachel Przeslawski, Quantifying fish behaviour and commercial catch rates in relation to a marine seismic survey, Marine Environmental Research, Volume 140, 2018, Pages 18-30, ISSN 0141-1136. https://doi.org/10.1016/j.marenvres.2018.05.005.