Examining Fisheries Catches and Catch Rates for Potential Effects of Bass Strait Seismic Surveys

Brief description

Marine seismic surveys are used to identify geological structures of the seafloor that may be indicative of oil and gas deposits, and they represent a major source of anthropogenic underwater noise. This desktop study was initiated in response to concerns raised by the fishing industry during stakeholder consultation prior to a proposed seismic survey in the Gippsland Basin, Australia. This study therefore aims to investigate whether a statistical relationship exists between marine seismic operations and reduced fish catch rates in the Bass Strait and Gippsland Basin, with possible causative relationships identified by declines in catch-per-unit of effort (CPUE) that consistently occur in association with seismic operations. In order to account for other factors influencing CPUE, we also investigate potential relationships between several environmental variables and historical fish catch rate for key commercial species in the Bass Strait region.

The analyses used here range from simple mean comparisons of catch rates before and after seismic surveys to the development of novel measures of the potential links between the spatial and temporal location of each seismic survey and the array of available catch and effort data from individual fishing records. Three novel generalized linear models were used that employed natural splines to allow flexibility in the nature of the estimated relationships between catch rates (or catches) and potentially influential factors: Method 1 (All surveys) in which all seismic surveys were considered as independent variables, Method 2 (Nearest neighbour) in which the effect of just one survey (the 'nearest' in space and time) was considered for each fishing operation, and Method 3 (Cumulative impacts) in which the sum of variables across seismic surveys estimated cumulative impacts of all seismic surveys.

None of the analyses conducted on these data identified any clear or consistent relationship between seismic surveys and subsequent fisheries catch rates. This does not imply that such impacts do not exist, merely that the data available to this study did not permit an unequivocal outcome. In terms of duration since a seismic survey, significant effects, both positive and negative, were found but could not be distinguished from ecological interannual effects brought about by stock size changes resulting from other dynamics. Environmental factors were included in analyses for four species (gummy shark, tiger flathead, school whiting, silver warehou), and they showed significant effects upon commercial catch rates; however their influence on the apparent seismic effects (which are confounded with year effects) was very minor to insignificant. It has become clear that a desktop study using fisheries catch and effort data from commercial logbooks compared to relatively gross scale seismic data does not provide a simple solution to the question of potential negative impacts.

This study revealed several challenges with data availability and quality. Despite failing to find a consistent, significant negative (or positive) effect of seismic surveys on catch rates, the analyses in this report present some novel approaches to solving this problem. Suggestions are made for further methodological improvements.

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