CGG has NOPSEMA approval for a 3D seismic survey in the Gippsland Basin to commence in early 2020. This survey overlaps the Victorian shelter-pot octopus fishery off Lakes Entrance. This overlap has raised concerns from the fishing industry about the potential impacts to octopus and the fishers. Tank-based experiments simulating seismic exposure have resulted in high levels of damage in several species of octopus, however, it is unclear how experiments conducted in tanks translate into the field. Field-based seismic experiments have rarely been conducted on invertebrates, with no such studies conducted on octopus. However, the benthic and relatively sessile habit of octopus leaves them potentially vulnerable to impacts, as they have limited capacity to avoid the waterborne and ground-borne energy of seismic signals. CCG has agreed to provide funds to fill the knowledge gap surrounding the potential impact of seismic surveying on octopus and to do this in conjunction with a commercial scale seismic survey, with the lack of a full array often a perceived limitation of seismic research. CGG has also agreed to value add to the work around octopus. This opportunity allows for the potential impact of seismic surveying on larval forms to be examined, with some concerns around localised depletion of larvae of commercially and ecologically important species, such as southern rock lobster and commercial scallops. This project will use a field and laboratory experimental approach to provide a thorough assessment of the potential impacts of seismic surveys on octopus pallidus and its catches, along with rock lobster larvae and other important larvae. These approaches may assist fisheries and petroleum regulators to make informed decisions on the timing and manner in which future surveys are performed. Importantly, along with that of CGG, it has the support of the Victorian Fisheries Authority, who have also offered in-kind support, the two octopus fishers in the region, the Lakes Entrance Fishermen’s co-op, the sustainable shark fishing association and Southern Rock Lobster Inc.
Report
Key Findings
Exposure did not result in any elevated mortality for puerulus or juveniles. Immediately after exposure, righting was significantly impaired for all exposure treatments (E0 and E500 for juveniles and E0 for puerulus) compared to their respective controls, indicating that the impact range extended to at least 500 m from the source, the maximum range tested in the present study. After the first moult, there was no significant difference found in righting between juvenile Control and E0 treatments, and for puerulus, small sample size precluded statistical analysis. When these two stages were pooled, the combined E0 treatment was found to be significantly impaired. In the juvenile E500 lobsters, righting was similar to that of Controls, indicating that the lobsters had recovered from prior impairment. After the second moult, juvenile E0 lobsters showed significant impairment compared to controls. When puerulus, which could not be analysed due to small sample size, were pooled with juveniles, the combined E0 treatment was significantly impaired relative to combined Controls. Righting in juvenile E500 lobsters was similar to that of controls, further supporting recovery in this treatment. Impaired righting has previously been found to correlate with damage to the statocyst, the mechanosensory organ common to many marine invertebrates. The results here from the combined puerulus and juvenile treatments indicated that puerulus and juvenile E0 treatments did not show the capacity for recovery whereas juvenile E500 lobsters recovered from impairment after the first moult, providing evidence of a range threshold for recovery. Intermoult period was significantly increased in E0 juvenile lobsters and appeared to be increased in puerulus, though the latter could not be statistically analysed. Juvenile E500 treatment showed a moderate, non-significant increase in moult duration. Increased intermoult duration suggested impacted development and potentially slowed growth, though the proximate cause was not identified.
• Sound exposure levels recorded in this study were similar to those of prior experiments conducted with a single air gun, validating the single air gun approach for future field-based experimental work.
• Air gun signals caused righting impairment to at least 500 m, the maximum range in this study, in lobsters sampled immediately following exposure, a similar result previously reported in adults that corresponded with significant damage to the mechanosensory statocyst organ that provides the sense of balance, body position and movement that are critical for predator avoidance behaviour.
• Impairment resulting from close range exposure (i.e., combined puerulus and juvenile E0 treatments) appeared to be persistent, as previously reported in adult lobsters, whereas lobsters exposed at a more distant range (juvenile E500) showed recovery. This indicates that a range of 500 m may not cause lasting impairment to righting.
• Intermoult duration was significantly increased in E0 juveniles and appeared to be increased in E0 puerulus, indicating the potential for slowed development and growth and physiological stress.
