Marine Mammal Biodiversity Around Oil and Gas Platforms - Challenges and Successes of Long-Term Monitoring

Monitoring, understanding, and communicating the impact of offshore oil and gas exploration and production (E&P) activities on marine mammal (MM) biodiversity can be challenging. Here, we share methods, results, and experiences accumulated during seven years of monitoring MM and underwater sound in a mature E&P activity area in the North-East Atlantic. We collected data on the distribution and behaviour of MM, their prey and changes associated with impulsive (e.g., seismic) and continuous (e.g., platform) sound generated by E&P operations. A program was created as an incentive for offshore staff to report systematically incidental MM sightings. Underwater acoustic recorders were placed around producing facilities and across a 3D seismic survey area before, during and after acquisition. A 2nd Generation Environmental Sample Processor (ESP) was deployed to collect and analyse environmental DNA (eDNA) from seawater to identify MM species and their potential prey. Monitoring data were shared with relevant stakeholders through publications in scientific journals, presentations at conferences and meetings, or through social media. Our data provided evidence of MM activity in the E&P activity area year-round. A total of eight species were sighted from platforms and vessels; harbour porpoise being the most common MM. Harbour porpoises were recorded as being within 800m of the platform three times more often than at stations further away. Near installations, acoustic data showed porpoises actively searched for prey whilst eDNA confirmed the presence of prey species - validating a strong reef-effect. Decrease in porpoise echolocation to 8-12 km from an active seismic vessel, is suggestive of a temporary displacement of animals in the corresponding area. There was no large scale or long-term displacement as harbour porpoises were detected again in the area few hours after airgun operations ended. The results indicate that despite elevated sound level in the E&P area, porpoise distribution appears to be linked to higher availability of prey around the artificial reef created by subsea O&G structures. The monitoring efforts generate valuable scientific knowledge, which form a sound basis to support management and regulation of E&P activities in Denmark. Additionally, several simultaneous tangible benefits resulted from the study such as staff awareness of biodiversity and increased stakeholder interactions. Results and methodologies may be used by HSE practitioners and O&G project managers to assess the potential impact of sound generated by O&G industry on marine mammals. Our success illustrates the value of long-term monitoring and should inspire and support HSE practitioners in their future environmental monitoring initiatives.