Decommissioning is a growing industry in the North Sea. Exploration and Production to satisfy global demand has resulted in the ongoing operation of thousands of offshore structures and the continued establishment of new infrastructure in the marine environment (e.g. Todd et al., 2020d). Of these, 7,500 marine offshore O&G installations across jurisdictions of 53 countries are expected to become obsolete in the near future (Parente et al., 2006; Fowler et al., 2018). According to a 2019 estimate, Oil & Gas UK predicted that the cost of decommissioning infrastructure on the UK continental shelf will be £51 billion.

How is decommissioning relevant to marine mammals?

Offshore decommissioning is a complicated, multi-disciplinary, costly, and energy-consuming process, involving activities such as installation preparation, well plugging and abandonment, conductor removal, mobilisation and demobilisation of derrick barges, installation removal, pipeline and power cable decommissioning, materials disposal and site. All these activities generate underwater noise, which has potential to impact marine mammals such as seals, whales, dolphins, porpoises, and sirenians (manatees and dugongs).

Are marine mammals protected by law during my decommissioning project?

Regardless of decommissioning project location, there are laws protecting marine mammals. In the UK for example, marine mammals are protected by law under the UK Wildlife & Countryside Act (1981). Other agreements/rules/statutes etc. apply such as the Agreement on the Conservation of Small Cetaceans in the Baltic & North Seas, ASCOBANS (1992), European Habitats & Species Directive (1992), Offshore Marine Conservation Regulations (2007 & amendments) – beyond 12 nm, Offshore Petroleum Activities (Conservation of Habitats) Regulations (2001), and Conservation of Habitats & Species Regulations (2010) – within territorial waters. 

How do I plan for marine mammals during my project?

Ocean Science Consulting Limited works worldwide, but the UK has taken the lead concerning decommissioning and marine mammals, and many countries are adopting these measures. In the UK, the Department for Business, Energy & Industrial Strategy (BEIS) provides regulatory guidance on decommissioning and marine mammals. It is then very important to design an appropriate Marine Mammal Mitigation Plan (MMMP; often required as part of the licencing process) prior to starting a project. This assesses whether marine mammals are likely to be present near the structure, considers any species’ seasonal trends, such as breeding, calving/pupping, and migration. A good MMMP also investigates likelihood of injury or disturbance from specific activities. This ensures that the whole project is feasible operationally, without breaching regulatory procedures, or worst, contravening law. 

What personnel or equipment do I require for my decommissioning project?

If your project involves explosives, cutting, or any activity that generates excessive underwater noise, then regardless of project location, it is advisable to plan the work at a time of least disturbance. It is important to consider the following mitigation measures:


In sensitive areas (such as Special Areas of Conservation, SACs), real-time monitoring of underwater noise is prudent as well as pre-operation acoustic propagation modelling

Do I really need PAM?

In periods of poor visibility and/or bad weather, or if your operations are likely to continue into the night, the use of PAM is recommended. Most operations in the world today use PAM, regardless of project sensitivity.

Alternative use of offshore installations

Ocean Science Consulting’s core research programme is to provide a solid evidence base to support converting offshore oil and gas drilling rigs and production platforms into artificial reefs for wildlife. Over a decade of research on measuring and modelling underwater noise and monitoring harbour porpoises (Phocoena phocoena) and their prey around offshore O&G installations has shown marine mammals use rigs and platforms as feeding stations, and these structures are diverse habitats in themselves (Todd et al., 2009a; Todd et al., 2009b; Todd, 2013; Todd et al., 2016; Todd et al., 2018; Todd et al., 2020a; Todd et al., 2020b; Todd et al., 2020c; Todd et al., 2021; McLean et al., 2022) – see our publications page for more information. This alternative decommissioning solution has been implemented in several areas globally, including the Gulf of Mexico, but not yet adopted in the North Sea. We are aiming to provide a robust evidence base to inform future decommissioning of North Sea offshore infrastructure.


Fowler, A.M., Jørgensen, A.-M., Svendsen, J.C., Macreadie, P.I., Jones, D.O., Boon, A.R., Booth, D.J., Brabant, R., Callahan, E., Claisse, J.T., Dahlgren, T.G., Degraer, S., Dokken, Q.R., Gill, A.B., Johns, D.G., Leewis, R.J., Lindeboom, H.J., Linden, O., May, R., Murk, A.J., Ottersen, G., Schroeder, D.M., Shastri, S.M., Teilmann, J., Todd, V.L.G., Van Hoey, G., Vanaverbeke, J., and Coolen, J.W. (2018): Environmental benefits of leaving offshore infrastructure in the ocean. Frontiers in Ecology and the Environment 16, 571-578.

Parente, V., Ferreira, D., Moutinho dos Santos, E., and Luczynski, E. (2006): Offshore decommissioning issues: Deductibility and transferability. Energy Policy 34, 1992-2001.

Todd, V.L.G., Pearse, W.D., Tregenza, N.C., and Todd, I.B. (2009a): Diel echolocation activity of harbour porpoises (Phocoena phocoena) around North Sea offshore gas installations. ICES Journal of Marine Science 66, 734 – 745.

Todd, V.L.G., Todd, I.B., Lepper, P.A., and Tregenza, N.C. (2009b): Echolocation activity of harbour porpoises (Phocoena phocoena) around an offshore gas production platform-drilling rig complex. Fifth International Conference on Bio-Acoustics, 31 March – 2 April 2009, 31st March – 2nd April 2009, Holywell Park, Loughborough University, UK, pp. 8.

Todd, V.L.G. (2013): Rigs – to decommission or not to decommission? Marine Scientist 43, 22-25.

Todd, V.L.G., Warley, J.C., and Todd, I.B. (2016): Meals on wheels? A decade of megafaunal visual and real-time Passive Acoustic Monitoring detections from on-tow and stationary offshore oil and gas rigs and platforms in the North and Irish Seas. PLoS ONE 11, 25.

Todd, V.L.G., Lavallin, E.W., and Macreadie, P.I. (2018): Quantitative analysis of fish and invertebrate assemblage dynamics in association with a North Sea oil and gas installation complex. Marine Environmental Research 142, 69-79.

Todd, V.L.G., Lazar, L., Williamson, L.D., Peters, I., Cox, S.E., Todd, I.B., Macreadie, P.I., and McLean, D.L. (2020a): Underwater visual records of marine megafauna around offshore anthropogenic structures. Frontiers in Marine Science 7, 230.

Todd, V.L.G., Ruffert, M., Williamson, L.D., Jiang, J., Cox, S.E., and Todd, I.B. (2020b): Proximate underwater soundscape of an offshore petroleum-exploration jack-up drilling-rig: relevance to harbour porpoise (Phocoena phocoena). Journal of the Acoustical Society of America In Review, 20.

Todd, V.L.G., Williamson, L.D., Cox, S.E., Todd, I.B., and Macreadie, P.I. (2020c): Characterising the first wave of fish and invertebrate colonisation on a new offshore petroleum platform. ICES Journal of Marine Science 77, 1127-1136.

Todd, V.L.G., Susini, I., Williamson, L.D., Cox, S.E., Todd, I.B., McLean, D.L., and Macreadie, P.I. (2021): Characterising the second wave of fish and invertebrate colonisation and production potential of an offshore petroleum platform. ICES Jounal of Marine Science 78, 1131-1145.

McLean, D.L., Ferreira, L.C., Benthuysen, J.A., Miller, K.J., Schläppy, M.-L., Ajemian, M.J., Berry, O., Birchenough, S.N.R., Bond, T., Boschetti, F., Bull, A.S., Claisse, J.T., Condie, S.A., Consoli, P., Coolen, J.W.P., Elliott, M., Fortune, I.S., Fowler, A.M., Gillanders, B.M., Harrison, H.B., Hart, K.M.L., Henry, L.-A., Hewitt, C.L., Hicks, N., Hock, K., Hyder, K., Love, M.S., Macreadie, P.I., Miller, R.J., Montevecchi, W.A., Nishimoto, M.M., Page, H.M., Paterson, D., Pattiaratchi, C.B., Pecl, G.T., Porter, J.S., Reeves, D.B., Riginos, C., Rouse, S., Russell, D.J.F., Sherman, C.D.H., Teilmann, J., Todd, V.L.G., Treml, E.A., Williamson, D.H., and Thums, M. (2022): Influence of offshore oil and gas structures on seascape ecological connectivity. Global Change Biology In Press.

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