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As we celebrate World Environment Day, marine scientist Tim Cooper who works on mine and petroleum closures at BHP explains how a soon-to-be decommissioned gas pipeline off the coast of north-west Australia became a haven for endangered fish species, including green sawfish (critically endangered) and zebra sharks, as well other commercially important fish.


While you might expect an underwater pipeline should be removed once it becomes redundant, its removal may adversely affect marine ecosystems that have thrived while this subsea infrastructure has been in place. Extracting it can cause more environmental disturbance than if it is left in place.

In fact, where the seabed was relatively barren before the pipeline was laid, the pipeline itself may have been a catalyst for greater ecological diversity. It can help provide a habitat for corals and sponges to prosper, creating a breeding ground and home for commercial fish and endangered fish species.

My role at BHP is to support identification of the optimum closure outcomes for BHP assets once operations have ceased. Part of this involves understanding the environmental outcomes from the closure decisions we make. Managing subsea infrastructure closures can be particularly complex in this regard.

These results are hugely positive, and if we were to remove the pipeline, this undersea environment could be potentially lost and the seabed returned to sand.

A recent world-first research project on the BHP Griffin subsea gas pipeline undertaken with the University of Western Australia and co-ordinated by PhD researcher Todd Bond showed that the pipeline has a diverse fish community comparable to that described in the 1950s, an era before fish trawling.

In depths beyond 80 metres, we found the immediate area around the pipeline had two to three times the value of commercial fish than in surrounding areas. We found similar fish numbers in shallower depths.

Through this research we saw critically endangered fish species near the pipeline such as the green sawfish, along with over 20 endangered or threatened species such as the scalloped hammerhead, great hammerhead and zebra sharks. We also found the pipeline to have high numbers of valuable commercial fish such as goldband and saddletail snappers and red and spangled emperors.

These results are hugely positive, and if we were to remove the pipeline, this undersea environment could be potentially lost and the seabed returned to sand.

When the Griffin pipeline was laid in the 1990s, it provided an anchor for the sponges and corals to grow, providing habitat and protection for fish. It acted like an artificial reef.

Why did this happen? Between 1959 and 1990 demersal trawl fishing (trawl fishing close to the seabed) on the north-west shelf of Australia is likely to have impacted the sponges and corals on the seabed where these types of fish like to live. The practice effectively cleared the seabed and fish numbers are thought to have decreased as a result. When the Griffin pipeline was laid in the 1990s, it provided an anchor for the sponges and corals to grow, providing habitat and protection for fish. It acted like an artificial reef.

The Griffin pipeline is 30cm in diameter, 62km long, and transported gas from the Griffin Field to the Australian mainland, about 30km south-west of Onslow, WA. The Griffin field ceased production in 2009. 

The research used baited cameras to survey 42.3km of the pipeline up to a depth of 140 metres. We then compared these results with similar surveys undertaken up to 40 kilometres either side of the pipeline. Of key significance, we observed many more commercial fish around the pipeline than off-pipeline. More commercial fish means fisheries could benefit from leaving the pipeline as is.

With something like 2000km of pipeline across the resources industry on the north-west shelf between Exmouth and Dampier, I believe this kind of research is essential.

BHP is nearing a decommissioning decision on the Griffin pipeline and we continue to investigate the options available to us. The final decision will balance our values and obligations with environment, health and safety considerations and external expectations to achieve an optimised closure outcome. This is the same approach we take to all assets at BHP nearing the end of their economic life. It is nearly always a complex equation but I’m proud that the work I do helps deliver the best possible outcome.

 

About the author

Tim Cooper has been with BHP for nine years and has a PhD in Marine Science from James Cook University, Queensland. Tim is also an Adjunct Associate Professor at the University of Western Australia. He is passionate about marine ecosystems and water quality. Tim worked with University of Western Australia and Todd Bond to deliver a research paper on fish and the BHP Griffin gas export pipeline titled ‘The influence of depth and a subsea pipeline in fish assemblages and commercially fished species’. This paper was published in November 2018 and is available for download here.

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