How an underwater gas pipeline became a fish haven

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.

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.