Piling it on

The world's biggest fish tank

The world's biggest fish tank!

29 June 2015 by Richard Hollingham

Renewable energy is an important part of the UK's energy mix and we need to know more about its effects on marine animals. Steve Simpson and Rick Bruintjes explain how they're using a home-made pile-driver to investigate.

Richard Hollingham: We're at a former shipyard at Blythe, just north of Newcastle. Steve, what is this experiment?

Steve Simpson: This is probably the biggest fish tank you have ever seen. It's 80m long, 20m wide, 3m deep with cod, plaice and crabs all getting on with their day-to-day business. We're looking at the impact of pile-driving noise on these animals. Pile-driving is used for building offshore, for example for wind farms, and there is a lot of uncertainty about how that might affect marine animals. So we've built an experimental piling rig, a small pile-driver driven by that tractor over there, which bangs on a 3m-long steel pipe set into the sediment at the bottom of this dry dock.

Richard Hollingham: What are all the ropes and wires slung across the dock here?

Rick Bruintjes: These are underwater microphones called hydrophones that pick up the noise of the pile driving. All the fish we put in have a little tag that pings at very high frequency and the hydrophones can detect this too, so they tell us where the fish are with an accuracy of approximately 20cm. Some fish also have heart-rate monitors and accelerometers that measure their tail beat.

Richard Hollingham: Why isn't the tractor running at the moment?

A crab

Steve Simpson: We're doing two hours on, two hours off for two solid days. After that we'll look at the movements of the fish and the information about their behaviour and physiological condition from the other monitors, and compare these for the periods of piling and the periods in between.

Our research is different from previous studies that have played recordings of pile driving using underwater speakers. In reality a lot of the energy is transferred directly into the sediment and with our piling rig we can look not only at the acoustics in the water but also at how that sound is propagated through the sediment. For the plaice and crabs that are on the seabed that's much more important than what is happening higher up in the water.

Richard Hollingham: Rick, what's the benefit of doing this on such a large scale?

Rick Bruintjes: The main question, which is a very simple but nobody has really answered, is do fish avoid noise? Using such a large aquarium we should actually be able to tell if the fish swim away from the noise, or are attracted by it or do anything else - they might freeze because of it or double their swimming speed. And we need to understand whether these effects are bad for the fish.

Richard Hollingham: There are several shipping containers here too, full of your equipment. Let's head in here to see the other part of the experiment.

Fiona here is an undergraduate working on the project. Fiona - on the bench you've got a basket from a deep-fat fryer with a plastic tub inside; what on Earth is this?

Fiona: We're going to put a crab or a mussel in each container, fill it with water and measure the oxygen content. Then we'll lower it into the dock, and measure the oxygen content of the water inside again after periods of quiet and periods of pile driving to compare how much oxygen the crab or the mussel has used. If they've used more oxygen during the piling phase it means their metabolic rate has got higher, which could indicate stress. I know it looks crazy but I think it will work - I'm hoping it will work!

Richard Hollingham: Back outside, looking at this tank again: if you imagine it as a fish tank it is vast but compared to the sorts of projects that are going on offshore, all the way round the British coast, it's still quite small. Can you get enough from this?

Steve Simpson: I think we get two things from this. The scale means we can look at animals moving naturally, and much more accurately replicate the acoustic conditions in the sea and the seabed. But we're also trialling technology that we could take offshore. And that's really our longer-term ambition: to see whether the pinger systems could be used at a larger scale, to see how the heart-rate monitors and accelerometers might work in a sea-pen or even with totally free-living animals.

The team

Richard Hollingham: Rick, this is increasingly relevant as we're seeing more and more offshore, particularly wind, generation, in the UK but also around Europe and the rest of the world.

Rick Bruintjes: That's right. The UK is definitely at the frontier of offshore wind energy. As we speak there are large areas where piles are being driven into the seabed for wind farms, which is a very good thing. But wind turbines can be up to 200m high, so the piles they use are on average 5 to 10m in diameter. You need a very big hammer to drive these into the seabed and it makes a lot of noise. Just how important that noise is, well, that is still to be found out.

Richard Hollingham: Steve, how important is this research given the state of the industry and the number of turbines being built?

Steve Simpson: I think the UK stands to be a global lead on offshore renewable energy. We are certainly a small island surrounded by energy-rich waters, whether it is tidal and wave or wind. But at the moment we're still not certain what effect the noise might have on certain species of animal and this means the industry is held up sometimes. We hope to generate evidence that will reduce that uncertainty so offshore renewable energy can fulfil its potential as part of our future energy budget.

And I guess the nice thing about noise as a pollutant is that we could stop it tomorrow; we can control noise in a way we can't control temperature, ocean acidification, chemical pollutants, micro-plastics. So you could choose simply not to make noise during a spawning season or to redirect a shipping lane if you've got a sensitive biological event. By providing the evidence that could help that decision-making we may soon be able to accelerate the development of renewable energy which is important if we're ever to meet our 2020 and 2050 obligations for carbon dioxide emissions.

This feature is adapted from the Planet Earth Podcast, 2 September 2014. It was recorded at the Offshore Renewable Energy Catapult - external link.

Dr Steve Simpson is a lecturer in marine biology and global change at the University of Exeter. Dr Rick Bruintjes is a NERC-funded marine renewable energy intern studying the impact of noise on fish behaviour in co-operation with the University of Bristol, University of Exeter and consultancy HR Wallingford.