My Account
Eavesdropping on the ocean may seem like an unlikely occupation, but Leigh-based researcher and university lecturer Dr Craig Radford believes it could help to better manage snapper stocks and save marine species such as the Bryde’s whale. Dr Radford was recently awarded an $800,000 Rutherford Discovery Fellowship, which recognises him as an emerging scientific leader in NZ. Over the next five years, he and his team will work on using passive acoustics to listen to the marine environment and monitor the health of ecosystems in the Hauraki Gulf. Dr Radford told Jannette Thompson that the fellowship will provide a welcome return to field work ….
I started my PhD in acoustics in 2004, at Auckland University, which is what first brought me to Leigh. My study focused on how marine animal larvae use sound as an orientation cue, a bit like a homing device. When crabs, fish and lobster reproduce they have a pelagic or open water phase, when the babies are off-shore. This can range from a few hundred metres to tens of kilometres. We’re trying to find out what sound cues guide these little guys back to the coast. To do this, we have to know as much as we can about the sound environment and we do this by recording and listening to the sea, and trying to understand the patterns. There’s also the sensory aspect – we’re trying to find out how well the larvae can hear and over what distances they can detect sound. A lot of work has already been done in this field. For instance, we know that during the night fish will swim towards a sound, while during the day they’ll swim away from it. Likewise, reef crabs will settle in response to reef sounds, but won’t to the sound they’d hear at say Pakiri Beach.
Typically, when you do your PhD you’re always out in the field. As you progress further through your academic career, you spend more time supervising other students’ work. The benefit of the Rutherford grant is that it’ll cover about 85 percent of my time, so I’m looking forward to spending more time collecting data. The hard part will be figuring out what it all means. Human activities like shipping, recreation and exploration are all increasing the amount of noise in the sea. The estimate is that since 1970, the ambient noise in the ocean has doubled with increased shipping being the main cause. We believe there is the potential for this increase in noise to affect the lifecycles of some animals.
In international terms, NZ waters are quiet and this is what makes it such a great place to study. The gulf is like a living laboratory. It has one-quarter of the world’s whale and dolphin species, as well as being a place which is visited by a lot of seabirds. Also, the majority of endemic fish of NZ that produce noise live in the gulf. This means we can observe the natural behaviour of the animals, but there is still enough shipping for us to begin to understand its effects. We’ll be spending the next five years monitoring both human and biological noise, and their interactions, to understand more about the health of the gulf’s marine ecosystems.
We hope that what we learn will help us to better manage the noise environment of the Hauraki Gulf. This may mean introducing a mitigation plan for the Bryde’s whale, for instance, and for this I’ll be working with researcher Rochelle Constantine. The Bryde’s whales swim on the surface so are very susceptible to ship strike. A mitigation plan may mean slowing ships down or putting some acoustic deterrent devices out to scare the whales away when ships come near. But there’s an economic cost in slowing ships down and an acoustic device may affect other animals so there’s a lot of work to do to work out the best solutions. And it’s not just about shipping. Small boats in large numbers could be a problem and any large coastal activity has potential impacts. It’s already been shown that underwater turbines for renewable energy can affect the settlement patterns of crustaceans. What effect, for instance, will the dredging and pile driving necessary to build a marina at Sandspit have on marine animals in that area? It could eventually mean that resource consents have to take into account the underwater soundscape.
Underwater acoustics is a relatively new field. We really only started listening to the ocean in World War II when they were trying to track down submarines. By the 1970s we knew that fish could hear, but we only learned that larvae could use sound to return to the coast in the last decade. More recently, we’ve noted that when fish start schooling, it produces a noise which, we believe, attracts larger predators. In turn, when they start rounding up the fish and forcing them to the surface, it attracts seabirds. They start to dive on the fish and that sound attracts the whales and large pelagic fish like sharks. We think this whole chain of events is mediated by sound. As part of the Rutherford research we’ll put listening stations in the gulf, which will help us identify what animals are making noise and what the different sound signatures are at the different stages of this process. We’ll then model how shipping activity could be masking these sounds and how this might affect feeding behaviours.
What we’re learning about fish recruitment rates will also contribute to the debate on how to best manage fish stocks, which includes setting quota in the snapper industry. We need to understand fish behaviour and what the larvae are doing, if we are to properly manage the adults. Potentially, sound could also be used to enhance settlement. For instance, after an event like an oil spill, once the environment is cleaned up, sound could be used to attract animals back to the area by playing the correct orientation cues.
All good research leads to more questions than answers and scientists are naturally hesitant to definitively say “this is what’s happening”. Trying to balance recreational and commercial fishing demands, with what the environment can sustain, is tricky. I can probably trace my interest in marine biology back to fishing and whitebaiting trips with by grandfather, in Taranaki, and I believe it’s important for children to continue to have these experiences. I love taking my family out fishing, but we only ever take what we need for dinner that night. The pressure from both commercial and recreational fishing interests in the Hauraki Gulf is already high so I guess I think taking just enough for a feed is the right thing to do. NZ has been a world leader in the way it’s managed its fisheries – the quota system was quite revolutionary at the time. But, there’s always bits where it falls down because we don’t know enough about the biology of the animal. That’s where I hope this study will be of some use.
