Whale Wise Listening lines
Testing the feasibility of affordable hydrophones deployed on fishing gear for cetacean monitoring
Acoustic monitoring is a key component of cetacean research but is often limited by the cost of equipment and deployment in challenging marine environments. This limits the quantity of scientific data collected and represents a barrier to small research groups with limited funding. To break down these barriers, we tested the feasibility of using a small, affordable hydrophone – called a HydroMoth – for cetacean acoustic monitoring. We also trialled their novel deployment on static fishing gear off the east coast of Scotland. In collaboration with the University of Edinburgh, St Abbs Marine Station and the Scottish Association for Marine Science.
Background
Owing to their underwater lives, monitoring cetaceans is a big challenge. Visual surveys are limited in their effectiveness and environmental conditions often prevent us seeing cetaceans at the surface. In contrast, hydrophones (underwater microphones) allow us to listen to cetaceans year round – whales, dolphins and porpoises are often very vocal, using sound to navigate and communicate in their marine environment. We can use this to determine cetacean occurrence, species diversity and behaviour, and how these vary in space and time. As a result, acoustic monitoring is a widely used and key component of cetacean research – hydrophones can be deployed on the seabed for years at a time and we have used hydrophones to listen for cetaceans in Iceland.
However, hydrophones and associated equipment for deployment and recovery can be very expensive, often totalling tens of thousands of pounds. This limits the number of hydrophones that can be deployed and the amount of data that can be collected. It’s also a risky business – hydrophone deployments are frequently lost at sea, resulting in the loss of precious data and equipment. As a result, many research groups struggle to afford hydrophones, limiting the research capacity of small institutions in particular. As a result, there is increasing interest in affordable acoustic monitoring technology and alternative deployment methods to improve research capacity to inform conservation.
Aims
To test feasibility of an affordable acoustic deployment to monitor cetaceans, we have the following research questions:
- Can a small, affordable hydrophone (called a HydroMoth) be used to reliably record cetacean vocalisations?
- Can we deploy HydroMoths on static fishing gear as an alternative to expensive seabed deployments?
- Are fishers interested in contributing to this research?
Project details
HydroMoths are affordable (~£100) underwater sound records developed by Open Acoustic Devices, following the success of their land-based AudioMoths. Consisting of a small recorder and a simple waterproof housing based on GoPro, HydroMoths have been used to monitor ecosystems such as coral reefs and seagrass and there is increasing interest in their application to cetacean research. To test their feasibility, research was conducted at St Abbs Marine Station, on the southeast coast of Scotland, by an MSc Marine Systems and Policies student from the University of Edinburgh, Sarah Kane.
To test the ability of HydroMoths to record cetacean sounds, we placed a HydroMoth and a SoundTrap (a more expensive hydrophone that is regularly used for cetacean monitoring) together in a tank. We then played sounds at different frequencies and in different positions around the hydrophone. Recordings from the HydroMoth and the SoundTrap will be compared to assess the cheaper model’s performance.
Acoustic deployments are limited not only by the acoustic equipment, but also the expense of deploying it. Working with fishers to deploy on static fishing gear could represent a possible solution; if successful, this could provide thousands of affordable deployment sites around the world. Therefore, we worked with fishers in St Abbs to deploy our hydrophones on creel pots (aka lobster pots) off the coast of Scotland to assess whether this is a practical solution and whether we could hear any cetaceans! We also surveyed fishers for their interest in contributing to research and monitoring in this way. Commercial fishing is a major threat to cetaceans and better understanding their occurrence around fishing gear could help us to develop solutions to mitigate entanglement and bycatch.
Project updates
With the MSc project now complete, we are working to collect more survey data from fishers and publish our results. We intend to continue this work into the future, exploring alternative forms of deployment in different areas and possible modifications to hydrophone design. Stay tuned!