Fish Spas: the importance of turbulence on stress levels of fish in dynamic environments.

The coastal marine environment is becoming ever more populated by the placement of infrastructure from industries including oil and gas and more recently the renewable energy sector including wind, wave and tidal energy devices. There are currently >4000 offshore wind turbines in Europe that have a monopile for a foundation (87%). For fish, these structures create new habitat, but the structures also change the hydrodynamic environment by introducing wake turbulence downstream of the structure. Fish are known to exploit small scale vortex structures at scales relevant to fish size. However, evidence suggests that fish also exploit wakes at much larger turbulence scales such as in the lee of a marine renewable device where vortex scales are significantly larger than fish length. These results suggest that fish respond as a direct result of physical changes in the environment at a range of scales. What is less clear is how changes in hydrodynamics translates to the physiological response in fish, primarily the stress response.

Hydrodynamics is a fundamental process in the marine environment and there is little information of how changes in flow environments (current speed or oscillatory flow) and associated changes in turbulence influence physiological processes of fish. The question therefore arises, does turbulence act as a fish 'spa'? The hypothesis is that turbulence diffuses the forces associated with flow velocity to act as a refuge behind marine renewable structures, especially in high flow environments allowing fish to exploit these environments. With the future addition of thousands of new structures into the marine environment, it is essential that the mechanism behind behavior changes is fully understood. Therefore, the aim of this project seeks to understand the importance of hydrodynamics on the stress response of marine fish using both controlled laboratory experimental and field based approaches.