Artificial reefs in offshore wind farms seem to be beneficial for cod. Cod seem to be attracted by the reefs and even stay there for longer periods of time, more so than with conventional erosion protection. This is according to a from a study by Wageningen University & Research.
These findings have been published in the scientific journal Royal Society Open Science. The study offers important insights into whether species can benefit from the reintroduction of hard substrate in wind farms in the North Sea.
Artificial reefs in Borssele 1&2 wind farm
Following the construction of the 2020 Borssele 1&2 wind farm, four artificial reefs were installed around a single monopile within the wind farm. Following this installation, Ørsted and Wageningen University & Research conducted a monitoring programme on Atlantic cod in 2021 and 2022 to study the use of the artificial reefs and the behaviour of the animals around them.
The reefs consist of 45 concrete tubes of different sizes. More than 60 cod were caught at the reefs and fitted with acoustic transmitters. In addition, 16 receivers were installed around the artificial reefs to ‘hear’ and monitor the tagged cod. Data from the transmitters provided detailed insights into the movement and behaviour of the tagged cod.
The results showed that most of the fish stayed near the reefs for long periods of time. The researchers also observed that the cod spent a lot of time hiding in and around the concrete pipes. This gives the impression that these structures play an important role as foraging areas and hiding places.
Artificial reefs more attractive than conventional erosion protection
This study provides valuable insights on nature inclusive construction in wind farms and creating suitable habitat for North Sea species. The artificial reefs were more attractive to cod than the stones around the monopiles. This is because the cod piles offer much larger openings, providing shelter for cod. Two of the four artificial reefs were installed on a layer of stones and two directly on the sandy seabed. Cod were attracted equally by both designs.
Return of reefs: a way to contribute to the recovery of North Sea species?
Wind farms can have a negative impact on marine life during construction and operation, for example through underwater noise, electromagnetic fields and habitat degradation. However, according to Benoît Bergès, principal researcher and marine biologist at Wageningen Marine Research, there is potential for a positive contribution by creating suitable habitats. ‘I am really looking forward to further investigating the food availability and energy consumption of fish around artificial reefs and to determine whether these reef structures actually lead to increased fish reproduction and ultimately benefit the fish population.’ Source: Ørsted Screenshot from video. Source: Ørsted
