Strong site fidelity, residency and local behaviour of Atlantic cod (Gadus morhua) at two types of artificial reefs in an offshore wind farm

Globally, biogenic temperate reefs are among the mostthreatened habitats. In the North Sea in particular, largeshellfish reefs were lost owing to fishing activities in the1900s. The impact of offshore wind farms (OWFs) on marinewildlife is extensive, and it offers the possibility to reintroducenew hard substrate habitats that are protected from fisheriesat a large scale. In addition to the submerged structures ofOWFs, marine hard substrate habitat can be further enhancedby providing extra artificial reefs. In an operational OWFalong the Dutch coast, four artificial reefs (two with a scourbed and two without) were deployed in the vicinity of awind turbine. Acoustic telemetry was used to monitor thefine-scale movement of 64 Atlantic cod (Gadus morhua). Themonitoring ran from July 2021 to January 2023. Detailedinformation on behaviour, area utilization and attractionto the structures was determined. Results showed strongattraction (high site fidelity and residency) to the artificialreef, with no significant difference between the two testedtypes of reefs, and only a few individuals staying over winter.Cod spent a large proportion of their time hiding in theartificial reefs, suggesting that adding pipes for shelter has abeneficiary effect.