Fish use of deep-sea sponge habitats evidenced by long-term high-resolution monitoring

It is critical that fish's habitat uses of benthic habitats are understood, to inform effective fisheries management and to predict the impacts of human activities and climate change. In this study, benthic landers were used to collect long-term high-temporal resolution data to gain insights into the habitat use of sponge grounds by fish at the Sambro Bank Conservation Area. An integrated ecosystem-based monitoring approach was used, involving data collected on the biology, food supply, and oceanography. Fish abundance, behaviour and complex benthopelagic interactions were analysed over spatial and extended temporal scales (i.e., 30-min intervals from 2021 to 2023). A total of 21 different planktivorous and benthivorous fish taxa were found to utilise the seafloor. We show that sponge grounds can act as a nursery, feeding and shelter habitats for commercially important fish. In-depth analyses of Redfish, urophycid hakes, and Silver Hake revealed distinct diel and seasonal patterns and showed how food, sponge density and current speed are important drivers of their abundance and behaviour. Supported by fishery trawl survey reports, high-temporal resolution benthic ecosystem monitoring revealed the importance of sponge grounds and environmental drivers to commercially important fish. Such information is crucial for developing and implementing robust, evidence-based policy and management.