Foraging behaviour and movements of an ambush predator reveal benthopelagic coupling on artificial reefs

Abstract

The behaviour of coastal fishes to new habitats and trophic opportunities provided by artificial reefs may reveal the key processes which sustain fish production at these reefs. We quantified the trophic link between benthic predators and pelagic forage fish from the movement and foraging behaviour of an ambush predator, the bluespotted flathead Platycephalus caeruleopunctatus, around an artificial reef in relation to schools of small pelagic fish. We used a network of acoustic receivers to monitor the fine-scale movements of 48 acoustically tagged flathead around 5 groups of artificial reef modules for 8 mo in conjunction with acoustic surveys of pelagic baitfish and sustained monitoring of current speed and direction. Flathead were highly associated with the artificial reef, with 44% of detections within 10 m of the modules. Flathead had a considerable degree of fidelity to the reef system, with an average residency period of 84 d yr-1 (residency index = 0.23, SD = 24 d). Low activity was recorded by accelerometers in the north-east of the artificial reef. This coincided with high densities of forage fish which were also found inside the stomachs of the flathead. Artificial reefs with high vertical relief allow planktivores to feed through more of the water column, fixing more pelagic biomass into the system. Defining the residency and trophic connectivity of fish at artificial reefs is critical to clarify the production-attraction debate and the sustainability of fishing at artificial reefs.