A new technique for periodic bait release at a deep-sea camera platform: first results from the Charlie-Gibbs Fracture Zone, Mid-Atlantic Ridge
Direct time-series observations of deep-sea biological activity are largely restricted to passive observations of benthic epifauna using unbaited time-lapse camera systems. However, highly mobile fauna such as scavenging fish are not generally observed at unbaited instruments. Here, we describe the successful adaptation of existing baited camera technology to incorporate an autonomous periodic bait-release system. This technology enables long-term high-frequency time-series observations of deep-sea scavenging demersal fish and crustaceans to be made for the first time. The periodic bait-release system was deployed to 3664 m in the Charlie-Gibbs Fracture Zone, Mid-Atlantic Ridge, for 38 days and incorporated six individual bait-release events. The arrival/departure pattern of Munidopsis spp. and macrourids at the camera was indicative of successive responses to individual small baits. A mean macrourid population density estimate of 8 fish km(-2) was calculated from first-arrival times at successive releases. The arrival pattern and lingering behaviour of zoarcids were comparable to observations at more persistent large food falls. Seventy-four percent of observed zoarcids were < 100 mm in total length, and it is suggested that the location of the deployment in the Charlie-Gibbs Fracture Zone may be of importance as a zoarcid breeding site or nursery ground. Small, possibly juvenile, Coryphaenoides armatus were also observed infrequently. The periodic bait-release design has potential for further development.