What Can Underwater Video Tell Us about Selectivity and Catchability? in Situ Observation of Spot Prawn (Pandalus platyceros) Traps in Deep Water

Direct observation of fishing gear deployed under water is an increasingly popular technique for understanding the processes that determine the gear’s final catch. Underwater cameras have been extensively used to observe trawl gear, but is increasingly being applied to traps and pots. Most research to date has been conducted in shallow water, with camera placement assisted by teams of scuba divers – a technique unsuitable for the majority of trapping gears that are deployed in deep water. Here, we show how underwater cameras can be affixed to deep water traps to maximize the information that can be collected during a gear deployment. We explore parameters that can be measured from underwater video, and focus on direct measurement of catchability and selectivity. We present data from a field study in which we recorded traps targeting spot prawns (Pandalus platyceros) at ~100m depths, and demonstrate that catchability of prawns in traps is density dependent. Finally, we describe technical challenges that must be overcome by any researcher seeking to use underwater cameras to study deep water traps, and how these data can be used to improve the selectivity of fishing gear.