Comparison of video camera sled with diver surveys for queen conch Lobatus gigas density estimates in the west coast of Puerto Rico

Abstract

Queen conch Lobatus gigas is one the most important fishery species in the Caribbean. Currently, queen conch harvest is prohibited in the Exclusive Economic Zone (EEZ) in Puerto Rico. Since 1996, abundance estimates in Puerto Rico have been conducted by scuba divers at intervals of 5 yrs. Yet diver surveys are limited by depth and time. In contrast, underwater video or camera surveys are not constrained by these factors and also provide a permanent photo record of observations. We conducted a survey of queen conch density on the western shelf of Puerto Rico in 2016 using two different methods: divers and a camera sled. Divers surveyed eight transects of 2–3 km using diver propulsion vehicles and standardized, historical methods. The camera sled was fitted with a digital camera, synchronized strobe lights, and paired lasers, and was towed along the dive transects several days later. Conch densities (conch ha–1) estimated with the camera sled were significantly higher than those estimated by diver survey methods, while mean length was smaller. Both results were driven by the higher selectivity of the sled method for smaller conch. These results may lead to further applications or development of sled survey techniques, and improved data collection and analysis that can be used for management of queen conch in the Caribbean.