Developing an Optical Survey for Georges Bank Yellowtail Flounder

Yellowtail flounder (Limanda ferruginea) is an important target and bycatch species on Georges Bank. In response to uncertainty in recent yellowtail biomass estimates we developed a new optical survey technique. A live feed video camera is placed in a open trawl net, which was developed with fishermen, to record fish species passing through along with periodically closed tows to collect biological data. Our objective is to investigate the abundance, spatial distribution, and biological characteristics of yellowtail flounder and other groundfish species. Over one hundred hours of video footage were obtained from past surveys. The average yellowtail and standard deviation (SD) per tow were 249 (151.2), 91 (76.1), and 195 (90.9) for fall 2013, spring and fall 2014, respectively. While the video is informative, the vast amount of footage collected presents analytical challenges. Independent observers watched video from each sampling tow in one-minute intervals viewed at half speed. Counts of flatfish observed in the video were compared to catches in the net. The accuracy regarding tows categorized as having low, medium, and high visibility were 51%, 84%, and 92% respectively. A number of sampling techniques have been investigated to determine the most accurate and precise method to analyze the videos.