The Influence of Bait and Stereo Video on the Performance of a Video Lander as a Survey Tool for Marine Demersal Reef Fishes in Oregon Waters

Abstract

Abstract: We evaluated how the use of bait as a fish attractant influenced the species and size composition of demersal fishes viewed with a stereo video lander at 160 sampling sites at Stonewall Bank, a deepwater rocky reef complex off the Oregon coast. We also studied the effectiveness of stereo video for generating estimates of fish length and distance from the cameras. Bait altered the species composition of fish encountered, increasing the mean counts of demersal fishes by 47%, with increases of 135–250% for Rosethorn Rockfish Sebastes helvomaculatus, Northern Ronquil Ronquilis jordani, and Spotted Ratfish Hydrolagus colliei. Increases in the mean counts of 35–150% for unidentified sculpins (Cottidae), Yelloweye Rockfish S. ruberrimus, and Quillback Rockfish S. maliger were nonsignificant. The calibrated stereo video lander provided acceptably precise estimates of fish length and camera-to-fish distance (range of three replicate measurements less than 3 cm for length and 20 cm for distance) for 34.3% of the demersal fishes that were counted. The precision of length and distance estimates declined with increased distance; acceptable estimates of distance were typical when fish were within 200 cm and were infrequent when fish were beyond 500 cm. Bait reduced the mean distance at which acceptable estimates of length and distance were obtained from 264 cm to 200 cm, but had no effect on mean fish length for the three most frequently encountered demersal species. The combined effect of bait on demersal fish counts and mean distance more than doubled the efficiency of the stereo video lander for generating fish length and fish–camera distance estimates. Received January 22, 2014; accepted April 9, 2014