Research Technical Report

Estimating Inter-daily Variation in Fish Densities from Video Surveys Near Monterey, CA

Mohay, J.L., R. Starr, M. Gleason, K. Cieri, and R. Fields (November 2020)

Oral presentation at the Western Society of Naturalists Annual Meeting, November 5-8, 2020, Virtual Meeting

ABSTRACT

Visual surveys are often used to assess habitats, species populations and changes among them over time. A common assumption when conducting visual surveys for population dynamics is that, although there may be seasonal variation, there is little daily variation. This implies that differences observed among survey days are due to spatial, not temporal, variation. In June 2019, in collaboration with the Monterey Bay National Marine Sanctuary, we spent 5 consecutive days surveying Portuguese Ledge, Monterey, CA to assess inter-daily variation of benthic fishes. We used the BOSS video lander, a 9-camera system with fiberoptic tether that enabled viewing and recording of fishes at the surface. We deployed the lander on high-relief habitats selected using multibeam maps and recorded 3-minute videos at 93 sites from June 25-28. We analyzed the video using EventMeasure (SeaGis, Australia) counting each species at a MaxN frame and measuring total lengths. Average densities estimated at Portuguese Ledge were not significantly different among days for any species except Ophiodon elongatus and Sebastes levis. There was a significant difference in average density among days for pooled ground species of interest.