Fish behavior in response to an approaching underwater camera

Responses of fish to camera survey gear can influence abundance estimates, and fish behaviors such as attraction or avoidance of an approaching camera platform can bias fish counts. In addition, artificial lighting is generally required for camera-based surveys in boreal systems at > 30 m depth. This study recorded the responses of fish and their apparent orientation as seen in camera images taken in two different areas in Alaska. Stereo-image methods were used to estimate fish movement, range from camera, and the movement of the camera platform itself by estimating the spatial relationship between fish and the seafloor. Change in the apparent position of feature points along the seafloor and the fish was used to derive fish and camera speed. A total of 670 individual fish across 19 near-bottom species were analyzed from a dataset of 3463 image frames from 112 separate camera deployments. Individual fish species were combined into groups and analyzed for reactions, orientation toward the camera, nearest approach to the camera, and swimming speed. Most fish did not react strongly to the camera. A number of distinct patterns in reactions were observed, with roundfish exhibiting the highest level of attraction to the camera and flatfish showing the highest number of strong avoidance reactions. Significant differences in approach distance and fish swimming speed across analysis groups, reactions and regions were found, with highest fish speeds observed with roundfish and closest approach of the camera observed with demersal rockfish and flatfish. The findings demonstrate distinct differences in reactions among groups and suggest that the potential attraction response of roundfish might lead to positive biases for density. Flatfish were reactive mostly at close ranges, and rockfishes exhibited neutral and moderate reactions, which may signal reasonable estimates of abundance for these groups using camera-based surveys.