Deployment of a Low-Cost, Motion Triggered Stationary Underwater Stereo Camera for Sampling Rockfish in Untrawlable Habitats

Underwater cameras are an increasingly important tool for assessing fish abundance and species composition in untrawlable habitats.  Increased use of stereo cameras in recent years has allowed fish to be measured with greater precision.  In most circumstances, artificial illumination is required to collect images, resulting in potential biases due to fish to the lights.   We present a new, less intrusive, underwater stereo camera modeled after camera traps used in terrestrial environments.  The camera is triggered by movement by monitoring the camera’s view field for potential targets with far-red illumination invisible to most fishes.  The camera system was designed to be low-cost by incorporating off-the-shelf commercial camera and computer components.  First field use consisted of deploying six units on Zhemchug ridge in the eastern Bering Sea. The camera units collected data for 12 hours, imaging  over 1800 fishes, mostly northern rockfish (Sebastes polyspinis, 37.7 %) and Pacific cod (Gadus macrocephalus, 10.4 %).  The length of the camera deployment allowed comparisons of fish abundance and behavior between night and daytime.  Three-dimensional  scene reconstruction using stereo images provided estimates of fish position relative to the seafloor, a critical component in evaluating the potential for hydroacoustic surveying of fish abundance in untrawlable habitats.