Development of stereo camera methodologies to improve pelagic fish biomass estimates and inform ecosystem management in marine waters

Abstract

Abstract To understand and manage marine ecosystems, long-term monitoring of fish biomass is needed. A challenge in estimating fish biomass using sampling nets is varying catchability with habitat, weather, or vessel traffic conditions. Underwater stereo cameras have shown promise in providing a non-lethal, efficient, and cost-effective method to observe and measure fish in areas that cannot be sampled otherwise. These methods, however, have yet to be demonstrated for mid-water pelagic or semi-pelagic fishes. We designed, built, and tested a stereo camera for its potential to augment survey assessments of pelagic fish biomass in areas where trawl net samples cannot be collected. In a pilot test, the stereo camera was used to identify fish species and to measure fish length, depth, tilt, and yaw. Five paired stereo camera deployments and pelagic midwater trawl hauls were compared during an acoustic survey in the Strait of Georgia, British Columbia. Fish sometimes moved in response to the stereo camera deployment, but acclimated quickly to its presence at depth. Pacific hake, Merluccius productus, and walleye pollock, Gadus chalcogrammus, were the two dominant species in both midwater trawl haul catches and stereo camera images, but fish sizes were significantly larger in most cases in stereo camera images compared to trawl haul catches. Fish length measurements were most accurate when yaw angles were