UC San Diego

Marine protected areas (MPAs) have been established worldwide to protect coastal ecosystems and the species inhabiting them. However, it is difficult to quantify whether these areas are adequately protecting the targeted species. Current monitoring methods, such as diver surveys, allow fish species to be identified in situ, but are known to alter fish presence and behavior. Other methods, such as acoustic telemetry, are relatively invasive, requiring the implantation of a transmitter tag into the fish. Additionally, both these approaches are laborious and expensive, relying on good weather and a talented pool of fisherman and divers. Methods that are non-invasive, such as passive acoustics, offer good spatial and temporal coverage, but ascribing specific calls or sounds to the species creating them is difficult, particularly for fishes. Camera deployments allow for in situ observations of behavior, diversity and frequency of occurrence of a wide variety of animals but are often hindered by low-light and battery limitations. Here, I developed passive acoustic and optical imaging tools to study sound-producing fish that allow improved performance over contemporary methods. These tools were used to study chorusing fish in protected kelp forests along the southern California coast. First, an autonomous Wave Glider was equipped with a passive acoustic recorder to map the distribution of five soniferous fish spawning aggregations. The fish choruses started near sunset and ended before sunrise, and were almost exclusively recorded offshore of kelp forests. Second, a low-cost underwater optical imaging system that utilizes a consumer-grade camera to capture high-quality images in low-light aquatic habitats without artificial lighting was designed and developed. The system was used to captured >1,500 images per day over 14 days, which revealed biologically important behaviors as well as daily patterns of presence/absence. Lastly, an underwater controlled source of known position was used to improve an acoustic localization algorithm to track fish to a resolution of a few meters. The fish remained outside of the MPA while vocalizing. This work demonstrates the promise of these tools to non-invasively monitor animal behavior, biodiversity and frequency of occurrence in MPAs as well as other nearshore areas.