Integrating acoustics and video imaging to illuminate life in the mesopelagic

Abstract

The complementary strengths of acoustic and in situ visual sampling for understanding ocean life have been evident from the earliest days of each technique. The “deep scattering layer,” for example, was discovered using military sonars in the 1940s. This layer, thought at first to be the seafloor, was confirmed to be biological via in situ visual observations. This early example of combining these two powerful approaches highlights their complementary strengths (and weaknesses). Since then, acoustics and imaging have made great advances in both technology and application. Yet, they have been used together to address biological questions only infrequently, noting substantive contributions by Whitlow Au. Building on this foundation, we have been integrating acoustics and imaging to understand life in the mesopelagic. Used in a synergistic fashion, these tools allow us to describe the behavioral responses that animals exhibit to platforms and their lights, to measure the species-specific broadband “acoustic signatures” of pelagic animals needed to interpret remotely collected data, make measurements of animal size with a single camera, and examine how animal distributions are affected by the environment. In combining acoustics and imaging, there is power to observe biological phenomena in the ocean not fully resolvable with either technique alone.