Shining a light on fish at night: an overview of fish and fisheries in the dark of night, and in deep and polar seas

In aquatic environments, what one observes during the day can differ substantially by night. The species composition and associated ecological processes that occur during the day are often different than night. In polar seas and at great depths, "night" can span, months, years, and beyond. Teleosts and elasmobranchs have evolved unique sensory and behavioral modalities for living in darkness. As a consequence, fishers have adopted unique strategies for exploiting fish at night or in dark systems. We propose that neglecting the night has led to an incomplete understanding of aquatic organismal ecology, population/community dynamics, and ecosystem function with consequences for fisheries conservation management. To address this knowledge gap and stimulate the exchange of new data and ideas on behaviors, patterns, and processes relating to fish and fisheries in darkness, Fish at Night: an international symposium was held in Miami, Florida (USA), from 18 to 20 November, 2015. Here, we synthesize the findings from the symposium, providing an overview on the state-of-knowledge of fish studies in the dark, identifying critical information gaps, and charting a course for future research. We focus our commentary and synthesis on six areas: (1) nocturnal fish behavior and ecology; (2) fishing, fisheries, and enforcement; (3) deep and polar seas; (4) diel fish distribution and abundance comparisons; (5) methods for studying fish in darkness; (6) human threats to fish at night; and (7) larval fish at night. Taken together, we attempt to "shine a light" on fish at night, generating a greater interest and understanding of fishes and fisheries during darkness.