Mesopelagic fishes in a hurry at low latitudes

Abstract

We studied mesopelagic fishes in the Red Sea (22°N), hypothesizing that the rapid shifts between day and night at low latitudes would translate into rapid vertical migration speeds and brief near-surface ‘antipredation windows’. Using a bottom-moored echosounder, we found that diel vertical migration speeds of acoustical scattering layers were up to double that of the global average. Visits to upper water by some of the layers were strikingly brief, around 10 min, and included unusual rapid ascent and descent (up to 22 cm s-1), apparently with a high degree of behavioral plasticity. We suggest that the behavior of mesopelagic fishes in upper waters relates to their respective light sensitivities but is controlled by the arrival of predators. Rapid shifts between day and night appear to be an inherent factor in structuring marine ecosystems at low latitudes.