Vertical Distribution of Daily Migrating Mesopelagic Fish in Respect to Nocturnal Lights

摘要

The nighttime distribution of vertically migrating mesopelagic fish in relation tonocturnal light was studied during a circumglobal survey, in the Red Sea, and in a fjord athigh latitude. The study was based on data derived from ship borne echo sounders(circumglobal and the Red Sea) as well as using upward looking echo sounders mountedon the bottom (Masfjorden, Norway). We also applied a numerical model for analyzingdiel vertical migration patterns. The effect of the lunar cycle was the focus in studies atlow latitudes, while seasonal changes in nocturnal light climate was in focus at highlatitude. Lunar phase significantly affected the distribution of mesopelagic fish at theglobal scale and in the Red Sea. During nights near full moon, scattering layers ofmesopelagic fish distributed deeper than during darker phases of the moon. At highlatitude, mesopelagic fish switched its behavior along with seasonal changes in nocturnallights. In autumn, the population of the studied fish (Maurolicus mueleri) formedseparated layers. Juveniles performed normal diel vertical migration followed bymidnight sinking, with midnight sinking mainly related to temperature minima and alsofor avoiding predators. Meanwhile the adults did not migrate vertically, reducingforaging but increasing the adult survival. From late winter to mid-Spring, interruptedascents behavior was noted in the afternoon. Predator avoidance, satiation, and findingtemperature optimum might be the reason behind interrupted ascents. At lighter nights inmid-summer, M. muelleri took on schooling behavior, likely as an anti-predator behaviorpermitting access to the upper waters in the absence of darkness.