Journal
MARINE ECOLOGY PROGRESS SERIES
Volume 395, Issue -, Pages 109-118Publisher
INTER-RESEARCH
DOI: 10.3354/meps08174
Keywords
Mesopelagic; Diel vertical migration; Swimming behavior; Target tracking; Benthosema glaciale; Moored echo sounders
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We deployed an upward-facing echo sounder mounted on the bottom and cabled to shore in a similar to 400 m fjord location for long-term studies of small mesopelagic fish and their potential predators. The population of the myctophid Benthosema glaciale displayed diverse diel vertical migration (DVM) behaviors, including normal DVM to surface waters at night, reverse DVM in the lower part of the water column in which fish ascended to similar to 200 m at day, as well as nonmigration of some individuals. The relative prevalence of these behavioral modes varied with season. Acoustic target tracking of individuals in deep water showed that B. glaciale was conspicuously inactive and drifted back and forth with weak tidal currents, essentially acting as plankton. Swimming was largely restricted to infrequent short bouts. More active swimming occasionally occurred in the vertical direction, and then in a stepwise pattern. Potential predators in deep water were swimming at speeds of <0.5 body length s-, with maximum speeds of similar to 1 body length s(-1). These results show that submerged echo sounders provide a means of non-intrusively studying both individual and population behavior of deep-living organisms.
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