Swimming Speed and Metabolic Rate during Routine Swimming and Simulated Diel Vertical Migration of Sergestes similis in the Laboratory

Abstract

Sergestes similis (Hansen, 1903) is a common mesopelagic vertically migrating shrimp common in the temperate and subarctic North Pacific Ocean. The species is a diel vertical migrator, although it remains primarily above the oxygen minimum layer in regions such as off California where the layer is well developed. This shipboard study with a computer-controlled swim tunnel provided the first continuous examination of this species' swimming behavior and metabolism over a 24-hr cycle. Sergestes similis swam at a routine speed of around 4.4 to 4.95 cm sec-I. Burst speeds ranged from 14 to >20 cm sec-1. Swimming speeds during the day, at low temperatures simulating those at daytime depths, were similar to those at night at the higher temperatures characteristic of the surface. Night metabolic rates were higher than in the day, especially during the early night when most feeding activity may take place. Swimming speeds during times of simulated vertical migration averaged slightly faster than those of routine day or night swimming, averaging 6.2 cm sec- l during the time of upward migration and 5.4 cm sec-1 during simulated downward migration, but the difference was not significant. Downward migration is not accomplished by passive sinking. Calculations based on observed swimming activities and metabolic rates indicate that vertical migration confers a clear metabolic energy savings to S. similis over remaining resident in surface waters, though this result may not be applicable to other vertical migrators and is likely moderated by decreased feeding opportunities at depth.