Copepods in a hurry: Sustained high-speed upward migration’

Replicated data on the vertical migration of the copepod Metridia pacifica indicate that this 2-3-mm animal can maintain upward swimming velocities of from 30 to 90 m h-l for durations of more than an hour. Internal evidence in the data suggests that much of the variability within this range reflects differences in motivation of the animals, rather than sampling error. These data are apparently the greatest sustained swimming speeds ever sub-stantiated for any copepod and are larger by a factor of from two to ten than several previous field estimates for copepods. There are various reasons for an inter- this question, since at certain times of day est in the speed at which small aquatic their-population movements are strongly organisms propel themselves through the unidirectional. Past studies of the vertical water, including, for example, evaluation migration of small organisms, however, of the energetic costs of their normal based on time-series samples of the popu-swimming activity (Vlymen 1970; see also lation distributions in the water column, Klyashtorin and Yarzhombek 1973). In have often been handicapped by the rela