Fig. 1. The mean submergence duration recorded during 6 h intervals for 12 green sea turtles as they migrated from Ascension Island to Brazil. , night; , day; +, 6 h periods that straddle dusk and dawn. Four periods of long submergences (between 55 and 67 min) in F are plotted as 50 min to allow equal scaling of the y-axis in the different plots while maintaining easy visual comparison between the different parts of the figure.