Fig. 8
The time of day when periodic descents occurred in UTC time, top panels, and related to the photoperiod, bottom panels for females during the spawning periods. Shading indicates approximate nighttime hours on the median day of the spawning period. In the bottom panels circles indicate expected number of descents during night and day if their timing was randomly distributed, based on the photoperiod lengths of day and night for March 1 (Western Norway) and March 15 (Mid Norway), i.e. the median calendar day of the spawning period in each area.
