Even though D. pulex was present in such low numbers in 1967, samples seemed to indicate that their maxima remained near 75 m. There was no observable migration of this species during this year.
Because of the larger population of D, & in 1968, graphic representation of its vertical distribution was possible. On July 24 and 25, 1968, a day maxima at 62.5 m descended to 87.5 m at night while large numbers of D. pulex also ascended into the shallower depth strata (Figure 8). The largest surface population was recorded at 0602 hours, just before sunrise. Juvenile D. pulex behaved in a way similar to the adults during this diel sampling period.
Figure 7. The die1 vertical distribution of Bosmina longispina on August 28 and 29, 1968, in Crater Lake, Oregon. ( I = 1000 organisms/10 minute horizontal tow)
