21. These vertical migrations often occur over a large vertical distances, and are undertaken with the assistance of a swimbladder. 22. Thus, they perform a daily vertical migration of 15 meters, no small feat a creature only 3 mm long. 23. Nauplii and copepodids are positively phototactic and exhibit a daily vertical migration , rising during the day and sinking at night. 24. The swimbladders of deep sea fish are either absent or scarcely operational, and bathypelagic fish do not normally undertake vertical migrations . 25. Electronic tagging has shown Humboldt squid undergo diel vertical migrations , which bring them closer to the surface from dusk to dawn. 26. They follow vertical migrations of the zooplankton they feed on to the bottom during daytime and to the surface at night time. 27. Electronic tagging has shown that they also undergo diel vertical migrations which bring them closer to the surface from dusk to dawn. 28. This species undergoes vertical migration from 900 500 m depth during the day, rising to 263 102 m depth at night. 29. Most types of plankton and some types of nekton have exhibited some type of vertical migration , although it is not always diel. 30. In the North Sea, " P . pileus " makes large daily vertical migrations as do its main copepod prey.
