Underwater optics and behavioral responses of krill to presence of fish predators affect fish-plankton interactions
Original version
This report is not to be cited without prior reference to the authorsAbstract
In clear oceanic waters off the Norwegian shelf and in outer shelf waters,
mesopelagic fish (Maurolicus muelleri) were located at approximately 200 m
by day. Across a front into water of lower light penetration, M. muelleri
ascended about 100 m. Concurrently, a layer of krill (Thysanoessa inermis)
appeared at between 150-200 m, i.e. below their potential predator M.
muelleri and generally about 100 m above the bottom. The bottom
associated fish Norway pout (Trisopterus esmarkii), occasionally ascended
from the benthic boundary layer, foraging in the lower part of the krill
layer. However, evidence was found that T. inermis responded to their
presence by upward swimming. These results indicate that optical
properties of water masses may be prominent in governing plankton and
fish distributions and their predator-prey interactions. They furthermore
suggest instantaneous behavioral responses in fish and krill to the presence
of their respective prey and predator.