Fig. 3.

Monthly average echograms from the 38-kHz echo sounder (covering 24 h) illustrating the deeper part of the water column (~200–390 m) in summer (represented by August 2008), autumn (represented by September 2007), winter (represented by January 2008), and spring (represented by May 2008). Arrows in echograms indicate the different behavioral patterns; No diel vertical migration (NoDVM), inverse diel vertical migration (IDVM), and normal diel vertical migration (NDVM). The color scale refers to average volume backscattering (S _v) for each month; dark red illustrates the strongest, and white the weakest backscatter. Black and white bars above echograms depict night and day separated by times for sunrise and sunset for the 15th each month. Time is given as UTC (local standard time −1 h)