Fish distribution during nighttime, vertical beaming
Echoes from fish can now be seen in the open water and close to the surface. This is favorable conditions when acoustic data are being used for estimation of fish abundance. However, due to the small acoustic sampling volume close to the surface and the possibility that fish are avoiding the approaching survey boat, fish near the surface are not detected. A solution is to point the acoustic beam horizontally to the side of the boat. Fish close to the surface will be detected and added to the total abundance estimate.