Large scale distrlbution of acoustical scattering layers at the Norwegian continental shelf and the Eastern Norwegian Sea

Abstract

Abstract Vertical and horizontal distributions offish and micronekton were mapped in a zigzag pattern from Lofoten, northern Norway to Stadt, southwestern Norway, in March 1992. Pearlsides (Maurolicus muelleri) were present whenever depth was sufficient for daytime requirements (i.e. > 150–200 m). They performed diel vertical migrations, characterized by ascent at dusk, followed by nocturnal descent, and a dawn ascent before downward migration to day depth. Nocturnal descent among pearls ide has previously been explained by preference for warm water to speed up digestion, but this could not explain the results in this study as relevant vertical temperature gradients were minor. A deep scattering layer consisting of mesopelagic fish, pelagic shrimps and other macroplankton was present outside the shelf. This layer was located beneath ca 300 m by day, while the tendency to carry out diel vertical migrations varied strongly between water masses. Blue whiting (Micromesistius poutassou) associated with the lay...