MEPS prepress abstract  -  doi: 10.3354/meps07364

ABSTRACT: Mesopelagic acoustic scattering layers (SLs) were studied from a stationary research vessel in two fjords. Diel vertical movements of SLs were assessed by hull mounted transducers, while in situ behavior of individuals constituting the SLs was resolved by a submerged echo sounder. The study focused on SLs made up of the lightfish Mauroliucs muelleri and the lanternfish Benthosema glaciale. Individual fish migrated in a pronounced step-wise manner, alternating between vertical movements and stationary phases both during ascent and descent. Mean lengths of steps varied between 2.01m and 0.40 m, and mean duration of stationary phases between 69 s and 36 s for fish in different SLs. Such travel-pause behavior concords with saltatory search, where the fish scan the water for prey during the stationary phases, relocate and scan a new water parcel. Little activity was recorded among individuals in deep water, apart from infrequent, short shifts in vertical distribution. This study shows that stationary submerged echosounders can provide detailed information on in situ behavior of mesopelagic fish.