The mesopelagic layer is a massive layer of biomass which stretches from 200-1000 meters depth in almost all locations of the world oceans. These layers are inhabited by many groups of animals, from small zooplankton to larger fishes. While studied since the 1960s, the mesopelagic layer has gained recent scientific and industrial interest due to its potentially large unexploited biomass. These layers are populated by small fishes, which may be ensonified and detected by echo sounders, creating a layer of reverberation called the deep scattering layer. In Norwegian waters, two of the most abundant mesopelagic fishes are the Glacier Lanternfish (Benthosema. Glaciale), and the Muellers pearlside (Maurolicus Muelleri). Recent estimates using echo sounders, suggest that their potential biomass could be as high as 10 billion tonnes worldwide. There are however several challenges with respect to quantifying mesopelagic fishes in an accurate manner. Unwanted swimbladder resonance, other animals with similar echoes, and fishes without or changing swimbladder may potentially create large biases in these investigations. Very low catchability in modern trawls may also complicate the measurements. In this study mesopelagic fishes were measured both with traditional survey methods using vessel mounted transducers, and a lowered acoustic probe where the fishes were measured at short range at their natural depths.

Google Scholar ->