Mesopelagic fish composition and biomass

Several research institutes across the globe have become focused on the ocean’s mesopelagic zone, or “twilight” zone, which occurs between 200 and 1000 m. Scientists are studying the feasibility of fishing in the mesopelagic zone, since huge numbers of fish and other organisms inhabit these depths.

Mesopelagic fish may represent an untapped source of food and nutritional supplements for humans, and are used by some countries as fish meal for aquaculture. If resource extraction occurs, however, it is imperative that it be done sustainably. To determine the feasibility of sustainable fisheries in the mesopelagic zone, we must first determine the species composition of organisms present, as well as their biomass.

In the Northeast Pacific, our knowledge of mesopelagic fish diversity, distribution, and number is rudimentary. For example, most aggregations of organisms in the mesopelagic zone are dominated by small fish known as myctophids, but we do not know how many species are present, nor how they are distributed in space and time.

One of the primary goals of our twilight zone project is to characterize species composition, abundance and biomass of mesopelagic fish in populations off British Columbia, Canada. This region has a rich history of oceanographic exploration and data collection, yet little work on the mesopelagic zone has been conducted. Acoustic backscatter obtained with scientific echosounders aboard Canadian Coast Guard vessels will be used to identify the distribution and size of fish aggregations in the mesopelagic zone. Groundtruthing the acoustic data by trawling on acoustic marks is an essential part of this process and will allow us to estimate mesopelagic fish biomass in this region.