Harvesting the mesopelagics - ecological and management implications

The main aim of HARMES was to increase the knowledge about mesopelagic organism abundance, diversity and ecological roles, thereby facilitating the management of a potential fishery and add to the overall management of the oceans. Several regions of the North Atlantic have been studied and major differences in physical structure, nutrient content, phytoplankton bloom dynamics have been revealed leading to phenological differences at higher trophic levels. Mesopelagic biomass and vertical distribution were very different among regions, probably related to epipelagic productivity and light regimes also governing active carbon vertical flux. Over the course of the project we concluded that abundance estimation of the mesopelagics was best done with submersed acoustics and echo-counting. The method has been published in peer reviewed journals. One uncertainty with the method is avoidance of the acoustic platform at depth, which we are now working to quantify. New developments of non-graded trawls have been used to improve abundance and biomass estimates of mesopelagic organisms and their size and weight. It is shown that the use of traditional pelagic trawls results in highly skewed size and weight distributions as well as biomass estimates. We have also been working with new optical methods to obtain vertical distributions from trawl samples. This has proven difficult due to organisms not being transported continuously to the back of the trawl, and we are still working on that. The model, NoBa Atlantis, was used to explore the combined effect of climate and fisheries. In these simulations, a harvest of the mesopelagic layer, both fish and zooplankton, were initiated using a fishing mortality at the maximum sustainable yield. The resulting mortality of mesopelagic fish might be on the lower side (F=0.15) and will be further investigated in future projects.

HARMES har bidratt til økt kunnskap om struktur og funksjon til det mesopelagiske økosystemet, blant annet ved utdannelse av en Post Doc og flere vitenskaplige publikasjoner. Det er stor interesse for mulig utnyttelse av mesopelagiske ressurser og kunnskap framkommet i HARMES vil kunne bidra til økt forståelse av hvilke ressurser dette kan være, hvordan de kan utnyttes og hvordan menneskelig adferd i forhold til mesopelagiske populasjoner best kan forvaltes. HARMES har særlig gitt økt kunnskap om diversitet, økologi og biomasser i det mesopelagiske systemet, samt nye metoder for hvordan biomasse og tallrikhet kan bestemmes.

The global population is expected to grow by several billion over the next few decades, leading to an increasing demand for marine protein and fat. Currently, the existing supply of marine raw materials cannot meet nutritional demand, neither directly supplied for human consumption, nor indirectly through aquaculture. Moreover, given the ambitions to expand Norwegian aquaculture of salmon by a factor of 3-5, finding new sources for feed becomes a matter of national strategic importance. Today, more than 95% of the global food production comes from agriculture. The mesopelagic zone, spanning from 200 to 1000 m depth, comprises about 60% of planet's surface and 20% of the ocean´s volume. The bulk of the global fish species live in this zone, by number as well as by biomass. It is furthermore a zone of wide diversity; the dominating taxonomic groups are crustaceans, various jellyfishes and cephalopods in addition to the fishes. The global marine fish biomass was estimated to be 0.899 billion tonnes in 2008, a number that is only slightly lower than the 1980 estimate of only mesopelagic fish biomass, ~ 1 billion tonnes. Recent studies indicate that the total amount of global mesopelagic biomass has been grossly underestimated. The latest assessment suggests a biomass in the order of 10 billion tonnes, roughly equivalent to 100 times the annual catch of traditional fisheries. The mesopelagic community may become the future source of marine protein and lipids that the aquaculture industry and global population need. Thus, there is a compelling rationale for a strong global effort into the exploration of mesopelagic organisms. While it gives Norway a unique opportunity, it also commands a responsibility to develop a sustainable management and harvesting regime. Our main aim is to increase the knowledge about mesopelagic organism abundance, diversity and ecological roles, facilitating the management of a potential fishery and add to the overall management of the ooceans.