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Topic: Deep-sea creatures: Mesopelagic resources

Fish and other animals that live at depths of 200-1,000 metres are referred to as mesopelagic. The world’s oceans are probably home to more than ten billion tonnes of these species.

All oceans have a mesopelagic zone, but they vary in their abundance of fish. Calculations of the quantity of mesopelagic fish and other organisms in the oceans fluctuate. Previously it was estimated that the oceans contained around one billion tonnes of these resources in total. More recent studies have called that number into question. There is now strong evidence that the estimate needs to be increased significantly – probably to at least 10 billion tonnes.

The term “mesopelagic organisms” covers a number of fish, including the glacier lantern fish and Mueller’s pearlside, as well as a wide range of invertebrates. The invertebrates include octopus and other molluscs, jellyfish and planktonic crustaceans such as prawns and krill.

In addition, various species that are already harvested are categorised as mesopelagic species. These include the beaked redfish, European hake and various shellfish such as the northern prawn.

Gaps in our knowledge

Mesopelagic fish and other animals are small, fragile and decompose quickly. It is therefore challenging to perform research into these species. They live far out to sea and deep down in dark waters. This makes it impossible to monitor them through ordinary research missions and catch data. Dedicated surveys covering much larger areas are required, as well as specialist sampling equipment.

We know quite a bit about mesopelagic communities, but there are also many gaps in our knowledge. Moreover, to date no-one has successfully harvested mesopelagic fish commercially on a large scale, although trials have been carried out in countries like Iceland and South Africa, as well as Norway.

Mesopelagic species are an area of focus for the IMR

The Institute of Marine Research (IMR) has mesopelagic resources as one of its areas of focus. We are doing research to learn more about the diversity of the mesopelagic animal community and the roles of the various species in marine ecosystems.

This information is important for assessing the impacts of harvesting on marine ecosystems and working out the quantities of these resources that can be harvested in different areas. In order to establish fisheries, we must also discover the where the largest concentrations of the relevant species are found and develop suitable fishing and processing technology. This must be done gradually, initially through trial fishing, followed by gradual expansion within a sound, sustainable framework.

Mesopelagic fish for dinner?

Traditionally, mesopelagic fish have not been considered suitable for human consumption. However, there is a big and growing demand for marine fat and protein as a raw ingredient for food production and for the feed given to farmed species like salmon and trout.