Mesopelagic organisms are important prey for many commercially valuable species (e.g. tuna, swordfish, squid) and charismatic megafauna (e.g. marine mammals, seabirds, pelagic sharks). Many of these top predators dive into the mesopelagic zone to feed on deep-sea fishes and squids, while others exploit the diel vertical migration of mesopelagic organisms to surface waters at night.

Commercial fishing of mesopelagics may change the composition, biomass and interactions within the pelagic community and affect the transfer of energy from lower to higher trophic levels. However, there are still huge gaps in our understanding of the mesopelagic predator-prey network making it difficult to predict effects of exploitation on top predators or entire food webs.

The IMAR team is analyzing the behavior and vertical movements of cetaceans, sharks and tunas instrumented with multi-sensor tags with respect to mesopelagic distribution and biomass to quantify interactions of top predators with mesopelagic prey. In addition, analyses of stable isotopes and molecular markers, together with information on prey nutritional quality, is being used to determine the diet, energy requirements and mesopelagic consumption by these predators.

We hope this work will contribute to addressing some of the main questions of SUMMER:

  • Who are the key mesopelagic species and interactions controlling the trophic flow from the deep sea to epipelagic layers and across trophic levels?
  • What could be the consequences for epipelagic and deep top predators of fishing mesopelagic organisms?
  • How could this affect the ecosystem services provided by these predators (e.g. fisheries, ecotourism)?

Text by: Mónica Silva, IMAR