Catching mesopelagic fish may have climate consequences

To shed light on this dark and cold area of ​​the oceans, the research team has developed different action protocols since 2019 to estimate the total biomass of this region, establish its role and importance in the food chain, and analyze its role. in carbon transfer and sequestration.

Research has shown that mesopelagic fish have day-night migratory behavior, rising to surface waters at night to feed, and descending to safer depths during the day to avoid predators. This migration is essential not only for their survival, but also for the functioning of the ecosystem, as it contributes to the transfer of carbon and nutrients to the lower layers of the ocean.

«The main conclusion we have obtained is that, today, it is more beneficial to protect this area than to exploit it. It provides essential nutrient and climate regulation services, and sustains numerous fish populations of commercial interest,” highlights Raúl Prellezo, AZTI fisheries economics expert and project coordinator.

Abundance and molecular sources

The research, led by the AZTI technology center, has estimated an abundant biomass in this area: 1,300 million tons, which represents 87% of the total pelagic biomass and is 15 times higher than all oceanic fishing in 2022 (81 million tons).

«Despite this large biomass, the commercial viability of exploiting this area for fishing is limited. First, due to the wide and dispersed distribution of the fish. Second, due to its small size, which requires processing into fish meal and oil, Third, due to its slow metabolism and low productivity. All this makes them very vulnerable to overfishing,” explains Prellezo.

The study has also looked at how extreme conditions at these depths have driven the evolution of microbial communities with unique biochemical traits and promising sources of novel molecules.

The SUMMER project has evaluated the antimicrobial activity of around 700 microbial extracts against various human and fish pathogens, as well as against human cancer cells. The results highlight the potential of mesopelagic organisms for pharmaceutical applications.

Likewise, bacteria that produce omega-3 fatty acids have been found in fish viscera, which are important for the nutraceutical industry and aquaculture.

“Profitability issues in sourcing fish oil require careful evaluation to determine whether it is commercially viable. However, the selective search for organisms in the mesopelagic zone offers a promising and sustainable way to take advantage of microbial and chemical diversity in possible pharmaceutical and nutraceutical advances,” adds the AZTI researcher.

Fundamental ecological role

The research results especially highlight the fundamental ecological role of mesopelagic organisms in carbon transport and food webs, underlining the important social risks of overfishing.

The nocturnal movement of mesopelagic organisms, including fish and zooplankton, to surface waters to feed is the largest daily migration by biomass on the planet. According to the study, 44% of the biomass in this area makes these vertical migrations. This active flow, as the report highlights, represents 1.5 times all CO2 emissions from automobiles worldwide.

To support the management of the exploitation of mesopelagic organisms, the project has developed a virtual tool that allows stakeholders to interactively experience the impacts of diurnal vertical migrations on the biological carbon pump.

The research team has also quantified the dependence of predators on certain mesopelagic resources and has observed that all top predators depend to a greater or lesser extent on these resources, which is why food webs are especially sensitive to the capture of mesopelagic fish.

The SUMMER initiative, supported by funding from the European Union’s H2020 program, brings together a consortium of 22 institutions led by the AZTI technology center. This project is distinguished by its transversal and multidisciplinary approach, integrating research personnel from various areas such as economics, genetics, microbiology, food and ecosystems. This collaboration allows a comprehensive analysis of mesopelagic resources, ranging from the evaluation of their economic viability to the study of the bacteria that inhabit these organisms and their potential application in aquaculture. In addition, the initiative has had the participation of industrial companies that are interested in exploring the potential of these mesopelagic resources from multiple perspectives.