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Ecologically and economically sustainable mesopelagic fisheries

Periodic Reporting for period 2 - MEESO (Ecologically and economically sustainable mesopelagic fisheries)

Reporting period: 2021-03-01 to 2022-08-31

MEESO’s overall goal is to quantify the spatio-temporal distributions of biomass, production and ecosystem role of mesopelagic resources and to assess sustainable management options for their exploitation. To achieve this, MEESO will establish new knowledge and data on the mesopelagic community, its biodiversity, drivers of its biomass, its role in carbon sequestration, and its interactions with the overlying epipelagic communities which include important commercial fish stocks. MEESO will develop and implement new acoustic and trawling technologies needed for obtaining data from this remote and poorly understood marine ecosystem zone. MEESO will also evaluate the potential for mesopelagic biomass for sustainable products included in the human food chain. Combining, for the first time, leading experts in science, engineering, fisheries and governance, MEESO will develop commercial fishing and processing technologies and mapping of contaminant and nutrient contents to explore the basis for a viable fishery and creation of jobs. The new tools and technologies, as well as assessment and management roadmaps, developed in MEESO will establish the trade-offs between exploitation, sustainability and viability of the resource, and identify options for its governance.
A major objective of MEESO is to improve the quantification of mesopelagic resources. Acoustic and optical instruments have been developed and deployed to mesopelagic depths to enable observations of individual organisms rather than only populations or aggregations. These, used with theoretical acoustic scattering models, have significantly advanced the methods for studying mesopelagic organisms. Improvements in catch equipment and instrumentation have made direct biomass estimation possible.
Since the net herding efficiency for small mesopelagic fish species is unknown, commercial trawls targeting these species need to consider the potential net panel selectivity along the entire trawl body. We have addressed this problem using laboratory experiments with mesopelagic fish together with a simulation model that helps to predict the potential net panel selectivity.

As part of the commercial development of products made from mesopelagic fish, several bioactivities have been revealed and are being investigated further. Food safety issues have been uncovered (fluoride, wax esters, long-chain monounsaturated fatty acids, trace elements, dioxins and furans), and the work to define suitable categories of use is ongoing.

MEESO has collated data from all major areas of the North Atlantic. Regional maps of abundance and biomass have been assembled in several study sites across the North Atlantic based on acoustics and trawl samples. Analysis of historical data shows that among four sub-polar basins in the North Atlantic the biomass of mesopelagic micronekton was higher in the western areas and peaked in the Irminger Sea. Vital rates of two key species, Mueller´s pearlside and glacier lanternfish, have been analysed and growth rates, sex ratio, maturity, and fecundity by area are established. The passive flux of carbon (marine snow) is being estimated and combined with data on daily vertical migrations of the mesopelagic fauna (active carbon flux) to assess their relative roles, and that of the mesopelagic generally, in carbon sequestration.
A suite of models is being applied to estimate mesopelagic stocks and their resilience to harvesting and environmental change. In order to have parameterisation and validation data for the models we have reviewed information on key demographic parameters of the two key species from published literature and our new results. A method for analysing length-frequency data has been used to produce new growth, mortality, and yield per recruit estimates for Mueller´s pearlside and glacier lanternfish. Results from a spatial population model for glacier lanternfish suggests stock decline, without fishing, as a result of projected ocean warming. Runs of an end-to-end ecosystem model with a new glacier lanternfish module show large variations in biomass and growth rates in space and time and suggest that the extent of vertical movement has a large impact on the dynamics. A global model simulating lower and mid-trophic functional groups has been implemented in two new configurations to include our two key mesopelagic species.

MEESO aims to assess the varied economic, biological, and societal risks associated with mesopelagic fishing, including its potential economic impact, and factors determining social acceptance. Our findings so far suggest that a mesopelagic fishery is possibly commercially viable provided that catch rates are similar to current fisheries, solutions are found to address onboard deterioration of the catch, and that the biological limits are strongly protected. The public costs associated with the impact on oceanic carbon sequestration, however, may exceed the private net benefits to industry and consumers. Compared to the size of the global market for reduction fish, fishmeal, and fish oil the contribution of a mesopelagic fishery by the EU member states considered (Denmark, Spain, Ireland) will be relatively small (of the order of 1% of global output). Interviews with key governance stakeholders and analyses of a collection of over 2700 policy documents have shown that area-based management tools and international ecosystem based environmental impact assessment under negotiation within the BBNJ (Biodiversity Beyond National Jurisdiction) treaty are among the most promising options going forward, and we are using these results to inform our WP7 modelling.
To achieve its main goal MEESO will rely on technology and methods that are state-of-the-art, and beyond, in five themes: Technology, Knowledge acquisition, Management, Governance and Capacity building. We are setting new standards for measuring and quantifying mesopelagic resources by deploying submersed wideband echosounders, enabling direct enumeration of individual mesopelagic organisms and their biomass in combination with theoretical scattering models. The development and deployment of larger, fine-meshed trawls for scientific surveys, as well as better methods and technology for trawl monitoring has enabled the project to move beyond some of the largest sources of uncertainty in current trawl based methods for mesopelagic resource mapping. We have also progressed the on-board and on-land processing of mesopelagic biomass.

We have produced the most extensive review of published estimates of growth rates, natural mortality, asymptotic size, maturity, and length-weight relationships of Mueller´s pearlside and glacier lanternfish from different geographical locations. Our analysis of these data has revealed very high natural mortality rate estimates. Our suite of novel population and ecosystem models is now functional and ready for use in assessment of harvest strategy and climate change scenarios. The bioeconomic models developed will enable researchers to evaluate sustainable management strategies for the mesopelagic zone, and to quantify the various trade-offs. The cost-benefit analysis for mesopelagic fishing demonstrates how such trade-offs can be analysed in a way that is simple yet insightful. Our ongoing analyses are expected to highlight the potential value of carbon services of the mesopelagic under main area-based management scenarios that were identified during policy analyses.
Echoes from resolvable individual organisms at 800 m depth

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