Viability of a mesopelagic fishery in the Bay of Biscay 3

A recently estimated high mesopelagic biomass level, along with the increasing demand for raw material for fish oil and fishmeal, has sparked interest on exploiting mesopelagic populations. However, their exploitation is controversial due to their ecological role as primary prey for other populations and as CO2 sequestrators. Therefore, before starting a new fishery, the three pillars of sustainability, ecological, economic and social, should be assessed. In the Bay of Biscay Maurolicus muelleri is the main mesopelagic species. Based on data collected over an eight-year period, a simulation model was implemented to assess the biological, economic and social performance of different fleets and exploitation levels. The conditioning of the population dynamics model presented several challenges, as the available survey index did not cover the full population distribution every year and the population had never been exploited in the Bay of Biscay. To overcome these problems an absolute population index was estimated using a spatio-temporal model, which was later used to adjust an age structured population dynamics model. Both models were fitted using Bayesian statistics to account for inherent uncertainty. The fishery was conditioned by identifying the most suitable fleet and estimating the initial investment and operational costs. The social pillar was approached through the social cost of carbon. The estimated biomass of M. muelleri in the Bay of Biscay fluctuated around 1.2 million tonnes. When it comes to exploitation, an industrial fishery may generate profits while maintaining a sustainable biomass level under good efficiency conditions. However, it would be challenging to recover the initial investment. Additionally, the estimated added value generated by this fishery would not be able to compensate for public costs associated with the impacts on carbon sequestration.