Estimating reference points for unexploited fish stocks: A case study of two mesopelagic species

As the global demand for marine products rises, the sustainable exploitation of new marine resources is being explored. Robust tools are necessary to evaluate the sustainability of the potential exploitation of these resources due to the general lack of information about their catch history, population dynamics and resilience to exploitation. We adapted the s6 model, developed for the assessment of data-limited stocks, to estimate size-based natural mortality and Maximum Sustainable Yield (MSY) reference points F MSY and B MSY for unexploited stocks. We quantified the associated uncertainty as a function of the uncertain life-history parameters for unexploited stocks and evaluated the effect of alternative total stock biomass assumptions on the B MSY estimates. We demonstrate and discuss this model in a case study of two unexploited mesopelagic fish species, Benthosema glaciale and Maurolicus muelleri , in the Northeast Atlantic Ocean which are currently considered as potential fisheries resources. The results indicate that the s6 model is useful for the evaluation of unexploited resources, providing preliminary reference levels and their uncertainty with limited data requirements while simultaneously estimating natural mortality. For the two mesopelagic species, the results showed a median F MSY of 0.19 year −1 for B. glaciale and 0.11 year −1 for M. muelleri . B MSY estimates varied between biomass assumptions, with 95% quantiles of the Monte Carlo estimates ranging between 0.26-13.62 Mt for B. glaciale and 6.79-56.01 Mt for M. muelleri . A simulation study revealed that the high uncertainty of the estimates can be improved by obtaining better estimates of life-history parameters related to growth and recruitment and with increased sampling frequency of size frequency distributions. Following a precautionary approach to fisheries management, the large distribution of the reference point estimates should be carefully considered and function as motivation to expand research on the species before the commencement of a potential fishery.