Fisheries Reference Points under Varying Stock Productivity and Discounting : European Anchovy as a Case Study

Funding Information: This work was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 675997. The authors are very thankful to Prof. Dr. Mehmet Aydın from the Ordu University Fatsa Faculty of Marine Sciences for his support and contribution and to anchovy fishermen who answered our questions sincerely and patiently. We would also like to thank constructive comments received by anonymous reviewers during the peer review. Funding Information: This work was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 675997. The authors are very thankful to Prof. Dr. Mehmet Aydın from the Ordu University Fatsa Faculty of Marine Sciences for his support and contribution and to anchovy fishermen who answered our questions sincerely and patiently. We would also like to thank constructive comments received by anonymous reviewers during the peer review. Data Availability Statement: The data that is used and support the findings are publicly available. Catch and price statistics of the anchovy are openly available by the Turkish Central Statistical Database via the link: https:// biruni.tuik.gov.tr/medas/?kn=97&locale=tr. Biological parameters of the anchovy stock assessment are available in the report STECF-14-14, EUR 26896 via . Economic survey data of the anchovy fishing fleet can be made available upon request. Publisher Copyright: © 2022, Mediterranean Marine Science. All Rights Reserved.European anchovy (Engraulis encrasicolus) is the main commercially exploited fish stock in the Black Sea region, providing a vital source of livelihood and revenue for local communities and national economies. In recent decades, the Black Sea anchovy stock has faced many human-induced threats, including overfishing, eutrophication, invasive species, and climate change while these threats have raised concerns about the status and long-term productivity of the stock. To ensure sustainable levels of exploitation under potential future changes in stock productivity, we here estimate and compare a suite of biological and economic reference points under different levels of stock productivity and discount rates using an age-structured bioeconomic model setup. Our model simulations showed that optimal fishing mortalities achieving maximum sustainable yield (FMSY) and maximum economic yield (FMEY) increase at higher stock productivity but are always lower than the historically high mean levels of exploitation. Furthermore, we illustrate that the stock biomass at maximum economic yield (BMEY) is larger than the stock biomass at maximum sustainable yield (BMSY) at all stock productivities and discount rates, except at low stock productivity under high levels of discounting (i.e., 10%, 20%). By illustrating the ecological and economic benefits of reducing exploitation rates, we expect that our estimated reference points can add value to the decision-making process for the management of the European anchovy fishery and ensure long-term sustainable management even under future climate-driven changes in stock productivity.Peer reviewe

Trophic impact of Atlantic bluefin tuna migrations in the North Sea

AbstractLarge highly migratory predators can have major impacts on local marine ecosystems by reducing prey populations and leading to trophic cascades that affect the entire fish community. These trophic interactions are typically non-linear and can alter both the migratory behaviour of the predator and the stability of the fish community. The impact of a migrating top-predator is investigated here for Atlantic bluefin tuna in the North Sea. Bluefin tuna has been absent from the region for half-century, but recent years have seen recovery of migrations and a return of bluefin tuna in the area. We use a size spectrum model to analyse the trophic impact of the returning tuna on the entire fish community, under scenarios with varying levels of tuna consumption and fishing mortality on the prey. We show that with high level of prey fishing mortality in the North Sea, the effect of a tuna re-colonization results in only limited trophic cascades. However, high tuna consumption or changes in fishing mortality may result in a sudden recruitment failure of small-pelagic fish due to cascading effects on the fish community. In present-day conditions, the level of tuna consumption that triggers recruitment failure is lower at increasing fishing mortalities on their prey, providing indications for the future sustainable management of both small-pelagics and bluefin tuna in the area.</jats:p