First maturity size of the Black Sea anchovy and its implications on the age-based stock assessment models

Abstract

This study aims to estimate the Black Sea anchovy's first maturity length and its relationship with the ambient temperature to investigate possible consequences of global warming on the stock. The study also evaluated how changes in maturity size/age affect the stock assessment model and scientific advice given by the Scientific, Technical, and Economic Committee for Fisheries (STECF), an advisory board of the European Commission, for the sustainable exploitation of the stock. A total of 7218 anchovies sampled during the scientific surveys conducted in 2013, 2014, 2015, 2018, and 2020 covering the southern Black Sea suggested that the L₅₀ of the species was 7.6 ±0.07 cm in TL. On average, 30% of the anchovy were found to be matured at age zero, representing 8% of the population. It was also noted that the zero-age-maturity rate was the highest during the warmest year. When the XSA model, which was chosen by the STECF in 2017 to assess the status of the stock was re-run with the newly estimated parameters, the Spawning Stock Biomass was estimated to be 1.5 times higher than the value used to produce scientific management advice. While maturity information significantly affects the stock representation of the model in the short run; in the long run, the management policies produced with these results may cause the stock to be mismanaged. Thus, the results must be considered to enhance the quality of the scientific advice given to manage the Black Sea anchovy stock.