Modeling the trajectories of growth and reproduction in European Hake (Merluccius merluccius, L. 1758) from the Sea of Marmara, Turkey

Abstract

The study evaluated to model the growth and reproduction aspects of the hake, Merluccius merluccius, in the Sea of Marmara. On-board sampling was conducted on the commercial beam trawl fishery from February 2016 to January 2017. For the growth trajectories, using monthly length frequency data set, different methods were employed to improve parameter optimization. The variation of reproductive intensity was modelled using Generalized Additive Models (GAMs). The growth was fast and parameterized as L∞=65.9 cm, K=0.16 year-1 according to the Electronic Length Frequency Analysis (ELEFAN) with genetic algorithm optimization approach. Seasonal variation in growth, fitted a seasonally oscillating VBGF (soVBGF), indicated intense seasonality. The onset of the positive phase of the growth oscillation was observed around October proofed by a high fish condition that the growth starts accelerate after the summer period. A high gonadosomatic index (GSI) was evident over most of the year except between May and July, captured also the time component in the GAM modeling. The total length and fish condition have the highest impact on the GSI among the modeling parameters evaluated while temperature has low partial effect. The length at the first sexual maturity for females and males was calculated at 26.5 and 22.0 cm, respectively, lower than that of the Atlantic and Mediterranean waters. It is believed that this study allows deeper and new conclusions for the management of hake stock in the Sea of Marmara and Mediterranean Basin.