Conserve immatures and rebound the potential: stock status and reproduction of whiting (Merlangius merlangus [Linnaeus, 1758]) in the Western Black Sea

ABSTRACT

The stock structure and productivity components (growth, maturity and mortality) of the Black Sea whiting Merlangius merlangus were studied in the western Black Sea for a year. The results aim to improve fisheries management of whiting in the Black Sea. Fresh samples were collected from commercial bottom trawlers between October 2017 and September 2018. Using monthly length-frequency data set for the growth trajectories, a bootstrapped procedure was employed to improve parameter optimization. Duration and timing of the spawning season and size at sexual maturity were modelled using generalized additive models (GAMs). The presence of clear differences in oocyte size groups indicates that oocyte development of Black Sea whiting is a ‘group synchronous’ ovarian developmental process characterized by continuous reproduction. From the gonadosomatic index values, their spawning activity intensifies especially between October and April, captured also in the time component in the GAM modelling. The length at first maturity was 13.9 cm for females and 12.5 cm for males. The mortality rates, yield per recruit analyses, and length-based indicators suggest that whiting is heavily exploited with alarming signs of overexploitation. Undoubtedly, setting catch limits and re-establishing management plans will be the first two steps to ensure reproductive success and prevent overfishing (F > Fmsy).

KEYWORDS:

• Stock status
• whiting
• spawning cycle
• length at first maturity
• Black Sea

Acknowledgements

This work was supported by Istanbul University BAP Scientific Research Projects Coordination Unit. Project number: FAB-2017-24719. We thank Dr Aylin Ulman from Mersea Marine Conservation Consulting for helping us with English editing and Dr Nazli Demirel for valuable comments and suggestions. The authors also thank Prof. Dr Meriç Albay for helping in the summer sampling period.

Disclosure statement

No potential conflict of interest was reported by the authors.