Spatial and temporal variation in the distribution and abundance of pelagic fish eggs and larvae off Giresun, south-eastern Black Sea, Turkey

Abstract

Background. Giresun Bay is an important spawning ground of many migratory fish species and hence it has been a major fishing area of pelagic fishes in the Turkish territorial waters of the Black Sea. However, this area has not been evaluated thoroughly for the abundance and distribution of pelagic fish eggs and larvae, which are prerequisite for understanding the dynamics of fluctuating fish populations. The presently-reported study aimed to fill this gap in the existing knowledge of spatial and temporal variation in the distribution and abundance of ichthyoplankton in the south-eastern Black Sea. Materials and methods. Bimonthly surveys were carried out from January through November 2009 at inshore and offshore sites (>38°E, >40°N). The samples were collected by horizontal tows with Manta nets. The mouth of the net was equipped with flowmeters to measure the amount of water passing through the net during each tow. Results. The horizontal tows returned a total of 13 556 eggs and 1304 larvae representing 26 species (from 22 families): Engraulis encrasicolus, Sprattus sprattus, Merlangius merlangus, Gaidropsarus mediterraneus, Atherina boyeri, Scorpaena porcus, Chelidonichthys lucerna, Dicentrarchus labrax, Trachurus mediterraneus, Diplodus annularis, Sciaena umbra, Mullus barbatus, Gymnammodytes cicerelus, Ctenolabrus rupestris, Symphodus ocellatus, Trachinus draco, Uranoscopus scaber, Parablennius sanguinolentus, Parablennius tentacularis, Blennius sp., Ophidion rochei, Callionymus pusillus, Gobius sp., Arnoglossus kessleri, Buglossidium luteum, Pegusa lascaris. Overall, the dominant species were E. encrasicolus with 89.8% of all collected eggs, followed by G. mediterraneus (7.0%). Similarly, 47.4% of the total larvae were represented by E. encrasicolus, followed by P. sanguinolentus (22.8%) and S. sprattus (13.2%). The colder months (January, March, and November) presented a total of four species: S. sprattus, B. luteum, Gymnammodytes cicerelus, and Gaidropsarus mediterraneus. The warmer months had a greater variety of different species than colder months. Of these, E. encrasicolus was the most dominant species, providing the maximum abundance of fish eggs and larvae in September. The abundance of E. encrasicolus eggs and larvae decreased from offshore toward inshore sites highlighting the preference of this species to deeper waters for spawning as well as for nursery purposes in Giresun Bay. Conclusion. The results of this study suggest that the length of the closed fishing season in the Black Sea should be reconsidered. We suggest that it should be extended to include also the last week of September in order to provide more time for pelagic fish (e.g., E. encrasicolus) to complete their spawning period. This could result in a healthier and more sustainable stock of E. encrasicolus in the Black Sea.