Publication Abstract

Investigations on Sprattus sprattus population dynamics in the Bulgarian waters of the Black Sea, related to its trophic base and climate changes.

Investigations on Sprattus sprattus population dynamics in the Bulgarian waters of the Black Sea, related to its trophic base and climate changes.

Raykov VS Mihneva VV, G. M. Daskalov*

Sprat is one of the most commercially important fish species in the Black Sea. After a period of fishing mortality decrease in the early 1990s, due to complex factors such as reduced economics of the former socialist countries in parallel to mass occurrence of the competitive feeding ctenophore Mnemiopsis leidyi, since 2000 sprat fishery has been significantly intensified. Therefore, toward 1999 sprat stock biomass increase, however in the next five years the biomass and recruitment decrease again. For the period: 1996-2004 the condition factor and mean length of the sprat cohorts remain lower in comparison with the long-term averages, proving relatively poor physiological condition for the sprat populations. The condition factor and the asymptotic length depend significant negatively with copepods winter-spring biomass, and especially with Calanus euxinus and Pseudocalanus elongatus biomasses. The latter underlines a strong relationship existence between sprat population’s parameters and cold-water copepods abundance. Simultaneously, during the positive phase of the NAO winter index it has been observed an alternation in the copepods: cladocerans ratio, on the account of increased cladocerans share. As far as in the fourteen years period the sprat spawning biomass figure mostly negative correlation with the winter NAO index, we presume that climate factors might affect both - growth and the availability of appropriate prey for sprat.

Reference

Raykov VS Mihneva VV, G. M. Daskalov* (2007) Investigations on Sprattus sprattus population dynamics in the Bulgarian waters of the Black Sea, related to its trophic base and climate changes. Journal of Environmental Protection and Ecology, 8, (2): 319-331

Raykov VS Mihneva VV, G. M. Daskalov*

Journal of Environmental Protection and Ecology, 8, (2): 319-331