WP 4: Case study – Black Sea sprat

Lead: National Institute for Marine Research and Development, Romania 

Sprat (Sprattus sprattus) is one of the most abundant and commercially important pelagic fish species in the Black Sea, and it is an important prey for larger fishes. It is distributed over the whole Black Sea, but it is most abundant in the northwestern region and shelf waters.

Sprat reaches maturity at one year and reproduces during the whole year, but its peak spawning is between November and March. The recruitment is strongly controlled by winter hydroclimatic conditions and plankton blooms.

In spring, schools migrate to coastal waters for feeding. During summer, the juvenile and adult sprat populations leave the upper warm layer and thus avoid severe competition for food with other plankton-consumers including Mnemiopsis leidyi. During this period their preferred food consists mainly of the cold-water Calanus and Pseudocalanus copepods living below the cold intermediate layer of the water column.

The reduction of the sprat stock in the early 1990s was partly due to food competition with the Mnemiopsis population outburst. As with the other commercial stocks, heavy overfishing took place before and during the M. leidyi outbreak as well, which aggravated the stock depletion. In addition to M. leidyi, the jellyfish Aurelia aurita distributed in deeper waters has a strong trophic interference with sprat. This may explain the coincidence between the declining phase of sprat recruitment and biomass and the peak abundance of A. aurita during the 1980s. Sprat has been subject to both artisanal and commercial mid-water trawl fisheries since at least the early 20th century; catch data (often monthly) are available since that time.

Size and age compositions have been regularly assessed (monthly) based on samples from the commercial landings or research surveys. CPUE has been monitored for different vessel type, fleets, and gear since the 1980s, and fat content has been measured since the 1960s. The recent assessment is considered sufficiently reliable for forecasts, and its outputs have been used for short-term forecasts.

Analyses in this workpackage​ will focus mostly on interactions of climate-zooplankton with recruitment and adult growth and condition; some limited sampling of sprat and zooplankton will be conducted to continue ongoing time series and for validating lower-trophic level oceanographic models.