Baltic sprats boom when cod slip—and feed half a sea's web
True sprats are five oily Clupeidae species in genus Sprattus, though dozens of other small forage fishes wear the name. Packed with polyunsaturated fats, they are eaten worldwide, sometimes sold as sardines or even disguised historically as anchovy products.
Sprats are small, oily schooling fish that never stop swimming. Only five species in the genus Sprattus are true sprats, but FishBase lists 48 more fish whose common names end in sprat. Their constant activity gives them a far higher metabolic rate than larger relatives such as the Atlantic herring, and water temperature pushes it higher or lower. Eggs hatch about 15 days after fertilisation, and water density, temperature and depth all shape how many young survive.
The best-known population lives in the Baltic Sea, especially the Bornholm Basin in the south. There cod, herring and sprat are the key species: cod eat adult sprat, while sprat eat cod eggs and larvae. Sprat and herring compete for scarce zooplankton, migrating up and down the water column, but sprat are pickier. In autumn they favour the copepod Temora longicornis and the water flea Bosmina, in winter Pseudocalanus, and they mostly ignore tiny, quick Acartia, which also stay near the surface while sprat hold deeper by day.
Sprat survival fell in the late 1980s and early 1990s and then recovered, with spawning stock rising sharply, even as the Baltic grew less salty because fewer salty, oxygen-rich inflows arrived from the North Sea. Very cold winters remain a major threat to breeding success.
On the plate, northern Europeans smoke sprats and pack them in oil, which makes them one of the richest foods in purines. Their EPA and DHA levels match Atlantic salmon, up to seven times those of gilt-head bream, and some products sold as anchovies have long been made from sprats.
Source: Sprat
