Food consumption by clupeids in the Central Baltic: evidence for top-down control?

Abstract

Considerable changes have taken place in the pelagic ecosystem of the Central Baltic Sea during the last decade. Owing to a combination of high fishing pressure and unfavourable hydrographic conditions, the cod (Gadus morhua) stock as the top predator in the system was reduced from a high level in the early 1980s to its lowest size on record in the early 1990s. The preferred prey species sprat (Sprattus sprattus) showed a significant increase in population size since the late 1980s to the highest level on record in recent years, while the herring (Clupea harengus), another important planktivore in the system, did not show such a response. We investigate whether fluctuations in clupeid stock size cascade down to the trophic level of mesozooplankton, based on stomach content data and daily ration estimates in combination with stock sizes estimated from Multispecies Virtual Population Analysis. Estimates of daily consumption by the populations of the two species for 1978–1990 were compared with standing stocks of mesozooplankton species. No evidence was found for food limitation as might be expected if clupeids exert a strong top-down control on mesozooplankton. Also no influence on interannual variability of mesozooplankton abundance was detected. However, predation did contribute to the seasonal development of two copepod species (Pseudocalanus elongatus and Temora longicornis).

Planktonic production and carbon transfer efficiency along a north–south gradient in the Baltic Sea

“…However, top-down effects are very likely to affect the observed pattern since planktivorous fish reduce zooplankton biomass (Möllmann & Köster 1999). Herring and sprat, which are both planktivores, are the dominant fish species in the Gulf of Bothnia, whereas herring, sprat and cod (a piscivore) dominate in the Baltic proper (ICES 2007).…”

Diet composition and food selectivity of sprat (Sprattus sprattus) in Hardangerfjord, Norway

“…Sprat is an ecologically important pelagic fish species, acting as a link between plankton and production on higher trophic levels. Sprat feed on zooplankton (Mö llmann et al 2004;Ellis & Nash 1997), and have the ability to control their food sources through selective feeding (Arrhenius 1996;Mö llmann & Kö ster 1999). Sprat is also important as prey for top predators, e.g.…”

Baltic sprat larvae: coupling food availability, larval condition and survival

“…Baltic sprat is of high ecological importance (Rudstam et al 1994, Kornilovs et al 2001 both as an important prey for top predators (e.g. cod, harbour porpoise) and as a major predator on zooplankton and fish eggs (Arrhenius & Hansson 1993, Bagge et al 1994, Köster & Schnack 1994, Möllmann & Köster 1999, Köster & Möllmann 2000a. It is also presently the most abundant, commercially exploited species in the Baltic Sea (ICES 2004), and its management is challenged by large stock fluctuations mainly caused by a highly variable recruitment success.…”