Sprat feeding behaviour, selective predation, and impact on plaice egg mortality

Although the causes of fish egg and larval mortality are poorly understood, predation is thought to be a major contributing factor. The feeding behaviour of sprat at a plaice spawning ground in the Irish Sea during February 2009 is described and their contribution to plaice egg mortality investigated. Acoustic observations and analysis of stomach contents revealed diel behaviour, with dense schools associated with feeding formed during daylight dispersing into thinly spread aggregations at dusk. Of 338 stomachs analysed, 95 contained identifiable prey items. Feeding activity peaked between 10:00 and 18:00, for all food groups. Numerically, gadoid eggs were the most frequently consumed prey (64), followed by copepods (25) and plaice eggs (7). Plaice eggs were present in 91 of the stomachs analysed. Converting stomach content data to daily consumption suggested that sprat may consume 73 of all plaice eggs spawned in the area. Predation by sprat appears to account for a large proportion of plaice egg mortality, so the abundance and distribution of this pelagic predator may have important consequences for the recruitment dynamics of other fish species. Moreover, fish eggs may be an important energy source for sprat during late winter, when alternative prey is scarce. Crown copyright