The trophic ecology of whiting (Merlangius merlangus) in the Irish Sea and its significance to the Manx herring stock

Abstract

Whiting ( Merlangius merlangus ) were trawled from a muddy sand trawling ground in the Irish Sea during 1981 and 1982. They had been feeding mainly on Norway pout ( Trisopierus esmarkii ), sprat ( Spratlus sprattus ), sandeels ( Ammodytes marinus ), herring ( Clupea harengus ), and cuttlefish ( Sepiola atlantica ). There was considerable seasonal variation in both the quantity and the type of food eaten. Yearly mean foodintake rate was estimated at 1·42, 3·35, and 7·25 grams fresh weight per day for one-, two-, and three-year-old fish respectively. Gross conversion efficiency during the second, third, and fourth years of life was calculated to be 0·14. Comparison with laboratory data suggeststhat whiting may use between 10 and 45 % of available metabolites for locomotion. Predation on herring seemed to be important, and may have accounted for 45 % of the variability in the numbers of recruits to the local stock.