Seasonal variations in the energy density of fishes in the North Sea

The energy density (E-D, kJ g(-1) wet mass) of saithe Pollachius virens, haddock Meleanogrammus aeglefinus, whiting Merlangius merlangus, Norway pout Trisopterus esmarki, herring Clupea harengus, sprat Sprattus sprattus, sandeel Ammodytes marinus and pearlsides Maurolicus Muelleri, from the North Sea, increased with total length, L-T. However, there was not always a significant (P >0(.)05) linear relationship between L-T and E-D. Seasonal differences in E-D were obvious in mature fish, while geographical differences were insignificant. For all species there was a highly significant correlation (P <0(.)0001) between the percent dry mass of the fish (D-S) and E-D. A general relationship was established for gadoids and sandeel E-D = -3(.)1492+0(.)3459 D-S and herring E-D = -4(.)6395+0(.)4170 D-S. Thus seasonal and size-specific data on E-D needed for bioenergetics and gastric evacuation models can be determined simply from D-S, which is considerably less costly and time consuming than calorimetry or proximate analysis. (C) 2001 The Fisheries Society of the British Isles.