Energy allocation in Atlantic cod (Gadus morhua) from different feeding grounds along a North-South gradient in the Central North Sea
Macharia, K.B. (2013). Energy allocation in Atlantic cod (Gadus morhua) from different feeding grounds along a North-South gradient in the Central North Sea. MSc Thesis. VUB/Universiteit Gent/Universiteit Antwerpen: Brussel, Gent, Antwerpen. 14, 40 pp.
Feeding grounds of high quality increases individual condition which positively influences population growth rate, survival and bolsters reproductive capacity of fish. To determine energy accumulation at different feeding areas, which in turn influences individual conditions, we compared prey items consumed, condition indices and energetics in Atlantic cod (Gadus morhua) along a North-South gradient in the Central North Sea. Pandalus montagui and Crangon crangon were the most important crustaceans whereas among the fish, Callionymus lyra and Merlangius merlangus formed an integral part of Atlantic cod’s diet. Crustaceans formed an important food source for one-year old Atlantic cod while larger Atlantic cod (>2 years) consuming mainly larger fish. The main source of energy to the Atlantic cod is lipids. Liver stores 99 % of the total lipid content whereas white muscles hold 1 %. Protein is the second important source of energy which solely contributes 86 % of the total energy available in the muscle. Carbohydrates contribute the least amount of energy which is significantly reserved in the liver. Liver holds 91 % of total energy available (kJ/g) in Atlantic cod whereas the white muscle holds 9 %. Total energy available (kJ/g) increased with age. Gonado-somatic index (GSI), Fulton’s condition factor (K) and Liver-somatic index (LSI) increased with age. This could be attributed to the diet consumed. Fulton’s condition factor was relatively stable indicating that Atlantic cod were feeding to satiation in their respective feeding grounds. GSI increased with age due to large allocation of energy to gonad maturation as the Atlantic cod matures in preparation for spawning. LSI increased with age presumably due to the consumption of a high proportion of lipid-rich fish prey by large Atlantic cod. Latitudinally, there was a uniform distribution of crustacean and fish prey items. Pandalus montagui and Crangon crangon were the most important crustaceans distributed at high latitude positions towards the coastline of England and Denmark, respectively. Crangon crangon occupied the lower latitude position. Pisces species were evenly distributed. Pleuronectidae, Gobiidae and Clupeidae were distributed towards the coastline of Germany and Denmark whereas Clupeidae, Agonidae and Gadidae were distributed towards the England coastline. There was no clear trend for total energy available (kJ/g) and condition indices along the latitudinal gradient though a subtle increase for total energy available (kJ/g) and gonado-somatic index towards the north was observed.
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