Comparative feeding ecology of roundnose grenadier (Coryphaenoides rupestris) in Norwegian fjords
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In the ocean, energy is transferred from the productive primary producers at the surface, down to the demersal fish fauna at the sea floor. When moving away from the surface layer, there is a decline in food availability, and demersal fish species has evolved different feeding strategies due to this (Merrett and Haedrich, 1997). Even though many studies have researched feeding ecology of demersal fish species in the ocean, little is known about the feeding ecology of demersal fish species in fjords. The aim of this thesis was to investigate the feeding ecology of roundnose grenadier (Coryphaenoides rupestris), a demersal fish species, in two Norwegian fjords. Three hypotheses were predicted; (1) that the diet would consist of mesopelagic fish and invertebrates, and benthic crustacean. (2) That diet and food composition would differ between the fjords. (3) Due to the importance of pelagic prey, a difference in prey composition and food amount would be found as a diurnal pattern, and there will be evidence that grenadiers migrate upwards during day or night to feed on pelagic prey. Stomach content of 303 roundnose grenadiers were analyzed to investigate importance of prey groups and differences between and within fjords. Pre-anal fin-length, weight, gonadosomatic index and hepatosomatic index were measured and calculated. In total, the diet consisted mostly of pelagic and benthic crustaceans, 19 % consisted of non-crustacean taxa. No major differences were found in prey composition between the fjords, with the exception of chaetognaths, which were only found as prey in Masfjord. Size of the grenadier influenced the foraging upon polychaetas and euphasids. Fish from Lustrafjord had more stomach content relative to body weight, while the Masfjord population had a higher distribution of sexually matured fish and more stored resources in the liver. There were no clear diurnal differences in consumed prey taxa or in food amount, but in general, pelagically caught fish contained more pelagic prey. Overall, diet analyses showed that roundnose grenadiers from two Norwegian fjords utilize food resources in both pelagic and demersal zone, and that size has an effect when specializing on specific prey groups such as krill and polychaetas. The feeding ecology of C. rupestris is similar to other populations in the Northwest-Atlantic, and they feed mostly on Amphipoda, Copepoda, Euphausiacea, Polychaetae and Mollusca, and are classified as 2nd or 3rd carnivorous consumer. Low amounts of fish found in the stomach content revealed that they rarely feed on fish. Diet consisted both of pelagic and benthic prey, no clear diurnal differences were found. Although the importance of pelagic prey was found, a diel vertical migration pattern could not be confirmed.
PublisherThe University of Bergen
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