Download Poster Abstract for the ICES Annual Science Conference 2013, for

Trophic interactions of Atlantic mackerel (Scombrus Scomber) and herring (Clupea harengus) on the
Icelandic shelf – a study of diet using stable nitrogen and carbon isotopes.
Cecilia E. K. Kvaavik 1, 2, 3, Guðmundur J. Óskarsson 1, Hildur Pétursdóttir 1, Jonathan Grabowski 4,
Anna Kristín Daníelsdóttir 3 and Guðrún Marteinsdóttir 2.
1
Marine and Freshwater Research Institute, Reykjavík, Iceland. E-mail: [email protected]
University of Iceland, Reykjavík, Iceland
3
Matís, Reykjavík, Iceland.
4
Northeastern University, Nahant, MA, USA.
2
Warming of the world’s oceans has caused many pelagic marine species to shift their distribution especially in a pole wards direction. Pelagic fish populations can be very abundant and may have a
great impact on the ecosystem. Extensive numbers of pelagic fish enter the Icelandic waters during
summer to feed, it is estimated that ~1.5 million tonnes mackerel (Scombrus Scomber) and ~ 3
million tonnes herring (Clupea harengus) enter the Icelandic shelf each year during their summer
feeding migration, indicating that these stocks can exert significant top-down pressures on the food
web. The mackerel are opportunistic feeders and feed on a variety of zooplankton and small fish,
whilst herring are mainly filter feeders of zooplankton. Research into the diets of these two species
suggests that the main zooplankton prey species in Icelandic waters are copepods (primarily Calanus
finmarchicus), euphausiids, pteropods, amphipods and appendicularia. Mackerel also include fish
prey such as larval sandeel (Ammodytes spp.), herring and capelin (Mallotus villosus).
This study focuses on the differences between the diets of these two key pelagic species as well as
the trophic links between them and their lower trophic level prey. This is done by analysing the
stable isotope signatures (δ13C and δ15N) which reflect biologically assimilated nutrients from the
diet over a longer time period. Results of the isotope analysis coupled with stomach content data will
be presented, with focus on the diet composition and estimate of the dietary impact of these two
pelagic species on lower tropic level species.