Global warming has caused many pelagic marine species to shift their distribution further north. The NE-Atlantic mackerel is such a species, and since 2006 has been caught in increasing number by the commercial pelagic fisheries of Iceland. Such an expansion of feeding grounds can affect the feeding of indigenous fish populations such as Gadoids and Clupeids. Results from a study by MRI on stomach content of mackerel in 2009-2011 showed that mackerel entering the Icelandic EEZ during the summer period increased their body weight by around 42%. Remains of commercially important fish species were identified in the stomach contents, and some overlap in prey items with herring was also found.

To build on these results, this PhD project will use a combined approach to determine in detail the diet of mackerel that migrate to Iceland during the summer, in an effort to understand the ecological impact that this species may have on the ecosystem. The approach will include analysing visual data supplemented by stable isotope analysis and DNA based species identification to provide a more complete picture of the mackerel’s diet. Stable isotope (δ13C and δ15N) signatures reflect biologically assimilated nutrients from the diet over a long time period. Meanwhile DNA based species identification (Real-Time PCR and DNA barcoding) enables difficult prey items, such as those that have been partially digested, or juveniles to be identified. The integration of all these analyses will allow a more detailed insight into the diet of mackerel feeding within the Icelandic EEZ.