Data from: Feeding ecology of Northeast Atlantic mackerel, Norwegian spring-spawning herring and blue whiting in the Norwegian Sea

The Norwegian spring-spawning (NSS) herring (Clupea harengus), blue
whiting (Micromesistius poutassou) and Northeast Atlantic (NEA) mackerel
(Scomber scombrus) are extremely abundant pelagic planktivores that feed
in the Norwegian Sea (NS) during spring and summer. This study
investigated the feeding ecology and diet composition of these
commercially important fish stocks on the basis of biological data,
including an extensive set of stomach samples in combination with
hydrographical data, zooplankton samples and acoustic abundance data from
12 stock monitoring surveys carried out in 2005-2010. Mackerel were absent
during the spring, but had generally high feeding overlap with herring in
the summer, with a diet mainly based on calanoid copepods, especially
Calanus finmarchicus, as well as a similar diet width. Stomach fullness in
herring diminished from spring to summer and feeding incidence was lower
than that of mackerel in summer. However, stomach fullness did not differ
between the two species, indicating that herring maintain an equally
efficient pattern of feeding as mackerel in summer, but on a diet that is
less dominated by copepods and is more reliant on larger prey. Blue
whiting tended to have a low dietary overlap with mackerel and herring,
with larger prey such as euphausiids and amphipods dominating, and stomach
fullness and feeding incidence increasing with length. For all the species
feeding incidence increased with decreasing temperature, and for mackerel
so did stomach fullness, indicating that feeding activity is highest in
areas associated with colder water masses. Significant annual effects on
diet composition and feeding-related variables suggested that the three
species are able to adapt to different food and environmental conditions.
These annual effects are likely to have an important impact on the
predation pressure on different plankton groups and the carrying capacity
of individual systems, and emphasise the importance of regular monitoring
of pelagic fish diets.