Data from: The feeding ecology of invasive pink salmon Juveniles in northern Norwegian rivers and their role as prey to native Salmonids

Increasing numbers of invasive Pacific pink salmon (Oncorhynchus
gorbuscha) are spawning in northern Norwegian rivers, leading to large
numbers of juveniles migrating to coastal waters. This raises concerns
about food competition in rivers with native salmonids, although details
about the timing and intensity of pink salmon feeding and the
characteristics of their freshwater diet remain unclear. Some evidence
indicates that pink salmon can also serve as a food source for native
salmonids, as do the carcasses of spawned adults, eggs and juveniles. This
study investigated largely unexplored aspects of the emergence timing and
feeding behaviour of juvenile pink salmon. The prevalence, timing and
impact of fish size on freshwater feeding was examined across 10 rivers in
northern Norway, using stomach content and stable isotope (δ13C and δ15N)
analyses to assess diet composition. Similar methods were applied to
assess whether native juvenile salmonids feed on pink salmon tissue, such
as juveniles, during their migration. Predictions of the emergence times
of alevins show that later spawning, thought to cause increased potential
negative interactions with native fish, is an unlikely strategy for pink
salmon in northern Norway. In three of the rivers, some of the largest
free‐swimming pink salmon juveniles sampled in this study (30–35 mm) began
external feeding on freshwater invertebrates later in the season (June and
July), with larval and pupae chironomids as well as blackfly and mayfly
nymphs dominating their diets. Feeding was not observed in all rivers,
highlighting the need for further study on the prevalence and intensity of
freshwater feeding. Stomach content and stable isotope analyses revealed
that some larger native Atlantic salmon and brown trout juveniles consumed
pink salmon juveniles, complicating assessments of their overall impact on
native salmonids.