During the last few decades, many wild Atlantic salmon populations have declined. One possible contributing factor for the decline is reduced prey availability at sea.
The condition factor of young Atlantic salmon sampled at sea was reduced in the period 2003–2012. Photo Audun H. Rikardsen
In this new study, the diet of Atlantic salmon captured during trawling surveys in the ocean over a 25-year period was examined. These were young salmon that had stayed a few months at sea.
- Was their diet, or stomach fullness, changed over time?
- And what about their conditions factor, which means how fat they are, was that changed over time?
Poor feeding and reduced condition of the salmon in the years after 2000
The most notable result in this study was a clear reduction in condition factor for the Atlantic salmon sampled in the Norwegian Sea in the period 2003–2012. The stomach fullness was also reduced in the same period, which means the fish had been eating less.
Less high-quality food
The lead author of the new publication, Kjell R. Utne from Institute of Marine Research in Norway, emphasises that “the reduced condition of the young salmon was not only caused by the salmon eating less, but also by the quality of what they were eating”.
He explains further that “there was a reduction in energy efficient fish larvae and Amphipoda crustaceans in the diet. Feeding on other prey, such as meso-zooplankton and insects, cannot substitute the high-quality fish larvae and Amphipoda in their diet.”
This study provides new documentation on how salmon feeding in the Norwegian Sea are affected by reduced feeding conditions during their first months at sea. Possible causes for the observed changes in post-smolt feeding are ocean warming, decreased primary productivity, and reduced recruitment of important fish larvae.
Read the new publication here
Utne, K.R., Pauli, B.D., Haugland, M., Jacobsen, J.A., Ó Maoiléidigh, N., Melle, W., Broms, C.T., Nøttestad, L., Holm, M., Thomas, K. & Wennevik, V. 2021. Poor feeding opportunities and reduced condition factor for salmon post-smolts in the Northeast Atlantic Ocean. ICES Journal of Marine Science https://doi.org/10.1093/icesjms/fsab163