Body Size of Atlantic Salmon Adapts to Habitat Changes: Study

Image: NOAA Fisheries.

Norwegian researchers have released study results showing that the body size of Atlantic salmon can rapidly adapt to habitat changes.

However, researchers Ingerid J. Hagen and Sten Kaflsson, of the Norwegian Institute for Nature Research in Trondheim, Norway said that understanding how species respond to habitat alternation is hampered by a lack of knowledge of the genetic basis of traits and a lack of data on changes in trails over time.

The study, published by nonprofit news-release distribution platform EurekAlert in October, examined how the body mass of Atlantic salmon adapted to regulations tied to hydropower generation in the River Eira, a sport fishery in western Norway.

There is also a population of sea trout in River Eira, but catch records in sea trout are not sufficient to perform a similar analysis on this species, Hagen said.

The government agency overseeing hydropower production in the river has requested no changes in waterflow based on salmon size, she said, noting that since they have no data on acidity or temperature in River Eira they cannot make any inferences on possible impact of increased acidity or rising temperatures.

The study, which was conducted for a decade, is now finished, but catches are still recorded and scales of catches are collected. The researchers, Hagen said, don’t feel that they can make any predictions regarding body size changes in Atlantic salmon in other rivers as ocean temperatures continue to warm.

The overall study included the body mass of salmon caught in 1925 and 1926 as well as salmon caught between 1940 and 2016. River regulation began in 1953. 

The authors also extracted DNA from 346 salmon scale samples and compared the salmon population in Eira with that from a comparable unregulated river. The results showed that after regulation the waterflow in Eira and the body mass of its salmon both decreased to one-third of the values before regulation.

Genetic analysis identified two genetic loci, vgll3 and six6, in which changes in allele frequency predicted more than 80% of the body mass reduction. Allele occurs when two or more alternative forms of a gene that arise by mutation are found on a chromosome.  

According to the authors, after regulation the mean body mass of the salmon population trailed its optimum value and caught up after around six generations. The findings demonstrate, the authors said, how salmon populations can rapidly adapt to human-caused habitat alteration.