A recent BBC report says the distinct genetic characteristics of salmon populations in Spain are being lost as a result of climate change and human interference.
According to the new agency, a team of UK and Spanish researchers say disrupting the species' migratory behavior and strong homing instinct could have long-term consequences.
They added that they were working on ways to "disentangle" the effects of climatic changes and anthropogenic factors (fisheries management practices).
The findings appear in the journal Global Change Biology.
The BBC notes the team's study focused on the changes recorded over a 20-year period to Atlantic salmon populations in Asturias, Spain considered to be the "vulnerable" southern limit of the species' natural range.
"Salmon develop quite distinct population structures because of their ability to home to their natal rivers," explained co-author Jamie Stevens, from the University of Exeter's School of Biosciences.
"If you have such a defined system, they will quite quickly develop genetic profiles that become definitive to a particular river system."
He said the unique characteristics meant that the fish adapted to the conditions found within a particular river.
"There is a whole bunch of things: river chemistry, ability of the fish to withstand things like temperature, behavioral factors like run time to the sea and return time to spawning grounds," Dr. Stevens told BBC News, noting that those local populations have a range of adaptations that can give the fish an advantage within that river."
The study identified two distinct periods. Until 1992, there were a lot of "foreign" fish being introduced to the river systems, from more productive rivers in other parts of Europe, to suit anglers who want bigger fish on their lines. After 1992, this practice was halted but there is still not a big recovery towards the genetic differences that is a signal of healthy populations.
Previous studies had suggested that increased water temperature was linked to an increase in fish straying between rivers and a breakdown of population structures.
"Increased water temperature appears to disrupt the fidelity of salmon returning to their natal rivers," said Dr. Stevens.
In their paper, the researchers from the universities of Exeter, UK, and Oviedo, Spain attempted to untangle how the different factors were undermining the salmon population structures of the five rivers.
Dr. Stevens explained that salmon was often used as an indicator for the state of rivers.
"Monitoring a fish that is a top predator gives you a really good feel for the overall health of river systems that you might want to manage."
