Norwegian Institute for Nature Research and Rådgivende Biologer researchers have found that interbreeding between farmed salmon and wild salmon is changing the life cycle of the wild salmon. This research paper has been published in the journal Science Advances. The researchers describe their study of scale growth patterns in thousands of salmon taken from rivers in Norway over the years 2010 to 2017.
The researchers reviewed the impact of escaped farmed salmon breeding with wild salmon. They have gathered scales from 6,900 adult wild Atlantic salmon living in 105 rivers in Norway over a seven-year period. They have analysed each of the scale sample patterns and compared them with other fish. The team of the scientists also conducted genetic tests on the scales to learn the genetic history of the fish that donated them.
Scientists found that the biggest impact on the wild salmon came early in life. At a time when salmons were in the process of adapting themselves to live in saltwater. Scientists found it happened in fish with farmed ancestors earlier than in wild fish with no farmed ancestry. They also found that the salmon with farmed fish backgrounds aged at a faster pace and also returned to rivers earlier to lay their eggs. They found female salmon with farmed ancestors grew to maturity 0.29 years earlier than native wild fish, and the number for males was 0.43 years.
The team of the scientists suggested an accelerated maturation process puts the salmon at higher risk from predators. As they are less well-equipped to evade capture by large, fast creatures such as sharks or halibut. Previous study has also shown that salmon with farmed ancestry are less afraid of predators and are bolder and more aggressive in general. They said the overall impact of the interbreeding of salmon will be reductions in wild populations. They have also noted that such reductions have already been observed in some areas.