Genetics and the salmon

Hello, I’m Jamie Stevens, associate professor of molecular ecology here at Exeter. Today I’m going to tell you about population genetics and how they enable us to monitor threatened and over exploited fish species. I’m going to use the example of the wild Atlantic salmon, which is at risk in most parts of eastern North America and Europe. Like most salmonic fish, Atlantic salmon start their life in freshwater and they migrate to sea to feed before returning again to freshwater to spawn and to continue their life cycle. The fidelity with which salmon home to the rivers where they are born is well known, and has been the focus of many wildlife films.

But not only is the fidelity of homing part of a truly amazing life cycle, it also allows us geneticists to track and monitor salmon populations by their genetic signatures. A genetic signature is a group of genes in the DNA of an organism with a pattern unique to the animal or population of animals. Salmon populations develop river specific genetic signatures, because they typically mate with fish closely related to themselves and from the same river. So it is that the homing plays a key role in reinforcing the salmon’s genetic signature. These genetic signatures can be used for identifying, tracking, protecting and managing Atlantic salmon.

For example, by checking the DNA sequence of adult fish caught at sea against the genetic database, we can identify their river of origin. This process of checking DNA sequences is called genotyping. Between 2004 and 2008, my laboratory participated in the Atlantic Salmon Arc Project, which constructed such a genetic database for Atlantic salmon across the species range in southern Europe. Salmon numbers continue to decline in this region, despite improvements in water quality and river access. Primarily, it’s thought, because of the numbers of fish that die at sea. With our project partners in Spain and Ireland, we genotyped more than 4,000 salmon, allowing us to construct a detailed genetic database of the signatures of Atlantic salmon in the rivers across the region.

This provided a valuable tool for studying the impact of commercial fishing on salmon, in a part of their range where they are especially vulnerable. The project has also helped to guide fisheries management and policy, demonstrating the value of genetic analysis in marine conservation.