UK organisations complete study on wild salmon conservation
A new study, a collaboration between the River Carron Conservation Association (RCCA) and the Institute for Biodiversity and Freshwater Conservation at UHI Inverness, offers one of the most comprehensive investigations of conservation stocking of salmon in the United Kingdom.
The study was conducted in the wake of wild salmon populations in Scotland having declined to such an extent that conservation stocking may, in some rivers, be the only option available to prevent the complete loss of the threatened populations.
The partners deem well monitored studies to be therefore essential to maximise the long-term success of conservation programmes and establish best practices to eliminate the potential genetic risks and ecological impacts traditionally associated with stocking.
The report shows that fish stocked as eggs or juveniles survive to return as adults and in some years account for over 50 per cent of the rod catch. Importantly, the study also provided crucial insights into ecologically sound methods for mitigating population decline and, in some cases, restoring the DNA integrity of wild populations.
The report draws from an archive of recently analysed genetic material and other data, collected over three decades by RCCA scientist Bob Kindness, to accurately differentiate between wild-spawned and stocked salmon across multiple generations.
Among the learnings, the study revealed that by breeding from wild-caught fish in the hatchery for a single season, rather than retaining females in captivity for multiple breeding cycles, it is possible to mitigate the risks to long-term genetic health associated with captive broodstock programmes.
It also demonstrated that fish released at the autumn (late) fry stage exhibit significantly higher survival rates compared to those released at different life stages.
"Before the Carron Conservation Programme, salmon stocks had dropped so low that the native fish faced real risk of extinction," said Kindness. "Once the programme was underway, a clear correlation emerged between the number of fish stocked and the number returning as adults."
As expected, genetic material from Norwegian strains, introduced by commercial aquaculture escapees, was detected in both wild-spawning and captive broodstocks. However, the RCCA stocking programme does not appear to be increasing the level of Norwegian DNA beyond what would occur naturally in a wild-spawning scenario.
The study also highlighted a strategy that could actively reduce Norwegian ancestry in the wild population. Incorporating fast-turnaround genetic testing into conservation stocking programmes could enable selectively avoiding breeding from genetically compromised fish.
RCCA said that while this approach may not yet be fully practical, it represents a critical step toward best-practice conservation protocols for mitigating Norwegian aquaculture introgression in wild salmon populations.
Lastly, the study offered key lessons on mitigating some of the negative effects traditionally associated with stocking, while also presenting a potential means to reduce the genetic impact of Norwegian aquaculture strains on wild salmon populations, delivering insights that will guide best practice in future conservation programmes.
