The PNAS paper confirms salmon farms are the “main source” of lice on juvenile salmon. But their conclusion that sea lice from salmon farms do not harm wild salmon is flawed. Many teams of scientists have examined the pink salmon numbers in the Broughton. This team clumped all the rivers together which means not all the runs had the same exposure to salmon farms. Other teams have examined each run individually and these two methods give opposite results. There is no reason to doubt the work that examines each run. If these authors want to champion their methods they need to explain why it is more accurate.
The authors suggest that salmon farms may actually benefit wild salmon, that perhaps sea lice are a valuable source of food for juvenile salmon that can improve their productivity. This is based on an observation I made in a paper and it is completely out of context. It was an exceptional observation which is why I wrote about it.
The findings in this paper run contrary to international research that has shown farm-origin sea lice threaten wild salmon populations. In 2003, Norway responded by establishing National Salmon Fjords to protect wild salmon from salmon farms. In 2008, the BC government prohibited expansion of the industry onto the central coast.
This paper is a distant outlier to a growing international body of literature pin-pointing decline in wild salmon populations near salmon farms they cannot simply ignore the weight of evidence stating an opposite conclusion. They need explain why they found the opposite.
The severe physical impact of sea lice on juvenile salmon is indisputable. If these authors want to say some other disease is killing sea lice infested salmon, they need to provide actual medical data, not just theory.