I don’t work on sea lice any more because I figured it out. Where there’s fish farms, there’s sea lice. It’s an extremely easy thing to study, way easier than whales.
— Alexandra Morton, author and co-author of numerous sea lice studies, speaking at the Cohen Commission, Sept. 7, 2011
The science is never done, even if some people think they’ve “figured it out.” And it’s a good thing researchers haven’t given up on researching sea lice in B.C. because we apparently still have an awful lot still to learn.
Six UBC scientists have just published an interesting paper titled “Physiological consequences of the salmon louse (Lepeophtheirus salmonis) on juvenile pink salmon (Oncorhynchus gorbuscha): implications for wild salmon ecology and management, and for salmon aquaculture.” It was published by the Philosophical Proceedings of the Royal Society B and is available to read online (we will be adding the PDF version to our library at a later date).
There is a lot of interesting information in this study, which looked at the real-world physiological effects of sea lice infestation on wild salmon.
For years, critics of salmon farms have claimed that sea lice from salmon farms are killing wild salmon. However, there has never been any evidence to support this claim, only sketchy predictions from mathematical modelling studies.
No one denies that salmon farms can increase the number of sea lice in an area; when wild fish pass salmon farms, the lice, a natural parasite found in the Pacific Ocean, can infest farmed salmon, which can act as a breeding ground for lice if not managed properly.
But what is up for debate is this: IF lice from farms infest tiny pink salmon passing by in the spring months, when they head out to sea, do they have any effect on wild salmon survival?
This new study basically says, “maybe, maybe not.”
But while this is inconclusive, this study makes several interesting new discoveries, and puts old information in a new light.
It’s well-known that juvenile pink salmon can shed sea lice, dependent on a wide variety of factors in the ocean as well as their own physiology. But this new study makes the interesting point that previous mathematical modelling studies, particularly the well-known and well-publicized 2006 sea lice study by Morton, Krkosek et al, are seriously flawed when they do not consider shedding rates.
A high rate of louse shedding is also of importance in mathematical models, where the incorporation of realistic shedding rates  reduces the predicted mortality of pink salmon owing to salmon louse infection by 95% relative to an earlier model where shedding was not considered . Collectively, these findings of high rates of shedding of attached lice suggest that the majority of the salmon lice that successfully infect a fish will be shed before they reach motile and reproductive stages. Clearly, the interactions between salmon lice, juvenile pink salmon and their environment are extremely complex and change temporally as both salmon louse and fish develop and the implications of this need to be considered in relation to conservation efforts.
What is ionoregulation? It’s a self-regulatory process in a salmon’s body which, if it is out of balance, can kill a salmon within days or leave survivors severely crippled. Researchers in this new study decided to see if sea lice can affect this process when pink salmon are at their most vulnerable, right after they enter saltwater. The research found that sea lice can cause an imbalance, but only until the fish are about 0.5 grams, and the implications to their survival is unclear. As well, once the salmon reach 0.7 grams, they have sufficiently increased their ability to resist and shed sea lice.
Sea lice from salmon farms may harm wild salmon, but it’s not certain. The effects of sea lice on tiny wild salmon will certainly have some effect on them at some point, so to reduce any risks, the study recommends that salmon farmers and their managers continue doing what they are doing: voluntarily fallowing farms during outmigration periods to keep sea lice levels low. This is sound advice, and a good use of the precautionary principle.
In a recent study to investigate the benefit of fallowing fish farms in the Broughton Archipelago, it was determined that fallowing reduces salmon louse levels around the farm and reduces juvenile pink infection levels to background levels , indicating that this recommendation and voluntary compliance may mitigate salmon louse effects on the most sensitive stages of pink salmon.
The study closes with a very interesting footnote, which leaves us with the suggestion that in the grand scheme of things, sea lice really aren’t that big of a deal for salmon. The study’s closing paragraph is a perfect way to close this blog post:
Perhaps the only study that has truly considered the impact of salmon louse infection on juvenile salmon is the 10-year study of the return of Atlantic salmon smolts that had been treated with SLICE (emamectin benzoate) to protect them from salmon louse infection for the first 90 days of their outward migration, a period which easily extended beyond the contact with net-pen aquaculture and associated salmon lice. Remarkably, a comparison with non-treated fish revealed that protection of juveniles from salmon louse infection represented a minor component to overall marine survival. Indeed, during the 10-year study, adult Atlantic salmon returns fell a similar 10-fold in both treated and non-treated fish . A similar study on juvenile pink salmon treated with SLICE in the Broughton Archipelago could be very revealing in assessing the true impact of sea lice on pink salmon fitness.
We agree. This study should be done, because the science is never truly finished.