Category Archives: Mathematics
The true salmon feedlots
There’s one more point we wanted to make about on-land salmon farms as a follow-up to our last post.
Critics of salmon farms love to use the term “feedlot” to describe ocean farms. In their minds this brings a negative connotation to salmon farms (even though science is showing that feedlots may actually be more “green” than finishing beef on grass).
They try and paint word pictures of cramped quarters where poor farmed fish can barely move.
Yet these same people turn around and promote land-based salmon farms as the best possible way to raise salmon.
Either they’ve never bothered to research the numbers, or they are lying when they say they care about fish welfare. Because the latest land-based salmon farm, currently under construction near Port McNeill, will be operating with fish in their tanks at a density of 90 kilograms per cubic metre.
Based on our conversations with the different farming companies, a conventional ocean salmon farm operates with fish in the nets at a density of about 18 kilograms per cubic metre.
This land-based farm will have fish in a density equivalent to 2.6 salmon in a bathtub.
A conventional ocean farm has fish in a density equivalent to 0.5 salmon in a bathtub.
Which one is the true feedlot?
A true salmon feedlot. And the linked article makes a lot of assumptions to suggest that this is profitable! See DFO’s feasibility study for a thorough economic comparison.
One last thought: if animal welfare is truly your concern, take a look at this report from 2007, titled “Closed Waters: The Welfare of Farmed Atlantic Salmon, Rainbow Trout, Atlantic Cod and Atlantic Halibut.” The report suggests, based on an analysis of several different studies, that the top density for farmed Atlantic salmon in ocean farms is 22 kilograms per cubic metre. Salmon farmers are well below this threshold. The report also points out that salmonids in higher densities can be more aggressive, grow smaller, nip and bite at each other, are more susceptible to illness and disease, and get worn fins.
Again, which form of salmon farming is the true feedlot?
Growing awareness of aquaculture is prompting people to start calling for welfare rules for farmed fish. We agree this is necessary.
And we are confident that salmon farmers in the ocean are already above reproach when it comes to looking after the health of their livestock.
Sea lice science ain’t done yet
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.
Shedding
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 [67] reduces the predicted mortality of pink salmon owing to salmon louse infection by 95% relative to an earlier model where shedding was not considered [10]. 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.
Ionoregulation
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.
Conclusions
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 [70], 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 [71]. 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.
