More sea lice science based on bad assumption

We’re glad to see people are still studying sea lice and salmon in B.C. despite Alexandra Morton’s assertion that she’s “figured it out.”

But it’s disappointing that the latest research to come out relies on an assumption that was shown to be flawed five years ago.

A new paper by Stephanie Peacock at the University of Alberta, written with scientists who have made careers out of finding spurious connections between salmon farms and wild salmon population numbers, claims to show that salmon runs in the Broughton Archipelago have been bouncing back ever since salmon farms in the area started co-ordinating sea lice treatment.

The paper is right about one thing: adaptive management (in this case, timing of SLICE treatments) reduces the number of sea lice on farmed salmon at the appropriate time of year. The data clearly shows this.

However, the rest is all assumption, and ignores other studies done in the region which came to different conclusions, including one including as co-author Marty Krkosek, who also co-authored Peacock’s paper, showing “no statistical difference” in survival between juvenile salmon which passed salmon farms and those which did not.

It’s disappointing that in 2012, after so much research has been done on the lifecycles of sea lice and wild salmon and how they interact, that this study assumes that levels of sea lice on juvenile salmon are only influenced by farms and by nothing else. This is clearly false. Sea lice have been around for millennia before salmon farms, having evolved specifically to parasitize salmon.

It’s also disappointing that this study assumes that mortality of wild salmon is due to sea lice. Really? Like there’s nothing else in the ocean which could have killed them by eating them, perhaps?

But the worst assumption is that in this study the authors assume that there was no “epizootic” episodes of sea lice in the 1990s. We don’t know if there were or not because no one recorded any such episodes. But there were definitely a lot of sea lice around back in the day.

Sea louse
Onions and garlic will not kill me, fools! Mua ha ha!

There was a lot of trial and error going on in the early days of salmon farming in B.C. and sometimes there was a lot of error. In the 90s, farmers had to scrape the sea lice off their harvest-size salmon. They had no effective treatments at that time. Ivermectin (no longer used in B.C.) wasn’t very effective. Desperate farmers even tried using onions and garlic which didn’t work either (sea lice, while parasitic, are not vampires). SLICE hadn’t been developed yet.

There were a lot of sea lice around in the 1990s, and despite that, the pink salmon returns in the Broughton in 2000 were at record-high numbers.

So starting from that record-high number to declare a decline is a bad assumption.

Using the same logic that Peacock et al use, we could argue that increasing salmon farm production with no effective sea lice treatment prior to 2000 leads to increased pink salmon productivity. When you put the data side by side (as we did in the graph at the top of this post), you could make a convincing case. See? Increased production and no sea lice control is obviously correlated with a fantastic explosion in pink salmon populations.

That’s silly, of course. But no sillier than arguing farms caused a decline on the other side of the line after the amazing 2000 run.

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