On sea lice, UFOs and faulty logic: analyzing a new sea lice study

One of our Twitter followers (thanks @farmsalmon4ever) called our attention to a new sea lice study published Jan. 4, 2012 about sea lice epidemics.

The study, titled “Critical thresholds in sea lice epidemics: evidence, sensitivity and subcritical estimation” was published in the Proceedings of the Royal Society’s Biological Sciences journal and was written by Neil Frazer, Alexandra Morton and Martin Krkosek.

We decided to take a read through and see what it says.

Morton and Krkosek have published many studies together on sea lice; their work is the basis for much of the criticism of salmon farms when it comes to sea lice. In particular, they have tried to show that salmon farms amplify levels of sea lice, which are naturally present in the ocean.

The problem, they have tried to show, is that farmed salmon provide a place where sea lice can survive and increase their numbers at times of the year when lice levels would naturally drop.  This, they then conclude, threatens passing juvenile wild salmon which have to contend with unnaturally high levels of sea lice around salmon farms.

But, as we asked in our last post, have sea lice from salmon farms harmed wild salmon?

After more than a decade of extensive research, scientists are divided, with the only real consensus being “maybe, but we’re not seeing it,” a conclusion which was recently reiterated by scientists at the Cohen Commission (see project 5).

While farms may increase the number of sea lice in a small area, scientists see no meaningful connection between farm lice levels and actual productivity of wild salmon stocks.

And doomsday prophecies that sea lice would wipe out wild salmon have been proven wrong.

So where does that leave us? Again, in the world of “maybe, but we’re not seeing anything definitive.”

Reverse-engineering epidemic data

This new paper by Frazer, Morton and Krkosek is different than many of their previous sea lice studies together because it appears to be more of an attempt to develop a tool to better understand and predict sea lice levels than an attempt to prove anything.

The paper presents a mathematical model for predicting how many farmed fish should be allowed in an area before they reach a threshold and pose a risk of sparking a sea lice epidemic.

“Two observations motivate this paper,” they write. “One is that sea lice are seldom a problem in areas with low production even when lice are present on local wild hosts. The other is that lice are seldom a problem when sea-cage aquaculture is new to an area.”

It takes several farm production cycles and increasing density of fish to spark any notable increases in sea lice, they continue.

To prove this, the authors use the examples of a sea lice epidemic in New Brunswick in 1994 and an epidemic in the Broughton Archipelago in 2001, taking the numbers from the epidemic, reverse-engineering them and calculating the threshold beyond which stocking densities in salmon farms can provoke a sea lice epidemic.

Bad logic

There are problems with this. The study doesn’t have very much data for the Broughton Archipelago. “Lice data during subcritical stocking in the area are not available because monitoring of lice began after the epidemic emerged. However, assuming that the critical stocking threshold was exceeded in 2000-2002, the critical band is estimable.”

Wait, what?

That is a BIG assumption to make. The authors are assuming that because there was an epidemic of sea lice in 2001, farms must have exceeded the critical stocking threshold for the region.

Frazer, Morton and Krkosek are assuming their theory is right based on completely circular reasoning.

  • They believe there is a “critical threshold” for the amount of farmed salmon which can be in an area.
  • They believe that beyond that threshold there will be sea lice epidemics.
  • There was a sea lice epidemic in 2001.
  • Therefore salmon farms crossed that “critical threshold.”

It’s fallacious reasoning. Using that logic, we could argue that:

  • We believe UFOs are real.
  • We believe UFOs leave crop circles.
  • There was a crop circle in the farmer’s field this morning.
  • Therefore UFOs are real.
A crop circle
This showed up in the field yesterday. Therefore UFOs are real.

Just like the UFO believer fails to consider that crop circles may have come from something other than a UFO, this paper fails to consider that a sea lice epidemic may have been prompted by something other than salmon farms.

The study also seems designed to reach the conclusions the authors were looking for.

“For the Broughton Archipelago, the Pacific Salmon Forum (PSF) recommends limiting Broughton Archipelago farmed salmon production to less than 18.5 kilotons per year,” it says.

How convenient that is just about exactly where the authors estimate the “critical threshold” production levels for the region.

Production level critical threshold

A useful tool

Before anyone thinks we are trying to dismiss this study out-of-hand, we want to point out that it actually provides quite a useful tool. It considers water temperature and salinity, which can have a huge impact on sea lice abundance, and the model could be adjusted to help farmers forecast and plan production cycles.

“If changes in temperature and salinity could be forecasted, farmers could pre-emptively harvest or treat,” the authors write. “Also, locating farms in low-saline conditions may raise threshold values and prevent epidemics.

“Thus, if good records are kept while an aquaculture industry expands in a particular region, the critical stocking level can be estimated without ever experiencing an epidemic.”

This could be very useful for salmon farmers, who now have more than a decade’s worth of sea lice data as well as salinity and temperature data and would love to be able to keep sea lice levels as low as possible.

However the authors err by assuming their model is right.

Perhaps someone could take the decade of real-world data that is out there, plug it into this mathematical model and see if it actually lines up with any observed increases in sea lice levels on wild salmon. Then we would know if it’s right or not.

Perhaps the authors should have done that themselves.

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5 thoughts on “On sea lice, UFOs and faulty logic: analyzing a new sea lice study”

  1. The one thing that has always annoyed me about Morton and her colleagues is their rampant abuse of science. The scientific method, in its most basic terms, is to ask a question and then test various hypotheses to come up with an answer. It seems to me they always start with an answer and test until they find a question that suits them.

  2. Ai yi yi. You refer TWICE!!?? to a “2001 sea lice epidemic”. there was no such thing. You know this. There was no data anywhere to support this assertion. There was a massive collapse following a massive spike in returns; a classic boom and bust scenario. you MUST correct this. A lie oft repeated can become the truth, surely you fine chaps are not now buying this lie oft repeated.

    Also, no article on sea lice in BC can go without mentioning the work by Simon Jones about how virtually immune pacifics are to sea lice. Or Saksida’s study showing ZERO evidence that any fish in the Broughton died from sea lice. But that aside, please correct your referral to a sea lice epidemic. There was no evidence of an epidemic, sea lice or otherwise, in 2001 or at anytime. There have been outbreaks on wild salmon held too long pooling, waiting for rivers to rise. The last one recorded was in Alberni Inlet in the early 90’s I believe among sockeye.

    1. We understand that you don’t like the word “epidemic” and you are correct to reject its use because in the strictest sense, an epidemic refers to an outbreak of a disease which affects people.

      The correct term to use for sea lice on fish is epizootic, an outbreak of disease or pathogen affecting animals.

      However, for the sake of discussion, most people don’t make the distinction between the terms, and in numerous scientific papers and discussions they are used interchangeably. The paper described above does this; we analyzed it using the authors’ own terms.

      And we don’t want to dismiss the observational data collected by Morton et al in 2001 which they believed indicated an epizootic. Their data shows an above-average amount of sea lice; what exactly that means, and how accurate the data is, is a subject of debate. But we don’t want to dismiss it out of hand.

      And as we pointed out, Marty and Saksida show with 60 years of pink salmon data that the increased amount of sea lice in 2001 has nothing to do with pink salmon returns.

      We would also like to point out that sea lice epizootics do happen naturally, and have been documented. This is a good overview:

      L. salmonis is native and prevalent (endemic) to the North Pacific and Atlantic oceans. In the Pacific, sea lice monitoring programs have reported the occurrence of sea lice on 91 to 92 percent of fish sampled, with a mean intensity of between 5.83 and 11.9 lice per fish (Nagasawa, 2001; Beamish et al., 2004, 2005) on Pacific salmon. A prevalence of 90 percent sea lice on pink and chum juvenile salmon was reported by Morton et al.(2004) for the Broughton Archipelago. With such a high prevalence of sea lice in areas with and without salmon farms, it is to be expected that the combination of currents, temperature, and salinity necessary for a sea lice epizootic will on occasion occur. Such epizootics have been well documented for a century, well before salmon farming was introduced (Calderwood, 1906; White, 1940; Johnson et al., 1996).

      Thanks for your comments!

      1. The sea lice level in 2001 was not found to be above average as there was no baseline data with which to compare it. In factI dont even think data was collected until 2002. Morton’s first article was roundly criticized for its poor sampling techniques, using different sampling techniques in different regions. Beginning 2002 DFO used standardized, proper, sampling for sea lice on wild juveniles, and it it is true subsequent years did show lower levels of sea lice- completely contrary to Morton’s predictions and own findings.

        I am not concerned with the use of the word epizootic or epidemic. The better word would be “higher levels”. These higher levels asserted by Morton and discredited by real scientists were found to be at levels orders of magnitude lower than true epizootics such as in Alberni Inlet in the 90’s and orders of magnitude below the lethal dose of sea lice determined in a laboratory by Simon Jones.

        Please point to a non fish farm activist, peer-reviewed, paper that refers to the sea lice levels of 2001 as epizootic,without being prefaced with the word “alleged”. We now have 10 years of sea lice population data and yes 2001 may have been the highest year in some categories, for some months, but that nowhere near qualifies it as an epizootic event. As it was the first year ever that such sea lice data was collected, and done so by psychotic anti fish farmer rather than a trained fisheries scientist the result is beyond suspect and cannot be referenced seriously, let alone as an epizootic.

  3. Apart from appearing to have been designed to achieve exactly what they wanted to show, the modelling used seems to have a major flaw:
    What about everything that eats sea lice?
    Studies (and common sense) show that mussels eat sea lice larvae:
    http://umaine.edu/news/blog/2011/04/27/umaine-researchers-make-key-discovery-in-war-on-sea-lice-infestations/
    Salmon farm infrastructure is habitat for countless filter and detrius feeders – they wouldn’t be there if there wasn’t anything to eat.
    Outside of the farm lice would make up a portion of the zooplankton that feeds, among other things, juvenile salmon. (Just a thought…)
    If you can’t account for natural control past mortality (which they pegged at 1 per day, along with 1 not making it to motile stage) the resulting number of potential parasites is entirely in question.
    It’s like modelling climate without factoring in clouds.

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