the role of assumptions…

If you ask a physicist how long it would take for a marble to fall from the top of a ten-storey building, she will answer the question by assuming that the marble falls in a vacuum. Of course, this assumption is false. In fact, the building is surrounded by air, which exerts friction on the falling marble and slows it down. Yet the physicist will correctly point out that friction on the marble is so small that its effect is negligible. Assuming that the marble falls in a vacuum greatly simplifies the problem without substantially affecting the answer.

The art in scientific thinking — whether in physics, biology, or economics — is deciding which assumptions to make. Suppose for instance, that we were dropping a beach ball rather than a marble from the top of a building. Our physicist would realize that the assumption of no friction is far less accurate in this case: Friction exerts a greater force on a beach ball than on a marble because a beach ball is much larger. The assumption that gravity works in a vacuum is reasonable for studying a falling marble but not for studying a falling beach ball.

More from one of my economics textbooks…

Thus my questions to fisheries biologists that came up with the concept of Maximum Sustainable Yield (MSY) is this: when we assume… are wild salmon a marble falling from a building, or, more like a beach ball?

_ _ _ _

See, for about 50 years, wild salmon (and East Coast cod) have been largely “managed” by the concept of Maximum Sustainable Yield. It’s based largely on the scientific assumption that habitat for salmon (ocean or freshwater) remains static over time and will produce a similar amount of baby salmon every year, which will swim out to the ocean (the pasture), and return in similar numbers 4 or 5 years later.

(MSY is a great assumption for farming fields… maybe not so much for looking after an essential species that depend on a range of ecosystems including the North Pacific).

Not only that, MSY as practiced, suggests that humans can kill 80% of a predicted salmon run, and assume that the remaining 20% that “escape” fisheries will reproduce the same size run in perpetuity.

In essence, fisheries biologists (employed by Departments of Fisheries and Oceans and running hallowed halls of educational institutions) assumed that wild salmon were a marble falling from the building (in a vacuum). See the evidence in this recent graph produced by the Pacific Salmon Commission and placed in the Dec. 09 Salmon Think Tank convened by Simon Fraser University in Vancouver.

Percent of Fraser River sockeye harvested each year

So there you go… 40 years of taking about 80% of the estimated run. Then in the early 90s that marble in a vacuum became a cannonball. (Or, “oh shit…”)

Now the worst part about this whole story is that Maximum Sustainable Yield (MSY) is still an essential component of ‘managing’ wild salmon in Canada. It’s in the Wild Salmon Policy

Wild Salmon Policy and MSY

And it’s in this year’s 2010 salmon “management planning” documents. Curiously… it’s not called MSY in the 2010 Fraser Sockeye Escapement Strategy. It simply states that killing 60% of some of the sockeye runs is the goal (no… wait, sorry… it’s “mortality”; not kill).

This is a cut and paste from the first page:

Note: "low abundance" (DFO oxymoron)

So take heart… as I’ve heard a DFO rep explain to me recently: “look we’ve reduced MSY to 60% from 80%”… as if that was a step in the right direction…

This is also directly related to the continued mantra from fisheries folks everywhere: “it’s complex, we just don’t know what’s causing these dramatic declines… could be the ocean… could be climate change… could be [enter externality here]…. could be [enter lack of taking responsibility here]”

_ _ _ _

So… assuming that a salmon swims upstream — in a vacuum — or, falls from a building — in a vacuum — (wait… what falls faster a humpy or a sockeye…?  A chum or a spring?)

… what sort of things are we “assuming” out of our equations for achieving MSY? (like the friction on the falling marble, or on the falling beach ball)

Well… there’s those darn seals, orcas, eagles, osprey, bears, squid, mackerel, sharks, parasites, disease, river rapids, hot water, and so on, and so on.

Those darn critters and externalities exert a bit of ‘friction’ on the upstream migration of salmon and successful spawning. Not to mention, the ‘friction’ exerted on baby salmon as they arise out of the gravel and begin their journey downstream and ocean-bound (like all of our shit, prozac, cialis, pulpmill effluent, urban paved road run-off, and so on…)

Just as “Assuming that the marble falls in a vacuum greatly simplifies the problem without substantially affecting the answer”… assuming that wild salmon swim in a vacuum greatly simplifies the problem; however, it also greatly affects the answer. Especially, when the answer = n salmon that we can kill according to MSY equation.

The problem is that Fisheries and Oceans and other North American fish managers have been ‘managing’ salmon according to assumptions that wild salmon are like a marble falling from a building in a vacuum.

When in fact, they are significantly more like a beach ball, which sways all over the place as it falls, and may even go back up on the right updraft… and might get eaten or maimed by some several hundred other things on its journey to the ground. Added, that some of those ‘several hundred other things’ depend greatly on the annual falling of beach balls — in other words the “friction” is essential to life of all involved.

As with the lower benchmark, the upper
benchmark will also be determined on a case-bycase
basis depending on the species and types of
information available, and may apply:
• A proportion of the number of spawners (S)
estimated necessary to provide maximum
sustainable yield (MSY) on an average
annual basis given existing environmental
conditions (e.g., Smsy

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