Quote:
Originally Posted by dmtfish
Mathgeek, your hypothesis makes sense. However, I think it is flawed due to the assumption that every fish measured would have been caught near the wiers in strong current, which is obviously not the case.
|
Thanks for bringing this up.
There is no assumption about every fish. Just enough fish (a percentage of the fish sampled) spending time near the weirs over the few months prior to being caught to reduce the mean condition factor.
Think of an analogy with BMI in humans. Suppose 1/3 of the population caught the flu and lost 30% of their body weight. The average weight of the whole population would be reduced by something close to 10%, even though everyone did not catch the flu or lose weight. The average BMI would be lower, even though many humans lost no weight.
The average of a population can be decreased without every fish being decreased.
The opposite would also be true if opening the weirs significantly increased body condition. If only a percentage of the fish dined at the weir buffet and got a lot fatter, the result would be a smaller, but significant increase in the average body condition. Because our measurement methods can determine mean relative condition factors to an accuracy of 1% or so, we can detect relatively small changes in average body condition.