Of 115 steelhead, 13 were typical, 49 were fat, and 53 were thin. As the chart below illustrates (

click here for larger printable version), fat steelhead have larger divisors than thin ones. This observation is true not only for the average divisor (704 for fat, 675 for thin), but for every point along their respective probability distributions. That is, the entire probability distribution of divisors for fat fish is shifted significantly to the right compared to the probability distribution for thin fish.

This effect is not just a random anomaly of the data, but rather a fact of nature. The

theory of girth taper explains it, our

conical fish model shows how it works mathematically, and our

improved weight estimator incorporates an appropriate adjustment to account for it.