The Metalog Distributions

Fish Biology Empirical Data

According to the log books of a northern British Columbia fishing lodge, 3,474 steelhead trout were caught and released on the Babine River during 2010-2014. The histogram below shows their distribution of weights.

After having lived in the ocean, many are returning to the river to spawn for the first time ("1-salt"). Unlike salmon, they may go back to the ocean, gain weight, and, a few years later, return to spawn for a second time ("2-salt). 

Fish biologists might model this with a best-fit lognormal distribution (green dots), which cannot capture the bimodal nature of this population. In contrast, as the number of metalog terms approaches ten, its bimodality clearly emerges.

This exampe is discussed further in Section 6.1.1 of the
initial metalogs publication.

Northern British Columbia and Adult Male Steelhead Trout