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Other gear like hook

Such distributions can be analyzed using the mixdist package for R. In particular, two modes seem to be present in the cm level, while three modes apparently occur in the cm level.

The other levels are harder to interpret. Other gear like hook and line or spears is much more likely to catch large fish. The next step is to look at histograms of the data, which show the number of fish bone that occur within a particular size interval.

The histogram depicts the original data. The mode of smaller fish should represent fish taken by nets, and the mode of larger fish should reflect fish taken by hooks and line or by spears. The gray bars at the bottom of the graphic show the deviations of the model from the observed distribution. Note that the histogram interval differs from the interval used in the previous graph. The scale of the deviations is depicted in relative terms.

Prehistoric fishers used spears tipped with large stone points or sharpened bone. Recall that I am interested in determining how many of these fish were caught by nets and how many were caught by other gear. Finite mixture distributions model such situations.

The other levels are harder to

Hooks and line or spears may not be able to catch fish smaller than some threshold value of size. Modes, or peaks, in the fish size-frequency histograms should reflect the use of different fishing gear. This analysis is ongoing and has been plagued by some problems that I may have finally resolved. They employed hooks made from shells. These gear should differ in the size range of fish that they are likely to capture.

Clearly, the identification of these modes is not straightforward. Fortunately, statistical techniques exist which may help to distinguish separate populations which are mixed together in a single distribution. Nets may catch both large fish as well as small fish. This model appears to fit the data reasonably well. The lack of more clear-cut patterning likely results from a heavy reliance on nets.