Identifying and Explaining Intensification in Prehistoric Fishing Practices III: Identification of the Fishing Gear Used from the Size-Frequency Distribution of Fish

The previous post concluded that intensification of fishing could be identified from the kind of gear used to capture those fish. Having decided that fish bone assemblages should be subdivided based on the gear used to capture the fish, the issue then becomes: how can we identify that gear? Answering this question requires middle-level theory that can link physical characteristics of the fish assemblage to gear type.

Gear types differ in the sizes of fish that can be captured by them. Nets should capture a larger range of fish sizes than other gear such as hook and line or spear. Hook and line or spears can not effectively capture smaller species. Assemblages formed primarily from net-caught fish should have a larger proportion of small fish than those assemblages that formed from fish primarily caught by hook and line or spear. To verify this intuition, additional sources of data from which middle-level theory could be derived would be very helpful.

Baseline data on the size-frequency distribution of fish from nearshore ocean habitats, drawn from modern sources, could be compared to the size- frequency distribution of fish bone from archeological assemblages. Prehistoric fishers presumably selected a portion of the natural range of variation in fish size through their use of particular fishing gear. Thus, the comparison would facilitate the identification of such selection. Published modern data of this sort are surprisingly rare. Beach seine netting around an estuary in Alaska produced fish assemblages whose size-frequency distributions were largely unimodal with a long tail to the right. The size-frequency distribution of individual species varied from unimodal to multimodal, depending on the number of age-classes present. The applicability of these data as an analogy to fish from my study area can obviously be questioned. I don’t have any reason to believe that the form taken by the Alaskan size-frequency distributions is exceptional, however, and a consideration of the factors that produced these distributions may be useful.

Any nearshore habitat will likely contain a range of species, each represented by specimens from one or more age classes. Different species will vary in mean size within a particular age class. The aggregate of the individual size-frequency distributions is therefore likely to produce a highly variable unimodal distribution, particularly when individuals from many different species are represented. Assemblages formed from a mix of fish caught by net and fish caught by hook and line or spears should have a bimodal size-frequency distribution. The proportion of fish in each mode should reflect the emphasis placed on netting and other fishing gear. Variation in the size-frequency distribution among archeological assemblages should provide some indication of variation in the techniques used to take fish.

© Scott Pletka and Mathematical Tools, Archaeological Problems, 2009.

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