Identifying and Explaining Intensification in Prehistoric Fishing Practices IV: The Relationship between Fish Size and Fish Bone Size

The previous post argued that size-frequency distributions of fish reflect the gear used to capture those fish. Middle-level theory, however, must also verify that the size of fish bone reflects live fish size, since archeological deposits will only contain the bones and not whole fish. In general, the size of particular animal parts reflects overall body size.

Previous studies of a number of species have demonstrated a strong, positive relationship between vertebra size and fish size, allowing inferences to be made regarding the original size of a fish based on vertebra size. The exact nature of this relationship varies by species and by the specific vertebra measured.

For my midden assemblages, vertebrae seem to be a useful bone type on which to focus. Vertebrae are generally the most well-represented bone type among all of the species likely to occur in these midden assemblages. Vertebrae will therefore be most likely to provide adequate sample sizes for further analysis.

Ideally, we should obtain multiple specimens for each species represented in the middens and develop functions relating bone size to fish body size. Such a project requires large collections, spanning dozens of species and including a range of sizes for each species. Most faunal analysts probably do not have access to collections of this scope.

A preliminary analysis using a variety of common species from my study area demonstrates that a positive relationship between vertebra size and fish size exists among many species of bony fish (teleosts). The individuals used in the analysis derive from an unsystematic sample of specimens for which live weight had been recorded. The table provides the data, which are illustrated in the graph.

Fish Live Weight and Vertebrae Measurements

Fish Live Weight and Vertebrae Measurements

Fish Live Weight and Caudal Vertebra Height Scatterplot

Fish Live Weight and Caudal Vertebra Height Scatterplot

The graph shows that a positive relationship obtains between vertebra size and live weight for the specimens in this sample. An inspection of the graph might be sufficient to establish that vertebra size reflects fish size. The exact nature of this relationship will be important for some of the analyses that I will do later. For this reason, I would like to model this relationship more explicitly. In the next post in the series, I will begin this task.

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

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