Weighing vs. Counting Shellfish Remains: A Comment on Mason, Peterson, and Tiffany

Abstract

Mason et al. (1998) argue in a recent article that weight as a form of data quantification in the analysis of shellfish remains should be replaced with estimates of the Minimum Number of Individuals (MNI) based on identification of “nonrepetitive” elements (NRE) such as the hinge of a bivalve. Their comparisons of the two forms of shell data quantification lack relevance, and they fail to recognize difficulties in identifying nonrepetitive elements on many kinds of shells. Although weight of shells has its shortcomings, it is still the most appropriate form of quantification in many contexts. A more fruitful viewpoint would be to consider ways in which weight and MNI (or NRE) might complement each other in addressing research questions.

Loco or no Loco? Holocene Climatic Fluctuations, Human Demography, and Community Based Management of Coastal Resources in Northern Chile

“…This is particularly relevant when comparing numbers of robust shells (such as C. concholepas-loco) with lighter shelled animals (such as Perumytilus purpuratus-chorito). Glassow (2000) has also argued that both can be used to complement each other in situations where results can be skewed, whereas Mason et al (2000, p. 760) stated "MNI and weight yielded different results but did not demonstrate that one set of results was 'better' than the other." Most of the stratigraphic units contain highly fragmented shells, however, so the identification of non-repetitive elements (NREs) for most specimens was not possible.…”

“…Shells were then weighed following Glassow (2000). Usage of Ages reported are linked to the different stratigraphic units defined by each author and all were calibrated using the southern hemisphere SHCal13 curve (Hoggs et al, 2013) and the Marine13 (Reimer et al, 2013) for terrestrial and marine samples, respectively.…”

A Test of Ideal Free Distribution Predictions Using Targeted Survey and Excavation on California’s Northern Channel Islands

“…Shell and meat weight data are normalized to a volume of 1 m 3 for comparison. We analyze shellfish and other faunal materials by weight rather than minimum number of individuals because of the fragmentary nature of the midden and the difficulty of assigning meaningful counts to the species present in low densities (see Glassow 2000;Giovas 2009;contra Mason et al 1998contra Mason et al , 2000. We used the Shannon-Weaver function (Shannon and Weaver 1949) to calculate the taxonomic diversity of the assemblages from both shell and meat weights of all dietary shellfish species recovered.…”

Investigating shellfish deposition and landscape history at the Natia Beach site, Fiji

“…The results suggest that for each excavation level MNI and weight are strongly correlated and therefore provide comparable results. While MNI and weight measurements both have their strengths and weaknesses for shell analysts (see Mason et al 1998;Glassow 2000;Claassen 1998;, we have chosen to use MNI for the analyses in this study. While shell weights can be useful for certain types of analysis, they may be problematic when modeling the potential impact of predation on populations of prey species.…”