Size does matter: methodological comments on sieve size and species richness in fishbone assemblages

Vale and Gargett (J. Archaeol. Sci. 29 (2002) 57) discuss the finds from sieving experiments through 6 mm, 3 mm, and 1 mm mesh sizes from Arrawarra-I, a coastal midden site in Australia. They claimed that the relationship between sieve mesh size and both taxonomic richness and abundance is not straightforward. We reanalyzed Vale and Gargett's data to estimate species richness in larger sample sizes. By fitting logarithmic series to the data, we calculated the alpha diversity, and used that statistics to predict number of species expected at a given sample size. This statistical method is called “the equivalent alpha diversity method for abundifaction”. We demonstrate that taxonomic diversity would have been higher (14 species rather then 10) for an NISP of 2000 bones, sieved through a 1 mm mesh. We also demonstrate that Vale and Gargett's conclusion is flawed due to their small sample size (432 identified bones out of 60,000), inadequate sampling methods and poor analytical methodology. By using Vale and Gargett's data, we reach the opposite conclusion, and show that the use of 3 and 1 mm mesh sieves is indeed important in measuring diversity of archaeological assemblages in general, and of fish assemblages in particular.