A Comparison of Quadrats Versus Timed Snorkel Searches for Assessing Freshwater Mussels

Abstract

Nine sites in the Neosho River (Kansas) were surveyed for unionid mussels during summer 1994 to compare the effectiveness of quadrat sampling vs. timed snorkel searches for evaluating relative abundance, species richness and diversity, size distribution and evidence of recruitment. At each site, timed snorkel searches were conducted in a 100-m stretch, 10-m wide, of wadable habitat. Mussels were returned to their original location following identification and sizing. Next, 40 1 m2 quadrats were sampled from the same stretch. Finally, 15 qualitative substrate samples (approximately 1 m2) were sieved in an attempt to detect recruitment. A total of 786 mussels were caught during 12 h, 11 min of snorkel searches compared to 896 mussels from 360 1-m2 quadrats. Quadrula metanevra was the most abundant species collected by either qualitative or quantitative methods. Differences in assessments of species diversity and relative abundance between methods were not significant; however, timed searches revealed significantly fewer species, and were less effective in detecting cryptic species than were quadrat samples. Little evidence of recent recruitment was detected in any of the methods. Quantitative methods are recommended for assessments of density, biomass, size demographics and local scale phenomena, whereas qualitative searches are more efficient when targeting large species or examining broad distributional patterns. However, some form of substrate sieving is necessary to detect small mussels.