Abstract
We measured δ 15 N, δ 13 C, and percent carbon (C) and nitrogen (N) on foot and remaining soft tissue of the two native freshwater mussel species Echyridella aucklandica and E. menziesii (Hyriidae: Unionida) from three Waikato, northern New Zealand, streams to investigate differences among sites, sexes and species. Mean differences in δ 15 N and δ 13 C between foot and remaining soft tissue (mainly guts, gills and gonads) were 15 N and δ 13 C displayed marked differences among sites for both species, with δ 15 N variations consistent with the level of catchment land‐use intensification. Variation in δ 13 C and δ 15 N among replicate mussels was low indicating few individuals are required to precisely characterise isotope signatures of local populations. The lack of evidence of trophic resource partitioning among species, and consistent differences in isotope ratios between sites, suggests that the more widespread and abundant E. menziesii may provide an effective baseline integrator of catchment activities that alter carbon supplies and nitrogen sources.