Distribution and current state of freshwater mussel populations (Kāeo, Kākahi) in wadeable Waikato streams

Report: TR 2022/01

Authors: Michele Melchior, Alicia Williams, Mark Hamer, Michael Pingram, Nicole Squires and Kevin Collier

Freshwater mussels are ecosystem engineers that are increasingly recognised for the many functional roles they play in streams, rivers and lakes, especially where they occur at high densities.

Despite their ecological importance, freshwater mussels are one of the most rapidly declining faunal groups in the world, and New Zealand species are not exempt. Declines have been attributed to a wide range of activities including river damming and other habitat modifications, loss of native fish species, introductions of non-native species, as well as toxic pollution and increased nutrient loading.

The Waikato region has two species of threatened mussel which can occur together in wadeable streams – Echyridella menziesii and the rare Echyridella aucklandica. An understanding of the distribution, abundance, size-frequency associations and habitat requirements of these sedentary, long-lived organisms is important to provide insights into the status of populations across the region and aid in both species’ conservation and management.

Waikato Regional Council recently developed a standardised protocol for monitoring mussels in wadeable streams and rivers. This protocol has been used here to report on the results of quantitative mussel surveys from 120 Waikato stream sites across six sub catchments. The surveys were undertaken by Waikato Regional Council in collaboration with the University of Waikato.