Abstract
Freshwater biodiversity is facing a range of challenges worldwide. Threats such as introduced species, habitat degradation and a changing climate are drivers for extinction. Understanding species that are at risk from these threats is important to cataloguing biodiversity. Some freshwater species are especially difficult to protect and understand due to their cryptic nature, small populations or limited range data. This study addresses the distributions of range-restricted freshwater fishes in Aotearoa New Zealand using specimens from museums to inform historic distributions. The focus of this study is on the upland longjaw galaxias (Galaxias prognathus) and alpine galaxias (G. paucispondylus) populations that were recorded historically in the Maruia River and attempt to ascertain if the populations are still extant. The former population is particularly important as it is the only population of G. prognathus found west of the alpine divide and was located significantly further north than the current known range limits of this species. Investigation includes the relationships between these populations and their eastern counterparts. Electrofishing and environmental DNA surveys found no evidence of either target species throughout the catchment. Historical records confirm the location of sampling is likely to be correct, and additional specimens were discovered in museum collections in Museums Victoria. Detailed morphological examination showed significant morphological differentiation between the Maruia River G. prognathus and the extant populations in their known distribution. The morphological examinations also showed the singular G. paucispondylus specimen was incorrectly identified and is a large G. divergens which commonly occurs in the Maruia River. All ancient DNA approaches failed due to the preservation methods used for the Maruia River galaxiid specimens, and thus genetic analysis of phylogenetic relationships was not possible. The population of Maruia G. prognathus were found to likely represent an evolutionarily significant unit and represents a previously unknown loss of biodiversity. The museum specimens used in this study provided context for the historical distribution of G. prognathus and G. paucispondylus and demonstrates the usefulness of museum collections to study biodiversity.