Conserving the iconic and highly threatened mahseer fishes of South and Southeast Asia.

Abstract

This thesis and supporting papers constitute the submission for an award of a PhD research degree by publication and consists of a cohesive synthesis linking a total of eight published papers across seven peer review journals and an IUCN Red List assessment. The mahseers (Tor spp.) represent an iconic group of large-bodied cyprinid fishes found throughout the fast-flowing rivers of South and Southeast Asia. Due to the considerable religious, cultural and recreational significance of these fishes, and the anthropogenic pressures they face, they are of high conservation concern and represent flagship and umbrella focal species for the sustainable management of river systems throughout their biogeographic range. Based on research conducted since 2012, considerable advances in the taxonomic and human dimension aspects of mahseer conservation have been acheived. Engagement with the recreational angling community has demonstrated the high value, and future potential for this rapidly expanding stakeholder group to impact positively on the conservation of mahseer and rivers more generally. This has been evidenced through the development of economic incentivised community habitat protection initiatives. Specifically, community level recognition that a live fish captured and released by paying anglers has a renewable value over the single revenue value of a harvested fish, has been shown to offer employment opportunities and support the sustainable stewardship of aquatic ecosystems. Where such incentives are lacking however, fisheries continue to be subject to high levels of exploitation, due to limited alternative livelihood opportunities available within impoverished rural communities. Further, and due to a combined lack of political will and the difficulties associated with sampling large fishes in large and remote monsoonal rivers, records from catch-and- release angler logs have provided the only available insight to the temporal performance of mahseer populations. Over a 12 year period, angler derived data not only revealed a collapse (>90% reduction) in the River Cauvery’s endemic mahseer population, but also evidenced the establishment and rapid invasion of the non-indigenous blue-finned mahseer, thus highlighting the previously under-appreciated risks of stocking mahseer species into novel systems beyond their natural distribution range. With particular focus on the mahseers of South India’s River Cauvery, this work has afforded the largest of all mahseer species, the hump-backed mahseer, with a valid scientific name (Tor remadevii) and, through extensive analysis of angler catch data, has highlighted its high extinction risk, with it now assessed as ‘Critically Endangered’ on the IUCN Red List of Threatened Species. This has in turn impacted on regional and national fishery and wildlife policy and affected a concerted international effort to apply a multidisciplinary and multiple stakeholder approach to saving this iconic species of megafauna from extinction. In the absence of these works, it is highly probable that the species would have remained on a trajectory towards rapid extinction. Instead, the first major steps to safeguarding its future have been taken. In achieving these research highlights, this work has also resulted in an extensive gap analyses to identify and address some of the many knowledge gaps which have been constraining the effective direction and efficacy of international efforts to conserve species across the genus. With specific reference to previous taxonomic uncertainties, a comprehensive synthesises and critique of species descriptions and subsequent morphological and molecular focused literature, has resulted in the previously listed 24 species of Tor, being revised to just 16 valid species. Additional collation of available data to inform distribution ranges, population trends and threats across the genus, has facilitated the revision of IUCN Red List assessments, with one species now ‘Critically Endangered’, three as ‘Endangered’ one as ‘Vulnerable’, three as ‘Near Threatened’, and eight remaining ‘Data Deficient’. In discussing residual uncertainties, population threats, conservation prospects and the role of stakeholders across the region, this submission concludes with an overarching synthesis of the current knowledge base pertaining to the genus Tor. In discussing taxonomic clarifications, emerging research priorities and potential mechanisms to effect species conservation, this also represents a first point of reference for researchers, while encouraging further research to challenge and enhance the knowledge base necessary to conserve and promote these freshwater icons as focal species to support the ecological integrity of South Asian rivers.