Inundation, Extinction and Lacustrine Lives

In 1972 Lake Pedder in south-west Tasmania was submerged under 15 metres of water as a result of the Tasmanian State Government’s Middle Gordon Hydro-electric Power Scheme. The lake was subsumed into a much larger artificial impoundment formed by three rockfill dams, making it the largest freshwater lake in Australia. The Tasmanian government transferred the name Lake Pedder to the new impoundment. Three species endemic to the original Lake Pedder were recorded as extinct as a consequence of the lake’s flooding. The Lake Pedder planarian, a species of carnivorous flatworm, the Lake Pedder earthworm, and the Pedder galaxias, a small freshwater fish, disappeared from the lake area after the inundation of this unique habitat, the site of a number of ecologically valuable faunal communities. The divergent fates of these animals, their status as lost species and their significance as creatures both meaningful and meaning-making, marks out an extinction matrix suggesting that the absence of specific animals and specific experiences and ways of life matter more than others, that specific deaths can be more readily incorporated into stories of loss and restoration, and that the perceived malleability of habitats invariably involves death inscribed as sacrifice or justifiable casualties. This paper seeks to retrieve some of the perspectives and experiences forgotten or written over in the lake’s stories of flooding and redemption.

Extinct habitat, extant species: lessons learned from conservation recovery actions for the Pedder galaxias (Galaxias pedderensis) in south-west Tasmania, Australia

The Pedder galaxias (Galaxias pedderensis) from Lake Pedder, Tasmania, Australia, is one of the world’s most threatened freshwater fish. The flooding of Lake Pedder in 1972 for hydroelectric power generation caused a major change to the ecosystem that initiated an irreversible decline in the Pedder galaxias within its natural range. The flooding inundated another headwater catchment and native and introduced fish from this catchment colonised the impoundment. Numbers of the Pedder galaxias declined markedly as the impoundment matured and as colonising fish proliferated. Surveys in the 1980s confirmed the parlous state of the population, highlighting the need for conservation intervention. Several urgent conservation actions were undertaken to save the species from extinction. Translocation was considered the most important recovery action, given the critically low numbers in the wild. The species is now extinct from its natural range and is known from only two translocated populations. The conservation program, and specifically the translocation recovery action, saved the Pedder galaxias from extinction. The conservation management was extremely challenging since rapidly declining fish numbers needed timely and critical decisions to underpin the future of the fish. Recommendations are provided arising from this case study to guide conservation of freshwater fish in similar circumstances.

Two new species of Colubotelson Nicholls, 1944 in Tasmania's Lake Pedder: persistence of Phreatoicidae (Crustacea, Isopoda) in therein

The Tasmanian lakes Pedder and Edgar were inundated in 1972 to create a reservoir to feed into a hydroelectric powerscheme, despite biologists highlighting the uniqueness of the fauna therein. This fauna included undescribed species ofphreatoicidean isopods, which were noted in several subsequent publications but not formally described. In 2010, the orig-inal beds of these two lakes were revisited and successfully sampled for these isopods as part of a program to assess theconservation status of the unique fauna of this large freshwater body. These two previously reported species of phreatoi-cidean are both new to science, distinct from each other and belong to the genus Colubotelson Nicholls, so we providedescriptions and illustrations of these species to assist their identification by other biologists. The two species are easilyidentified by the shape of the pleotelson and setation of the head, although they are separated by considerably more thantwo hundred specific differences. C. pedderensis sp. nov. was collected only from the now deeply submerged bed of theoriginal Lake Pedder, whereas C. edgarensis sp. nov. may be found more widely in the current extent of Lake Pedder,owing to its appearance in previously collected samples from the original Lake Pedder as well as in the now drowned areaof Lake Edgar. These results bring the known diversity of the family Phreatoicidae in Tasmania to 26 described species,including 16 in the genus Colubotelson. The persistence of phreatoicids in Lake Pedder, despite the extensive changes to its ecosystem, suggests that these two species are more resilient than was suspected.