Translocation of the threatened Growling Grass FrogLitoria raniformis: a case study

Abstract

Translocation is occasionally suggested as a last resort strategy for dealing with 'unavoidable' loss of Growling Grass Frog Litoria raniformis habitat in urbanising landscapes. However, examples of attempts to translocate an entire population of L.. raniformis are rare and their success (or lack of success) is poorly documented in the literature. In this study, we detail the translocation of a population of L.. raniformis from a farm dam being destroyed for residential development to a purpose-built wetland 480 m away. The population was translocated between November 2010 and May 2011. We used mark-recapture to estimate the number of frogs in the population prior to translocation. Visual counts of L.. raniformis at the dam indicated a maximum of 39 adult frogs to be present while 355 frogs were marked over the course of a single season (November 2010 to March 2011). Translocation of 156 frogs and unassisted colonisation by 32 frogs resulted in an estimated 70% of adults marked at the dam moving to the wetland and 91% of those remained there for the duration of the translocation study period. The population and two measures of habitat quality (aquatic vegetation cover and water quality) were monitored for three active seasons post-translocation. Successful breeding was demonstrated for the first year only. A decline in breeding success was attributed to a reduction in habitat quality at the wetland, particularly the loss of submergent and floating vegetation due to the presence of Common Yabby Cherax destructor, a species that did not occur originally in the dam. We believe that colonisation of the wetland by this crustacean was due to the wetland being constructed on-line. An attempt to control the C. destructor population and re-establish the aquatic vegetation was unsuccessful. We encourage the publication of all successes and failures in future attempts to establish translocated bell frog populations. If further experimental translocations have low success rates, then translocations should be reconsidered as a conservation strategy for L.. raniformis in urbanising landscapes and greater emphasis placed on in situ habitat protection.

Genetic structure and diversity of the endangered growling grass frog in a rapidly urbanizing region

“…There is currently no evidence that populations of L. raniformis can be successfully relocated [ 32 ]. Indeed, all translocation attempts for this species and the closely related L. aurea have failed or the focal populations are performing poorly [ 82 ], despite L. aurea being the subject of more translocation attempts than any other Australian frog [ 83 ].…”

Impacts of human‐induced environmental change in wetlands on aquatic animals

“…The time elapsed since habitat alteration may play an important role in how animal communities and populations are structured within wetland systems (Norton, Evans & Warren, 2016). For example, newly created wetlands can be initially colonised by the endangered growling grass frog Litoria raniformis, but populations often decline through time (Koehler, Gilmore & Newell, 2014). Such situations may be indicative of the presence of an ecological trap, particularly if these altered wetlands continually receive, but do not supply, migrants.…”