Exotic frog incursion Limnodynastes dumerilii is an Australian frog exotic to New Zealand. It is an Notification of incursion aggressive coloniser and a In mid-October 1999 a member of the public took some unusual potential threat to New Zealand tadpoles to the Auckland Museum for identification, saying they had invertebrates and small been reared from a foamy egg-mass found in mid-August in a small vertebrates. A delimiting survey forested stream in the southern Waitakere Ranges. Once occurred in response to an metamorphosed, the tadpoles were identified as belonging to the incursion of the frog in Australian family Myobatrachidae – probably a species of Limnodynastes. Limnodynastes are exotic to New Zealand and their November 1999. presence was regarded as a biosecurity threat due to their predatory Tony Whitaker, co-author nature and their ability to rapidly colonise a variety of habitats. In during the day for egg-masses, tadpoles and frogs, and at night for the Waitakere Ranges they swere considered a particular threat to frogs and the sound of their highly distinctive ‘bonk’ call. Playback native Hochstetter’s Frogs (Leiopelma hochstetteri). tapes of calls were used to try to elicit a response. The survey covered The investigation, and identification all five catchments of the Waitakere Ranges (Fig. 1) During this period a consultant specialist(b) on Myobatrachid frogs arrived from At the home of the informant, were 15 outdoor aquaria containing Australia to advise on the ecology and reproductive cycles of several thousand tadpoles at various stages of development. These L. dumerilii and to comment on the suitability of the habitat in the appeared to be all of the same species and were said to have been Waitakere Ranges and west Auckland for establishment of this raised from the single egg-mass collected in August. At the site in the species. No further populations of L. dumerilii were located. Waitakere Ranges where the egg mass was found, there were tadpoles and two metamorphlings. The original site was examined closely by a group of herpetologists with the intention of mapping the extent of the exotic frog From these, a presumptive identification of Limnodynastes, probably incursion. However, no more Limnodynastes were found at either the L dumerilii, was made. This was confirmed by Australian original site or in adjacent catchments. Exceptionally high rainfall herpetologists after digital images of tadpoles and metamorphlings, early in November seemed likely to have destroyed any L. dumerilii followed by preserved specimens, were sent to Adelaide. There are tadpoles that might otherwise have been present. five subspecies of L dumerilii, and each has a different ecology and life history, with implications for likely place of origin, risk Eradication of the frogs assessment and control of the incursion. Four metamorphlings were Captive frogs: All known captive populations of Limnodynastes were therefore sent to an expert(a) , who had recently completed a eradicated. Vegetation and detritus were removed from aquaria, molecular phylogeny of the genus Limnodynastes using mtDNA. sealed in plastic bags and incinerated. All tadpoles that could Analyses clearly showed that the taxon in this case was L. dumerilii practicably be removed from tanks (>90%) were humanely killed by grayi, from coastal New South Wales (NSW). freezing, and any remaining tadpoles were killed by acidifying the water by addition of hydrochloric acid (33% at 10ml/litre). The tanks were then left for two hours before sterilisation for 2–3 days with sodium hypochlorite (12.5% at 20ml/litre). Frogs in the wild: In the preliminary survey Limnodynastes tadpoles were found in only two pools, both in the same stream and approximately 30m apart. All tadpoles seen in the upstream pool – the site where the egg-mass was allegedly collected – were removed and destroyed, as were two metamorphlings collected beneath stream-side vegetation. At the lower pool, most of the 20 or so tadpoles present escaped into deep mud when disturbed. The day after the visit torrential rain in the Waitakere Ranges caused widespread and serious flooding. When the stream was checked immediately following this storm the watercourse had been extensively modified and there was no evidence that any tadpoles Limnodynastes dumerilii - the Eastern Banjo Frog had survived. Nonetheless undetected adult frogs could have been A delimiting survey of the Waitakere Ranges was undertaken early in present in the area, or some metamorphlings could have dispersed November, in which suitable habitats for L. dumerilii were searched from the site. page 12 Surveillance 27(2) 2000 Extent of the incursion in the Waitakere Ranges and the known ecology and breeding The delimiting survey, the site survey and public response to biology of the species in its natural range. These facts suggested that widespread media coverage produced no evidence that L dumerilii the egg-mass had been placed at the site soon before discovery. was present beyond the original site in the southern Waitakere Potential for establishment Ranges, or that any still existed at the original site. L dumerilii was, therefore, found in the wild at just a single location. The original The natural range of L. d. grayi is coastal NSW, where it occupies a egg-mass had been hatched in uncovered, outdoor aquaria, and wide range of habitats and breeds in wetlands, ponds, and dams. some tadpoles had been distributed to other aquaculturists in urban The species could theoretically establish in parts of New Zealand. Auckland. These were recalled, but when the investigation began the The temperature, rainfall and relative humidity in Northland, first tadpoles had just metamorphosed and there remained a slight Auckland and parts of Coromandel, for example, are similar to those risk that a few metamorphlings may have dispersed from these tanks in coastal NSW. into the wild. Potential biological threats Origin of the incursion The main biological threats from this incursion were predation and The biology, ecology and behaviour of L dumerilii strongly suggested the introduction of chytrid fungi. L dumerilii is an aggressive that the population in the Waitakere Ranges was not the result of predator, presenting unacceptable risks to indigenous invertebrates dispersal from elsewhere in the region. The habitat in the southern and small vertebrates, including native frogs (Leiopelma spp.) and Waitakere Ranges is unsuitable for the maintenance of a viable wild skink species. L dumerilii also is one of the frog species known to population of Limnodynastes unsupported by immigration from carry chytrid fungi – a key factor implicated in amphibian decline in elsewhere in the district. The species is conspicuous because of its other countries – and it has itself suffered major fungal-related loud and characteristic call and because it usually congregates in mortalities in parts of Australia. No diseased or dying Limnodynastes pools to breed. It also breeds prolifically and occupies a wide range tadpoles or metamorphlings were found during this investigation. (3) of habitats. An established population in the area should therefore Nonetheless, the potential for Limnodynastes infection did exist . have already been detected. The original site was remote from the Monitoring programme usual accidental entry points (e.g. ports, freight yards). There were also serious discrepancies between the details surrounding the find The fact that tadpoles had been found at the original site in the Waitakere Ranges in November, and that an egg-mass had allegedly been laid there in mid-August, meant that at least a pair of adult frogs could theoretically have been present in the area and that some metamorphlings could have dispersed before flooding at the site. Monitoring of the site is therefore needed for a period of at least two years(4). The two most obvious and characteristic features of L dumerilii are its loud banjo-like call and its distinctive foamy egg-masses. These features are the focus of a two-pronged monitoring programme centred around potential breeding sites and scheduled to run until at least November 2001, and supplemented by a publicity campaign. If signs of frogs are detected, intensive site surveys would occur. • If any L dumerilii remain in the Waitakere Ranges their population density would likely be very low and consist mainly of young animals. Males do not begin calling until they reach adult size (>50mm SVL), usually at 2 years of age, so calling in the first year would probably be sporadic if it occured at all. Thus, the most cost- effective way of detecting the frogs by their calls is by use of remote recording devices. Several recorders will be installed at the original site and in adjacent catchments in April 2000, and will operate throughout the spring and autumn breeding seasons. This equipment plays a single call, followed by 5 seconds of recording to detect a response, repeated every 15 seconds during the three hours after dusk. In addition, field staff will listen at key locations at night during the height of the breeding season and when weather Fig 1: Waitakere Ranges - investigation sites parameters are optimum. page Surveillance 27(2) 2000 13 • At approximately fortnightly intervals between March–May and (4) Cogger HG.. Reptiles and amphibians of Australia. Reed, Chatswood NSW, August–November, field staff will visit potential breeding sites to pp775, 1992. search for the characteristic foamy egg-masses. These searches will (5) Hoser RT. Australian reptiles and frogs. Pierson, NSW, pp238, 1987. occur immediately after periods of high temperature (>20ºC) and (6) Martin AA. Studies in Australian Amphibia: III. The Limnodynastes dorsalis high rainfall, since these are the usual triggers for breeding. The complex (Anura: Leptodactylidae). Australian Journal of Zoology, 20, 165–211, foamy egg-masses laid by L d grayi are distinctive and highly visible. 1972. • A publicity campaign is planned for Spring 2000, and a fact sheet (7) Tocher M, Waldman B.