Early detection of biological invasions is critical to reducing their impact, but because invading organisms are initially at low densities, detection and eradication can be challenging. Here, we demonstrate the utility of faecal DNA analysis for the detection of an elusive invasive species -the red fox, Vulpes vulpes, which was illegally introduced to the island of Tasmania in the late 1990s. Foxes are a devastating pest to both wildlife and agriculture on the Australian mainland, and would have a similarly serious impact in Tasmania if they became established. Attempts to eradicate foxes from Tasmania have been hampered by unreliable distribution data derived mostly from public sightings. In response, we developed a highly accurate and reliable DNA-based PCR-multiplex test that identifies foxes from field-collected faeces. We also developed a sexing test, but it was reliable only for faeces less than three weeks old. Faeces are a useful target for DNA-based diagnostics in foxes because they are deposited in prominent locations and are long-lasting. The species identification test formed a key component of a Tasmania-wide detection and eradication program. In all, 1160 geo-referenced carnivore scats were analysed; of these, 78% contained DNA of sufficient quality for species identification. A single scat from the north-east of the island was identified as belonging to fox, as was a nine-week-old roadkill carcass from the north coast, and a blood sample from near Hobart, triggering increased control and surveillance in these regions. The accuracy, reliability, and cost-effectiveness of non-invasive tests make them a critical adjunct to traditional tools for monitoring cryptic invasive species that are at low density in the early stages of invasion and when eradication is still an option.

Allozyme and mitochondrial DNA variation was surveyed in Acanthopagrus butcheri to examine the pattern of gene flow among estuaries in south-east Australia. Allozymes distinguished two peripheral estuaries from the remaining six, although the pattern of genetic variation could owe more to selection than reproductive isolation, and overall structure was small ( ¼ 0Á012). In contrast, mitochondrial DNA revealed a high degree of genetic structure ( ¼ 0Á263), and a significant relationship with geographic isolation. Consequently, contemporary gene flow mostly between adjacent estuaries, consistent with a one-dimensional stepping stone model, is evident in south-east Australia. The data indicate that management of A. butcheri within the study range should be conducted at the scale of individual or geographically proximate estuaries. # 2004 The Fisheries Society of the British Isles

An investigation of allozyme variation at 32 loci in the black bream, Acanthopagrus butcheri (Munro), and the yellowfin bream, Acanthopagrus australis (Günther), revealed heterozygosities (H) equal to 0.035 and 0.065, respectively, and polymorphism (P0.95) equal to 0.067 and 0.200, respectively. The genetic data confirm the very high level of genetic similarity previously found between the two species, but nevertheless also support their recognition as separate species. The finding of only limited allozyme differentiation at three polymorphic loci amongst six black bream samples from south‐eastern Australia is consistent with the existence of a single panmictic population in this region. This would require that adult black bream have a greater capacity to survive in near‐shore marine environments than previously realised and that dispersal between estuaries is more extensive than was shown by tagging studies. In contrast, significant differences were found at two loci between black bream from south‐eastern Australia and a sample from south‐western Australia. The degree of genetic divergence between stocks in south‐eastern and south‐western Australia suggests that only local brood stock should be used for aquaculture or re‐stocking as a precaution until further investigations with DNA‐based techniques are conducted. The genetic divergence detected supports separate management for populations in Western Australia and Victoria.