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Estuary perch (Percalates colonorum) are a long-lived and slow-growing species which are distributed throughout southeastern Australian estuaries. In Tasmania, only one known population remains which is located in the Arthur River, on the remote northwest coast. Tasmania is the only Australian state to list estuary perch as a wholly protected species (recreational and commercial), while other populations across their mainland distribution appear to be robust. A survey undertaken on estuary perch in the Arthur River in 2014–2015 indicated that the population was small (825–2375 fish) and dominated by three age classes between 12 and 14 years old. This population also has extremely low genetic diversity and is genetically distinct to mainland populations due to its geographic isolation. During a re-survey in December 2023, 378 estuary perch were captured, with 191 tagged and released, and 31 fish retained for age and gonad analysis. Although three strong age classes were detected (five, eight and twenty-three years), numerous weak and missing cohorts were apparent. This study also confirms this population has a delayed spawning season in comparison to mainland populations, with growth models and tag recaptures (32 fish) demonstrating a very slow but sexually dimorphic growth rate. By combining the datasets of the 2014/15 and 2023 survey, we present an updated understanding of the biology and population dynamics of this unique Tasmanian population, which has previously never been published. The results confirm the population is still reproductively active and stable; however, due to their restricted distribution, variable recruitment, slow growth, and small population, further conservation efforts are still required. Further legislative listings at both the state and federal levels are possible, which if progressed could provide additional protection and assist in applications for external funding and resources. This will support the development of a recovery plan which will consider re-stocking efforts and re-establishment of previously inhabited waters and investigate potential actions to improve the genetics of the Tasmanian population. Additionally, educational campaigns to inform the public and recreational fishers on the status of estuary perch in Tasmania will be undertaken.

Eradications of invasive species are usually expensive and difficult to conduct. Knowing when to declare an eradication successful requires distinguishing between failed detection of the target species due to imperfect sensitivity of the detection method and true species absence. This is difficult because the sensitivities of many detection methods are unknown. Environmental DNA (eDNA) methods can be used to detect species by analysing DNA present in environmental samples. eDNA has been promoted as a particularly sensitive and cost‐effective way to detect species at low densities and, importantly, the sensitivity of eDNA surveys can be quantified. Nevertheless, the effort and costs involved in detecting species at extremely low densities, such as required during eradication, have not been previously calculated. We evaluated the sensitivity of eDNA surveys in detecting the invasive European carp, Cyprinus carpio, in two lakes in Tasmania, Australia, one in which carp have been eradicated and a second in which carp are currently being eradicated. We determined the sampling effort and associated cost required to detect the species at very low density in these lakes. While our eDNA survey detected the current low density carp population present in Lake Sorell, we show that an exponential increase in sampling effort and associated cost will be required to confidently detect the species as the population declines. Similarly, while our eDNA survey corroborated the species absence from Lake Crescent, our detection confidence was low. We quantify the survey effort and financial investment required to confidently establish eradication success in Lake Crescent. Synthesis and applications. Estimating the environmental DNA (eDNA) survey effort and cost required to detect species at a given density will enable practitioners to make informed decisions on the feasibility of implementing such surveys. Quantifying the sensitivity of eDNA surveys will also inform the confidence practitioners should place in eDNA detection results to ensure appropriate management actions are implemented and provide a suitable stopping point at which to confidently declare eradication success. Estimating the environmental DNA (eDNA) survey effort and cost required to detect species at a given density will enable practitioners to make informed decisions on the feasibility of implementing such surveys. Quantifying the sensitivity of eDNA surveys will also inform the confidence practitioners should place in the results of eDNA detection surveys to ensure appropriate management actions are implemented and provide a suitable stopping point at which to confidently declare eradication success.

Common carp (Cyprinus carpio, L. 1758) are the most abundant pest fish species in Australia, detrimental to ecosystem integrity and values, and in need of suitable management solutions. In January 1995, this destructive pest was discovered in two large, connected Tasmanian lakes—Lakes Crescent (23 km2) and Sorell (54 km2). After an initial assessment, carp were immediately contained to these waters using screens to prevent their escape down-stream, followed by swift legislation to enforce closure of the lakes to the public. Assessment and evaluation of carp numbers occurred throughout the eradication program, with effort focused on Lake Crescent. Beginning with undirected removal, techniques progressively evolved to more sophisticated targeted removal with assistance from biotelemetry, in conjunction with gill netting and electro-fishing. Real-time population estimates and in situ observations resulted in a detailed cumulative understanding of carp population dynamics, behaviour and seasonal habitat choice. This allowed strategic deployment of fences to block access to marshes, and the installation of steel traps within the fences. These gears specifically prevented spawning opportunities, while concurrently capturing mature fish. Following 12 years of adaptive and integrated effort, 7797 carp (fry, juvenile and adult) were captured from Lake Crescent, with the last carp being caught in December 2007. The subsequent 14 years of monitoring has not resulted in the capture of any carp, confirming the successful eradication of carp from Lake Crescent. These management practices have been successfully replicated in the larger Lake Sorell, where 41,499 carp (fry, juvenile and adult) have been removed. It is now estimated that there are few, if any carp remaining. Collectively, the techniques and strategies described here were reliable, and can be applied as a model to control or eradicate pest populations of carp in freshwater lakes elsewhere.

Lampreys are jawless fishes (Cyclostomata) that are distributed antitropically around the world. Of the three extant lamprey clades (Petromyzontidae, Geotriidae, and Mordaciidae), Geotriidae and Mordaciidae are only found in the Southern Hemisphere. Geotriidae includes two anadromous species, G. australis and G. macrostoma, while Mordaciidae includes three species: Mordacia mordax (anadromous), M. lapicida (anadromous), and M. praecox (resident and non-feeding). Similar to several Northern Hemisphere species, Southern Hemisphere species are targeted by fisheries (G. australis), culturally significant (to Māori and Mapuche), key prey for many species (including endangered species), and regarded as crucial links for understanding the evolution of vertebrates. Prior to this work, key information on the Southern Hemisphere lampreys was dispersed throughout the literature, hindering attempts to synthesise critical information about these species. Here we provide detailed descriptions of the five Southern Hemisphere species to facilitate the identification efforts by technicians, managers, researchers, and other interested parties. We then review the taxonomy, distribution, biology, genetics, significance, and threats to these lampreys from over 100 years of written sources (e.g., peer-reviewed publications and agency reports), complemented by interviews and Indigenous knowledge, in order to synthesise and centralise key information. We conclude by identifying Western science knowledge gaps and offering suggestions for addressing them: this is critical as anthropogenic environmental changes are negatively affecting Southern Hemisphere lampreys, and will likely continue to do so into the future.

Species invading non‐native habitats can cause irreversible environmental damage and economic harm. Yet, how introduced species become widespread invaders remains poorly understood. Adaptation within native‐range habitats and rapid adaptation to new environments may both influence invasion success. Here, we examine these hypotheses using 7058 SNPs from 36 native, 40 introduced and 19 farmed populations of tench, a fish native to Eurasia. We examined genetic structure among these populations and accounted for long‐term evolutionary history within the native range to assess whether introduced populations exhibited lower genetic diversity than native populations. Subsequent to infer genotype–environment correlations within native‐range habitats, we assessed whether adaptation to native environments may have shaped the success of some introduced populations. At the broad scale, two glacial refugia contributed to the ancestry and genomic diversity of tench. However, native, introduced and farmed populations of admixed origin exhibited up to 10‐fold more genetic diversity (i.e., observed heterozygosity, expected heterozygosity and allelic richness) compared to populations with predominantly single‐source ancestry. The effects of introduction to a new location were also apparent as introduced populations exhibited fewer private alleles (mean = 9.9 and 18.9 private alleles in introduced and native populations, respectively) and higher population‐specific Fst compared to native populations, highlighting their distinctiveness relative to the pool of allelic frequencies across tench populations. Finally, introduced populations with varying levels of genetic variation and similar genetic compositions have become established and persisted under strikingly different climatic and ecological conditions. Our results suggest that lack of prior adaptation and low genetic variation may not consistently hinder the success of introduced populations for species with a demonstrated ability to expand their native range.

Investigating predator–prey relationships is an important component for identifying and understanding the factors that influence the structure and function of ecosystems. Mesopredators, defined as mid-level predators, have a profound effect on ecosystem structure by contributing an important link between apex predators and lower trophic levels. The diet of two elasmobranch mesopredators, Squalus acanthias and Mustelus antarcticus, was investigated in three locations in south-east Tasmania. Squalus acanthias consumed predominantly pelagic teleosts and cephalopods, while M. antarcticus predominantly consumed benthic crustaceans. As a result, there was low dietary and niche overlap between the two species. There was however evidence of intra-specific dietary variations between locations for both the species. This study has contributed to a better understanding of the top-down dynamics of the food web in coastal Tasmania, by providing important dietary information of two abundant mesopredators. In addition, the similar dietary patterns for S. acanthias and other Mustelus species over much of their global range suggest they may be consistent in their trophic roles across systems, with limited competition between these two sympatric mesopredators to be expected.

Trophic studies are key components in animal ecology and fisheries research. Although stomach samples are often obtained from fisheries, diet studies that consider the influence of fisheries on dietary results are still lacking. Here, the diet of the draughtboard shark Cephaloscyllium laticeps, an abundant mesopredator in Tasmanian waters, was investigated. Stomach samples were obtained from gillnet and craypot fisheries sourced from 4 regions: central (100% gillnet), east coast (63% gillnet, 37% craypot), northwest (100% gillnet), and southwest Tasmania (100% craypot). Overall, C. laticeps consumed the same prey types in all regions, but the importance of some prey varied significantly between regions. Generalized linear models showed that region was the main factor affecting prey abundance in the diet. Fishing method had some influence on the abundance of some prey (crabs, octopus, and other molluscs (gastropods and bivalves)), but the effect of fishing method on pot-related species such as Jasus edwardsii (lobster) and octopus was not as prevalent as expected. The common occurrence of C. laticeps as a bycatch species and its high consumption of targeted fishery species (lobsters and octopus) indicates that C. laticeps has a strong interaction with the fisheries. Therefore, the relationship between these fishery species and C. laticeps should be considered in food web studies in Tasmanian waters.

The diet of the broadnose sevengill sharkNotorynchus cepedianuswas investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance:Mustelus antarcticuswas the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly,Squalus acanthiaswas an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates ofN. cepedianusand elasmobranch prey, in particularM. antarcticusover 3 years coincided with declines in dietary occurrence ofM. antarcticus. Also,N. cepedianusandM. antarcticusabundances were both higher in Norfolk Bay than the Derwent Estuary. The correlation with diet and estimations of predator and prey relative abundance suggestsN. cepedianusmay move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.

Shark bites are of high public concern globally. Information on shark occurrence and behaviour, and of the effects of human behaviours, can help understand the drivers of shark‐human interactions. In Australia, a number of shark bite clusters occurred over the last decade. One of these took place in Cid Harbour the Whitsundays, Queensland, a region for which little was known about the shark community. Here, we describe and evaluate the research in response to that shark bite cluster. Fishing methods, acoustic and satellite tracking, and baited remote underwater video cameras (BRUVs) were used to identify the shark species using Cid Harbour, estimate relative abundance, and describe habitat use and residency. Side‐scan sonar and BRUVs were also used to assess prey availability. Recreational users were surveyed to understand human behaviour and their awareness and perceptions of ‘Shark Smart’ behaviours. This allowed shark occurrence and behaviour to be interpreted in the context of human behaviours in the Harbour. Eleven shark species were identified. Relative abundance was not unusually high, and residency in Cid Harbour was typically low. For example, 79% of acoustically tagged sharks visited the harbour on <10% days at liberty. Shark prey was available year‐round. Notably, anchored boats regularly conduct activities that can attract sharks (dumping food scraps, provisioning and cleaning fish). Alone, the methods used in this study had variable success, but combined they provided a large amount of complementary information. Including a social science component in the research response to the shark bite incidents allowed for a more holistic understanding of the Cid Harbour bite incidents. This study did not identify anything unusual about the shark community that could have contributed to the Cid Harbour shark bite cluster. However, the three incidents involved people bitten almost instantly after entering the water, which is unusual and suggests that feeding/attracting sharks to boats could have been a contributor and also that any species capable of biting humans could have been responsible. The eradication of activities that attract sharks to areas where people enter the water may reduce shark bite risk. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.

The bluntnose sixgill shark Hexanchus griseus, predominately a deep-water species (maximum depth: 2500 m), was captured approximately 30 km up a river on a bottom-set longline. Although this species has previously been reported moving into shallow waters at night in other regions of the world, this is the first confirmed report of a sixgill shark in a river.