The shark-like rays of the family Rhinidae (wedgefishes) are one of the most threatened group of marine fishes globally. The poorly-known Clown Wedgefish Rhynchobatus cooki has historically only been recorded from fish markets in Singapore and Jakarta, Indonesia. Its natural geographic range has until now gone undocumented. Intentional searches of social media posts describing wedgefish catches in Indonesia and Malaysia revealed the first wild records of this Critically Endangered species. A total of six catch records from small-scale fisheries were located from Lingga and Singkep Islands in Indonesia (1 from 2015, 4 from 2019, 1 from 2020). It remains unknown if the species is a micro-endemic to this small area of the Malay Archipelago, or if it is wider ranging. These results demonstrate the utility of social media searches to identify biogeographic records of cryptic and data-poor species.

The conservation of threatened elasmobranchs in tropical regions is challenging due to high local reliance on aquatic and marine resources. Due primarily to fishing pressure, river sharks (Glyphis) and sawfishes (Pristidae) have experienced large population declines in the Indo-Pacific. Papua New Guinea (PNG) may offer a refuge for these species, as human population density is low, and river shark and sawfish populations are thought to persist. However, few data are available on these species in PNG, and risk posed by small-scale fishers is poorly understood. This study observed elasmobranch catches in small-scale fisheries in riverine and coastal environments in the East Sepik (northern region), Gulf, and Western Provinces (southern region) of PNG. Surveys were conducted over a period of weeks to months in each region, during the dry season across seven field trips from 2017 to 2020. We observed a total of 783 elasmobranchs encompassing 38 species from 10 families. River sharks made up 29.4% of observations in the southern region, while sawfishes made up 14.8 and 20.3% in the northern and southern regions, respectively. River sharks were commonly caught by small-scale fishers in lower riverine environments in southern PNG, while sawfishes were generally less common and mainly observed through dried rostra. The primary threat to river shark and sawfish populations is their capture by small-scale fishers targeting teleosts for swim bladder. Persisting populations of river sharks and sawfishes indicate that PNG is the second known nation with viable populations of multiple species in the Indo-Pacific. However, populations are declining or at high risk of decline, and fisheries management and conservation are required to realize the potential of PNG as a long-term refuge.

Determining the genetic diversity and differentiation among populations is a critical element of conservation biology, but for many aquatic, data-deficient species with small population sizes, this is not possible. Closely related species may therefore provide a model. For the first time, using over 4000 single-nucleotide polymorphism loci, we characterise the population genetic diversity and structure of one of the world’s rarest marine fish, the spotted handfish (Brachionichthys hirsutus), a species which is also a member of the most threatened marine bony fish family (Brachionichthyidae). Fin clips were taken from 170 live spotted handfish across seven disjunct sites within the only known estuary (in Tasmania, Australia) where multiple populations of the species are found. Spatially discrete populations clustered into three genetic groupings and a significant variance in allele frequencies among populations (overall F_ST = 0.043), even at the small scale of the estuary, was observed. Furthermore, low contemporary migration rate estimates suggest low genetic homogeneity between locations. Because of the low genetic connectivity, population clusters of spotted handfish within the estuary should be considered as separate conservation management units. This insight should be considered for management and conservation strategies of other data-deficient and threatened species in the family.

The North Marine Bioregion is home to a diversity of threatened and data-poor marine species. In the absence of critical data on species’ distributions, population connectivity, and essential habitat, decision-making to progress the current ‘Developing the North’ agenda has the potential to negatively impact Matters of National Environmental Significance. Data compiled across multiple sources were used to model and map the distribution of 16 priority Threatened and Migratory marine species. The objective of the project was to improve the current data-poor species distribution maps held by DAWE to assist with policy decisions for these species. We used a spatial distribution modelling approach based on presence data for these species from 121 spatial datasets and associated, remotely sensed environmental variables. The output is a series of distribution maps to enhance decision-makers’ ability to assess potential impacts of development proposals in Northern Australia under the EPBC Act.

Wedgefishes and giant guitarfishes have overtaken sawfishes as the most imperilled marine fish families globally, with all but one of the 16 species facing an extremely high risk of extinction through a combination of traits: limited biological productivity; presence in shallow waters overlapping with some of the most intense and increasing coastal fisheries in the world; and overexploitation in target and by-catch fisheries, driven by the need for animal protein and food security in coastal communities and the trade in meat and high-value fins. Two species with very restricted ranges, the clown wedgefish (Rhynchobatus cooki) of the Malay Archipelago and the false shark ray (Rhynchorhina mauritaniensis) of Mauritania, may be very close to extinction. Only the eyebrow wedgefish (Rhynchobatus palpebratus) is not assessed as Critically Endangered, with it occurring primarily in Australia where fishing pressure is low and some management measures are in place. Australia represents a ‘lifeboat’ for the three wedgefish and one giant guitarfish species occurring there. To conserve populations and permit recovery, a suite of measures will be required that will need to include species protection, spatial management, by-catch mitigation, and harvest and international trade management, all of which will be dependent on effective enforcement.

This final report covers conservation work for red and spotted handfishes during 2019-2020. For red handfish this includes monitoring of juveniles in the wild immediately after their release following captive-rearing. Juveniles were recorded on all three monitoring surveys post release, indicating initial success of this conservation strategy to bolster wild population numbers. This report includes investigation into sex-determination in adults using morphometrics and found a lack of clear separation between males and females, indicating that focus should be on other methods for non-destructive sex determination. 

For spotted handfish this report includes population dynamics from 22 years of monitoring and found that within the Derwent estuary, both genomics and population dynamics suggest a well-structured population, with local populations acting in isolation from each other, or small groups. There had been an overall decline in the Derwent estuary’s Spotted handfish population.

The largetooth sawfish Pristis pristis is a Critically Endangered, once widespread shark-like ray. The species is now extinct or severely depleted in many former parts of its range and is protected in some other range states where populations persist. The likelihood of collecting substantial new biological information is now low. Here, we review all available life history information on size, age and growth, reproductive biology, and demography as a resource for population assessment and demographic modelling. We also revisit a subset of historical data from the 1970s to examine the maternal size−litter size relationship. All available information on life history is derived from the Indo-West Pacific (i.e. northern Australia) and the Western Atlantic (i.e. Lake Nicaragua-Río San Juan system in Central America) subpopulations. P. pristis reaches a maximum size of at least 705 cm total length (TL), size-at-birth is 72−90 cm TL, female size-at-maturity is reached by 300 cm TL, male size-at-maturity is 280−300 cm TL, age-at-maturity is 8−10 yr, longevity is 30−36 yr, litter size range is 1−20 (mean of 7.3 in Lake Nicaragua), and reproductive periodicity is suspected to be biennial in Lake Nicaragua (Western Atlantic) but annual in Australia (Indo-West Pacific). There was a weak relationship between litter size and maternal size in Lake Nicaragua, and lifetime reproductive output for an individual female from Lake Nicaragua was estimated as 73 pups. Future demographic models should aim to capture the variability and uncertainty in life history parameters for P. pristis and we encourage a conservative approach to any application for conservation and management.

A poster providing a summary of the Marine Biodiversity Hub research on the Northern River Shark.

A decade of Marine Biodiversity Hub Research led by Charles Darwin University shows the Northern River Shark to be more wide-ranging than previously thought, with new populations documented in several northern rivers. In 2010, the species was known from only 32 records in six rivers/estuaries; now more than 600 individuals have been recorded in 12 rivers/estuaries. Five genetically distinct populations were identified: four in Australia and one in Papua New Guinea. CSIRO close-kin mark-recapture analyses enabled the first population size estimates for one of these populations: the Northern Territory’s Van Diemen Gulf population size was estimated to be only ~600–1100 adults. The research provides monitoring and population assessment capability directly relevant to managing the recovery of the Northern River Shark and underpins environmental assessments under the EPBC Act in the context of northern Australia’s development.