Distribution and habitat suitability of Threatened and Migratory Marine Species in Northern Australia
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.
The thin edge of the wedge: extremely high extinction risk in wedgefishes and giant guitarfishes
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.
Conservation of handfishes and their habitats – Final Report 2020
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.
Life history of the Critically Endangered largetooth sawfish: a compilation of data for population assessment and demographic modelling
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.