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.