CANBERRA, Sept. 5 (Xinhua) -- Australia's critically endangered eastern grey nurse shark population is showing a slow but steady increase, research revealed on Friday.
The number of adults in the eastern grey nurse shark population is estimated to have increased by about 5 percent annually between 2017 and 2023, rising from about 1,096 to 1,420 adults, according to a statement from the National Environmental Science Program Marine and Coastal Hub, involving 28 research partners.
Scientists collected biopsy samples from over 300 grey nurse sharks off the coast in the Australian state of New South Wales (NSW), and analyzed their DNA to estimate population size based on family relationships, the statement said.
Despite a very small population with low genetic diversity, the slow growth of eastern grey nurse sharks indicates that conservation efforts, especially removing fishing threats at key breeding and feeding sites, are proving effective, it said.
Grey nurse sharks breed slowly, producing two pups every two years after a year-long gestation. They are also long-lived and slow growing, said David Harasti of NSW Department of Primary Industries and Regional Development (NSW DPIRD).
"This makes their recovery fragile, especially given the low levels of genetic diversity in the eastern population, which makes it vulnerable to even small environmental changes or disturbance from human activities," Harasti said.
The research used advanced genetics and statistical modeling called close-kin mark-recapture to identify the parents and genetic relationships between the sampled individuals to estimate the eastern grey nurse shark population, according to the Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia's national science agency, quoted by the statement.
A large number of related individuals means there are fewer adults, translating to a smaller population. Conversely, fewer related individuals means there are more adults, and a larger population, said the CSIRO, which led the research with the NSW DPIRD.
The grey nurse shark remains listed as Critically Endangered on Australia's east coast and is one of 110 priority species under the Australian government's Threatened Species Action Plan 2022-2032. ■
