Sciences · Prolifération en Australie-MéridionaleLa prolifération en Australie-Méridionale a laissé au moins 8,250 requins et raies morts. Les populations pourront-elles se reconstituer ?Rédigé 1 novembre 2026 à 20:04 UTCRegarderTranscription0:07Citizen scientists recorded at least eight two hundred and fifty dead sharks and0:10rays in bloom affected waters in South Australia.0:13Researchers warned some local populations may have collapsed.0:16Can surviving animals rebuild those populations, especially the rarest species?0:20Marine ecologist Janine Baker led the tally for the Great Southern Reef Foundation.0:24It draws on the South Australian Marine Mortality Event Citizen, science project on0:28iNaturalist, where people recorded dead marine animals.0:31The Foundation publicized the findings in October.0:33These losses built up during the bloom.0:36The reported losses include around four five hundred southern fiddler rays, eight0:40hundred and fifty Port Jackson sharks, and six hundred seventy wabagongs.0:43These are familiar animals living on or near the seafloor.0:46Many were recorded after their bodies washed ashore.0:49The foundation's minimum of eight two hundred and fifty is the more precise version0:52of the rounded figure: more than eight, two hundred.0:55Animals that died without being found or reported are missing.0:58The foundation says the true toll is likely higher.1:01But T here is no reliable estimate of how much higher.1:04The bloom spread far beyond one beach.1:06It developed in March2020,5 around the Fleury Peninsula near Adelaide.1:11It subsequently reached Yorke Peninsula, Kangaroo Island, Gulf St.1:14Vincent, and parts of Spencer Gulf.1:16Scientists identified a complex bloom that included Carenia cristata, an alga that1:20produces toxins called Bravitoxins.1:23The death tally records animals found in affected waters.1:26It doesn't tell us that every animal was individually tested for those toxins.1:29Toxin analyses found forms of brevitoxin that hadn't previously been reported in1:33Australian harmful algal blooms.1:35Scientists are also investigating whether bacteria and viruses influence how these1:39blooms develop.1:40Their possible roles are still being explored.1:42Charlie Huverniers, director of Flinders University's Marine and Coastal Research1:46Consortium, says this was probably the largest mass mortality ever recorded for1:50sharks and rays.1:51That's his assessment of its possible historical scale.1:53He's also concerned about animals his team tagged before the bloom.1:56Huvenir says none of more than one hundred and fifty tagged sharks and rays had2:00returned twelve months later.2:02His research concerns metropolitan populations of Port Jackson sharks and fiddler2:06rays.2:06Their absence adds another warning beyond the bodies found on beaches.2:10Those missing animals could have died, moved elsewhere, or gone undetected.2:14Earlier in February2026 , researchers were also investigating an apparent2:18disappearance of Port Jackson sharks after no eggs were found in the recent breeding2:22season.2:22That deepened concern about local reproduction.2:24Diver David Moorehead had completed around two zero dives in South Australian waters2:29before encountering a pygmy thornback skate early in the bloom.2:32He photographed it off Edithberg Jetty.2:34He'd never seen one before.2:36The skate is exceptionally rarely seen, with many encounters happening when fishing2:40trawlers bring one up.2:41Its small range lies mostly within affected South Australian waters.2:44Moorehead feared he could be witnessing the end of a species.2:47Scientists haven't confirmed an extinction.2:49The coastal stingery is considered endangered by the International Union for2:53Conservation of Nature.2:54Australia's federal threatened species list doesn't include it.2:57The pygmy thornback skate also lacks a federal threatened listing.3:00Those classifications use different assessment systems.3:03Huveners warns that animals with naturally small populations.3:06Or restricted ranges overlapping the bloom could face some level of extinction.3:10Most affected species have wider ranges extending into unaffected waters.3:14Those surviving populations offer a possible route back, while restricted range3:19species have fewer places to survive.3:21The federal government's two thousand and twenty six assessment cycle specifically3:25included species at risk from the bloom, but nobody nominated these two species.3:29Anyone can nominate a native species under the federal environment law.3:32A nomination needs scientific evidence about its population.3:35Too little information has held up that process.3:37The federal system has no data, deficient listing category.3:41When there isn't enough evidence to assess eligibility, a species is found3:44ineligible.3:45So an unlisted, poorly studied species can still be in danger.3:48Weirhead says many common bony fish and marine invertebrates are recovering, but he3:53recalls seeing only one ray since the bloom, swimming under the steppes at Second3:57Valley.3:57That's one experienced diver's observation, rather than a population survey.4:01Other ray sightings also offer hope, but they can't yet show whether breeding4:05populations are rebuilding.4:06Sustained monitoring will need to track abundance and reproduction, especially among4:10the rare species.4:11Sharks and rays generally mature slowly, reproduce infrequently and have small4:15litters.4:16Animals arriving from unaffected waters could become visible again well before local4:19populations regain their former numbers.Lire l’articleChronologie de l’histoireHeyDex
