Science1 publisher2 min readPublished
Thirty years of tracking yielded usable movement data for eight of Australia's 29 shortlisted shark and ray species
University of Queensland researchers pooled three decades of tracking studies into the first cross-boundary connectivity baseline for Australian sharks and rays. Five of the eight species they could model turned up outside Australian waters.
The Scientist · Science desk
What happened
- University of Queensland researchers pooled 30 years of satellite tracking, acoustic and mark-recapture studies to map how migratory sharks and rays connect Australian waters with neighboring countries.
- Of the 29 species in Australian waters listed under the Convention on the Conservation of Migratory Species, 18 had no published movement information at all.
- Eight species carried enough data to support a network model, and five of those were documented crossing international borders.
- Tracked animals turned up as far away as South Africa, New Zealand, Indonesia and Micronesia, and in offshore waters beyond any national jurisdiction.
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Why it matters
- constraint The CMS listing implies management for all 29 species, and for the 18 without published tracks there is nothing to tell a manager which other country's fleet the animals actually meet.
- exposure Bezerra's whale shark example sets out the exposure plainly: full protection in Australian waters still leaves an animal reachable by fishing on the Indonesian leg of its route.
- decision The 21 unmodeled species now sit on a published list, which gives anyone deciding where the next satellite tags and acoustic receivers go a ranked starting point.
- capability For the eight modeled species, Australian agencies can point to named counterpart jurisdictions when they ask for cooperation on a stock.
The 18 species with nothing published are not a random draw from the list. Associate Professor Daniel Dunn [20] put the reason in physical terms. "One of the big problems we have is that these animals don't breathe air and don't regularly come to the surface, making them much harder to tag and detect," he said [9]. Birds, he said, are much easier to see and track and therefore have much more movement data available [10].
Eleven of the shortlisted species had something published about their movements [15]. Eight of those carried enough detail to build a network model [5], which leaves three species with records too sparse to model [16]. The models cover 28% of the shortlist [17].
Five species were documented crossing borders, and the denominator for that five is eight, not 29 [5]. Twenty-one species were never modeled [18]. For 18 of them, no published track exists that would show whether they leave Australian waters at all [4].
The five border-crossers, named in a paper in Conservation Biology [2], are whale sharks, blue sharks, shortfin mako sharks, school sharks and white sharks [6]. Doctoral candidate Diego Bezerra [20] said blue sharks and school sharks are particularly susceptible to being caught as bycatch [13]. "This allowed us to identify which species require international cooperation to support their recovery, and it exposed huge gaps in the available data," he said [14].
Dunn's argument for why the gaps matter to management is procedural. "You cannot manage migratory species by only looking at one part of their migration," he said [8].
Bezerra describes an asymmetry in capacity. "Australia does a relatively good job of protection, but other nations do not always have the same capacity to implement strong measures," he said [11]. "For example, whale sharks are protected here, but they migrate to Indonesia, where fishing could put them in danger" [12]. That comparison is his characterization of what the movements imply; the network models themselves output connections between jurisdictions, not fishing mortality in each one [1]. He also said it is important that Australia supports neighboring nations through collaboration and by sharing technology and information [19].
What to watch
- New tagging on any of the 18 species with no published movement data, especially if it lands in a jurisdiction Australia has no fisheries arrangement with.
- Whether CMS parties use the eight-species network to structure bilateral work with Indonesia, New Zealand or South Africa.
- Whether funders treat hard-to-detect species as a priority, which would test Dunn's tagging-difficulty explanation for the gaps.