Research
White sharks
New insights into white shark movements in Australia
In Australia, white sharks have been recorded from central Queensland
to North West Cape in Western Australia, but they most commonly
are found in southern waters. Scientists at CSIRO Marine and Atmospheric
Research (CMAR) are using a range of tag types to learn more about
these movement patterns and the links between populations.
The broad-scale movements of white sharks tagged in southern Australia
suggest the population mixes across their Australian range, as well as
across the Tasman Sea to New Zealand. It confirms research findings in
other parts of the world that white sharks also sometimes swim in the
open ocean and can cross ocean basins, on occasion swimming at depths
exceeding 500 metres. The purpose of their deep-water forays is unknown.
Seasonal patterns
White sharks appear to move up eastern and Western Australia on a seasonal
basis but the timing varies between the two coasts. They move up the east
coast in autumn-winter to areas as far north as central Queensland and
then return south during spring.
In the west, they move up the coast as far as North West Cape during
spring and appear to return during the summer. It is not known what percentage
of the population undertake these migrations, but many of these same sharks
probably spend at least some of the year in South Australian waters, particularly
in the Great Australian Bight.
Similar seasonal movements are reported for white sharks in Californian
and African waters.
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Temporary residency and travelling periods
Sharks do not appear to reside permanently in one area. All the white
sharks tagged to date have shown either extensive movement away from the
tagging location, or at least limited patterns of residency. The sharks
may visit an area for a limited period - ranging from days to months
- then move on to other areas.
Some sharks tagged at the Neptunes, off Port Lincoln in South Australia,
have revisited at the same time of year on consecutive years. This has
happened for sharks visiting in both summer and winter.
The satellite tagging program is starting to shed light on where these
white sharks go when they leave the Neptunes. The movements have been
extensive, covering thousands of kilometres, and seem highly directed.
They move steadily from one site to another, sometimes hundreds or thousands
of kilometres apart, at a steady speed of about 3 km per hour. Then they
will suddenly stop for periods of days to months.
Why white sharks move this way remains a mystery, as does how they navigate.
Undoubtedly their movements revolve around the availability of food, or,
in the case of mature sharks, to other biological requirements such as
reproduction.
Prolonged, highly directional swimming when travelling between areas
also has been reported during tracking studies on blue sharks, mako sharks,
hammerhead sharks, tiger sharks and whale sharks.
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Common 'highways'
CMAR scientists have noticed some similarities in the tracks taken by
white sharks in Australian waters that suggest these sharks may follow
common routes or 'highways'.
Consistency of paths, or at least consistency of destination, between
sharks travelling in the same region has been recorded during several
acoustic tracking studies on other species, particularly when moving between
coastal waters and offshore banks.
If white sharks use 'highways' to travel between regions, identifying
such routes may help to minimise undesirable interactions with humans
and reduce the incidental capture of white sharks by commercial fishers.
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Depth-swimming behaviour
Data from acoustic, archival and pop-off archival tags show that white
sharks have a range of swimming behaviours. Some patterns are more common
when sharks are in certain habitats and may be related to different hunting
strategies for different types of prey.
Sharks commonly swim in shallow water during the day and in deeper water
at night when around seal colonies. This strategy probably helps them
to target seals, because white sharks have better vision during the day
than at night.
When in the shallow waters of Spencer Gulf or Gulf St Vincent in South
Australia, white sharks commonly swim along the bottom for prolonged periods,
probably because they are feeding on bottom dwelling fish and rays.
Travelling white sharks often show a very different behaviour, cycling
regularly between the surface and deeper waters. This yo-yo type behaviour
may help them detect navigational cues. Environmental cues such as detection
of bottom depth, scents and geomagnetic and solar orientation have been
suggested by various researchers as navigation aids.
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Travels with white sharks off WA
The tagging of three white sharks near Doubtful Island last year has
provided the first detailed accounts of white shark movements off Western
Australia, highlighting their extensive coastal travels in Australian
waters.
Pop-up Archival Transmitting (PAT) tags were fitted to the white sharks
in May and October. The tags record swimming depth, water temperature
and light levels every 1-2 minutes for a set time period, after which
they detach from the shark, float to the surface and transmit these data
via satellite.
They are among a range of tag types used by CSIRO scientists to learn
more about the white shark's long-term movement patterns and the links
between populations. This understanding will help address questions such
as, how far, how fast and how frequently white sharks travel, and whether
their movement patterns can be predicted.
White sharks are found across the world's temperate oceans, and concern
surrounds their numbers worldwide. They are protected in South Africa,
California, Florida, the Maldives, the Mediterranean Sea, Namibia, Malta
and Australia.
In Australia, white sharks have been recorded from central Queensland
to North West Cape in WA, with most found in southern waters. CSIRO tagging
studies suggest that white sharks in WA and South Australia are part of
a common population.
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Tagging tracks
The three sharks tagged near Doubtful Island ranged from 2.8-3.5 metres
in length and were all female. A researcher using a tagging pole attached
the PAT tags near the base of the dorsal fin via a short nylon tether
as the shark swam past the vessel.
Although two of the tags released earlier than planned, the following
movements were recorded.
All three white sharks moved rapidly to the west after being tagged,
indicating they were en-route through the tagging locations. Previous
tracking has shown that some sharks may pass rapidly through an area,
despite an apparent abundance of food, before taking up temporary residency
elsewhere. The reasons for this are unclear.
For the most part, the white sharks remained in coastal waters, but
one was particularly adventurous, travelling 5000 kilometres in 114 days,
up the coast to North West Cape then returning to near Doubtful Island.
This shark also travelled offshore into open ocean waters on at least
nine occasions, and made dives down to 570 metres, the deepest recorded
for a white shark in Australian waters. The reason for this offshore movement
remains a mystery, though open ocean movements of white sharks have been
reported elsewhere.
Two of the shark tracks provided the first direct evidence of white
sharks migrating north along the WA coast. Both sharks rounded Cape Leeuwin
and headed north along the coast in mid-late October reaching the vicinity
of Shark Bay by early November.
The cues for these movements, and the advantages of these long distance
travels, are unclear. Both sharks were sub-adult and their movements may
be associated with the availability of prey.
White sharks seasonally migrate along the eastern Australian seaboard
during autumn-winter and return down that coast in spring. The movement
north coincides with the spawning migrations of several fish species including
Australian salmon, tailor and sea mullet.
This tagging work was supported by the Aquarium of Western Australia
Research Foundation and Channel Nine Perth. Australian Geographic supported
one of the tagging trips. All tagging was carried out under permits from
Primary Industries and Resources South Australia, Fisheries Western Australia,
Department of Conservation and Land Management and with Animal Ethics
Committee approvals.
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