Where do Great White Sharks go?

Dyer Island and Gansbaai, two names which were unknown to the world a decade ago… now names that have become famous worldwide, synonymous with the Great White Sharks.

Michael Scholl has identified over 800 different White Sharks at Dyer Island alone since 1997 using photographic identification. About 30% of these sharks have been subsequently observed, and 80 of these sharks have been observed for overall periods longer than one year. Some sharks come back every year during the same season, but none of the sharks around Dyer Island seems to be resident, and probably stay an average of only one to two weeks.

The question remains: Where are they going between visiting our area?

In 1997 – 1998, a group of scientists examined the DNA of white shark tissue samples collected in South Africa, Australia and New Zealand. The findings published in Nature in 2001 showed that male white sharks probably swim between South Africa and Australia, whereas females of the respective continent do not seem to mix.

From tagging and photographic identification programs, we know that white sharks do swim between False Bay, Dyer Island and Mossel Bay on a regular basis.

Two white sharks were tagged with Argos satellite tags in Australia in 2000 and 2001 respectively, and the second shark swam over 3000 km in less than four months. In a similar study conducted in California, four out of six white sharks tagged with PAT tags during 1999 – 2000 moved offshore after a short near-shore phase period. One of these sharks swam 3800 km to waters off the western coast of Hawaii. This study indicated that white sharks seem to have a much more extensive pelagic (deep sea) range than what was previously thought.

To answer similar questions in South Africa, a joint collaboration (www.SharkResearch.org) between Marine and Coastal Management (MCM), the Wildlife Conservation Society (WCS, www.WCS.org), the Universities of Cape Town and Pretoria, Natal Sharks Board and the South African Museum was initiated in 2002.

The White Shark Trust welcomed the joint team on board Lamnidae, the White Shark Trust research boat, to conduct the PAT tagging in August 2002, April 2003 and November 2003 for a two week period each.

There are two main types of satellite transmitters available to track the movements of marine animals: PAT and SPOT tags.

The PAT tag is a non-transmitting device which records and stores information for a preset period of time about the depth at which the shark is swimming, the ambient water temperature, and more importantly, the luminosity (available light). This device then detaches itself from the shark and floats to the surface, at which time it becomes active and transmits all the stored information via satellite to a computer. From the luminosity measurements, the tag will estimate sunrise and sunset times every day, from which it is then possible to estimate the location of the shark during its tagged phase. These locations are quite imprecise and will not tell us whether the shark was in False Bay or at Dyer Island, but we will know whether the shark was off Cape Town or off the Natal coastline. This type of tag is useful to investigate long-range movements of white sharks, but the main advantage is that the shark’s position, however imprecise, can be estimated for every day.
The second type of tag is the Argos SPOT transmitter, working in a similar way as a GPS device except it operates the opposite way. This device will emit signals and transmit information each time the tag’s antennae breaks the surface of the water. An array of satellites orbiting just above the earth atmosphere will estimate the position of the shark from these signals, and transmit the information back to a computer. This satellite tag is very useful to investigate precise movement patterns, but it is subject to the explicit condition that the shark comes to the surface, as radio frequencies cannot transmit through water.
During August 2002, eight satellite tags (4 PAT and 4 SPOT) were deployed on white sharks around Dyer Island and in Mossel Bay. Unfortunately, we realised after deployment that one SPOT tag presented a design fault that prevented it from transmitting, and the remaining three SPOT tags were found on beaches shortly after deployment. These are very sensitive devices and sometimes the tags detach from the sharks prematurely or fall off if the shark breaches for example. One PAT tag deployed in Mossel Bay started transmitting its information after only 11 days, instead of the 12 months period set for that tag. The results from this tag were nonetheless very interesting as this shark swam about 820 km from Mossel Bay to Port St Johns in 11 days, and spent at least 24 hours continually at depths of between 100 and 750 meters.
During the second half of April 2003, Ramon Bonfil (WCS), Mike Meyer and Stephan Swanson (MCM) came to Gansbaai to deploy another ten PAT tags. The fieldwork was conducted on board Lamnidae, the White Shark Trust’s research boat, with Michael Scholl and his research assistants, Jessica da Silva, Michael Unwin and Andrew Blake. Eight tags were deployed around Dyer Island during three exceptional days during which we observed about 50 sharks. Two more tags were deployed in Struisbaai on board a MCM vessel. These tags are scheduled to release from the sharks at different set periods between 3 and 11 months. Now it is a question of patience…

In April 2003, ten more PAT tags have been deployed at Dyer Island...

In June 2003 five SPOT tags have been attached to the dorsal fins of White Sharks...

During November 2003, ten PAT tags and 16 SPOT tags will hopefully be deployed at Dyer Island and in Mossel Bay...

There is one question that probably comes to mind: Why is it so important to know where these sharks go?

A legitimate question when you consider the expensive costs involved. South Africa probably has two very good reasons for being at the forefront of white shark research. Firstly, South Africa made history in April 1991 for being the first to protect white sharks. And, secondly, South Africa is now renown as the World Capital of the Great White Sharks. But, we now know that these sharks are cosmopolitan inhabitants of the oceans, swimming far distances in relatively short periods and probably migrating between continents. How can protection measures in South Africa protect these sharks when they move out of our national waters? Unfortunately, white sharks are not protected beyond our boarders, except in a few other countries: Namibia, Australia, Maldives, USA and Malta. The ultimate solution would be to have White Sharks listed at the highest level (appendix I) on the CITES (Convention on International Trade in Endangered Species, www.CITES.org), which would protect them internationally. White sharks have been listed on the IUCN Red List since 1996 in the “Vulnerable” category, but this list is only an indicator to governments on the status of animal and plant species populations. In order to achieve these goals however, we need to learn a lot more about their population and movement patterns.

We are only starting to get to know these wonderful animals, and many surprises still await us as we get to learn more about these mysterious sharks.

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Warning

Some of the photographs shown in these pages depict hooking and handling Great White Sharks. These pictures do not reflect the White Shark Trust's foundation statement. The SPOT satellite tagging is a joint collaboration between the Wildlife Conservation Society (WCS) and Marine and Coastal Management (MCM). The White Shark Trust does not agree or support the hooking operation of White Sharks to attach SPOT tags to the dorsal fins. The White Shark Trust would like to see alternative attachment methods used without hooking and hauling the Sharks out of the water. The White Shark Trust does however support the PAT tagging program which involves normal spear tagging without direct handling.