Long Term Individual Identification of Great White Sharks (Carcharodon carcharias) using Photographic Identification for Population Dynamic Study

Michael C. Scholl is leading and conducting the White Shark Photographic Identification research programme in South Africa.

This is a well known and used technique on studies of cetacean populations (dolphins and whales). It has the great advantage of being a non-invasive identification technique, which is perfectly adapted for a study targetting a protected and elusive species such as the Great White Shark.

This research project has been running since 1997, and the results have been very positive - and the project has been a success:

• To date, over 700 sharks have been individually identified using this method, constituting the largest database worldwide on Great White Sharks.
• Over 1500 resightings have been recorded of those 700 previously identified sharks.
• Resighting of over 1500 days have been recorded, and some sharks have been resighted over 40 times at Dyer Island alone.

From April 1999 through March 2001, 1440 shark observation were made, of which 956 were documented with photographs of the dorsal fin. Of the 956 photo identified sharks, 378 represent individual sightings, and 578 represent re-sightings from the first half or from previously identified individuals, i.e. 378 sharks have been identified individually using this method during that last period only.

Period	Field time		Effort	# GWS observed		Period
[dd/mm/yyyy-dd/mm/yyy]	[days]	[hours]	[hours/day]	[number]	[sharks/hour]	[days]
06/10/1997-20/12/1997	24	113	4.71	NA	NA	76
07/08/1998-30/04/1999	106	482	4.55	156	0.32	266
01/05/1999-15/03/2001	416	1917	4.61	1414	0.74	684
16/03/2001-30/11/2001	48	224	4.67	359	1.60	259
01/12/2001-15/12/2002	155	665	4.29	841	1.26	379
Total	749	3401	4.54	2770	0.81	1664

Using this methodology, sharks can be identified without interacting with the animal directly compared to the more common tagging programmes. The identification process is also much more successful as the sharks can be identified even from a distance. To date, in over 700 field work days, 40’000 photographs have been taken, of which about 14’000 have been appropriate for identification and further integrated into the database.

The project has so far identified that:

1. Certain sharks return on a regular basis to the Dyer Island area;

2. There seems to be a distinctive spacial and temporal segregation between sexes during the summer months;

3. The average size of the sharks also seems to slowly increase;

4. Some sharks seem to move in loosely attached groupings ;

5. There is a significant transmitter and tag loss which rate can be estimated using photo identification ;

6. The average length of the sharks seems to increase slightly ;

7. This project has also given Marine and Coastal Management enough reason to extend the commercial white shark diving allowed area to include a secondary location, known as Holbaai, as the sharks seem to use the Dyer Island area differently throughout the year.

Using the stereo-photographic project (three dimensional photographs), precise measurements of the free-swimming sharks’ length, can also be estimated, possibly giving an idea on the growth of these sharks, or at least a better estimation of the shark’s size rather than just depend on visual estimation.

Several people have shown interest in collaborating in the project:

• Geremy CLIFF (Natal Shark Board) in Durban,
• Michael RUTZEN (Shark Diving Unlimited) at Dyer Island,
• Robert COPE (White Shark Ecoventures) at Dyer Island,
• Chris FALLOWS (African Shark Ecocharters) in False Bay,
• Roy and Jackie PORTWAY (Africa Sharks) in Mossel Bay,
• Mike MEYER (Marine & Coastal Management) in South Africa,
• John STEVENS and Barry BRUCE (CSIRO) in Australia.

This is obviously a great development for the project, and an international network of participants in this project will enable this regional study to become a full scale international assessment of the global Great White Shark population and their movements.

Movements between continents has been shown in a recent discovery, but chances to resight an animal between continent is slim, but yet present. The more interesting feature of this project is to investigate the movement patterns between different areas along the South African coastline.