Fin Id's as observed by White Shark Projects

FIN-ID CATALOGUE:
Over the last year consistent data has been collected on individual shark sightings. For the purposes of this document 4 individual sharks are included to show residency patterns and the periods for which some individuals remain around the Dyer Island area.
The information recorded within may not thoroughly represent the population dynamics of the species in this area. This information cannot be used to represent the population as a whole as there is a large amount of variability within the behavioural repertoire of each individual.
There are undoubtedly some individuals that will not be observed around cage diving vessels and there is no evidence to suggest that a single animal will continue to approach the boat with every successive sampling period. Some individuals may learn to avoid the vessel to due to the effects of negative conditioning and the lack of food rewards.
The 4 individuals appearing in this document have become well known over the last year and as a consequence have been named.
I have chosen these specimens to show other areas of research interests such as healing abilities, residency, growth rates and seasonal visitation.
Shark 1 – re-sights: Shark 2 – re-sights: Shark 3 – re-sights: Shark 4 – re-sights:

28/11/2008 28/04/2008 14/06/2007 15/12/2008
01/12/2008 10/10/2008 21/06/2007 18/12/2008
06/12/2008 03/06/2009 03/06/2009 21/12/2008
15/12/2008 22/06/2009 19/06/2009 26/12/2008
18/12/2008 01/07/2009 20/06/2009 29/12/2008
04/07/2009 02/07/2009 31/07/2009 11/02/2009
17/07/2009 03/07/2009 02/08/2009
18/07/2009 05/07/2009
21/07/2009 24/08/2009
30/07/2009 04/09/2009
04/09/2009
10/09/2009





Shark 1 - Kimbo:


Kimbo was originally observed at a size of 2.3 metres on the 28/11/2008. Our first observations were made in the summer grounds known as Joubert’s Dam. The right hand side of the dorsal has a ‘√’ shaped pigmentation blemish and the left hand side has a small heart shaped pigmentation blemish. Situated just anterior to the dorsal on the left hand side there was a large +/- 20 cm long, +/-3 cm deep cut. Over November and December we were able to track the healing of this cut which was astonishingly quick. Read more: Healing powers of the Great white shark. Kimbo had become very familiar with the cage diving vessel and appeared to learn and adapt her strategy over time. We are therefore recording all behaviours around the vessel to investigate cognition, memory and learning capabilities. Over the last year I believe Kimbo has grown into the offshore island population. She moved to the island from the inshore nursery ground and remained there till the end of the winter season into September 2009. It will be very interesting to see whether this particular individual moves back down into the nursery grounds for the summer. Since November 2008 this juvenile shark has increased in length by 20 cm.

Shark 2 - Nemo:
This particular individual was first identified in August 2007. Nemo is a juvenile female and was initially recorded at a total length of 2.2 metres, she has been a long term resident of the Dyer Island area.

There are a few young individuals that have remained in the area for extended periods of time (>9 months). Many of the sharks we see are highly transient remaining in the area for short periods of time (2-4 weeks), with many other animals that we do not identify satisfactorily.

This small shark had severe wounds to the dorsal fin causing it to curl over and eventually tear away leaving two thirds of the dorsal with fragmented tissue. Roughly 70% of the right hand pectoral fin is missing. It would appear that the pectoral fin was initially compressed downward. Other marks on the body suggest that she may have been caught in a net or line. The reason Nemo has shown such a large degree of residency could be a result of her injuries. Over the last year Nemo has increased in length by 30 cm and continues to surprise us that she has made it through another season, getting bigger and stronger every time she is observed. Nemo was observed on several occasions between August 2007 and October 2008, a period spanning both the summer and winter periods and locations. During our first trip to Joubert’s Dam, October 2008, Nemo made an appearance and then was not seen until June 2009. We do not know if Nemo remained in the local area or moved elsewhere along the coastline.

Shark 3 - Slash-fin:

This 3.5metre male has been a long term winter visitor to Dyer Island, arriving right in the peak season for predatory activity (June, July & August) and leaving shortly after. Slash-fin is aptly named due to the 3 large gashes that run through the dorsal fin. Initially the fin was severely damaged with the pieces moving independent of each other. Over time the dorsal fin has fused back together. Slash-fin was originally named and spotted in 2004. This male has returned to the island every winter since. Although white sharks are not considered to be territorial, Slash-fin is only usually observed at a location called South of Geyser. It is very unusual to observe him around other areas of the reef system during his brief visits unless it is when he initially arrives at Dyer Island.



Shark 4 - Gash:

Gash was originally sighted in Joubert’s Dam throughout December. When we first observed this small 2.5 metre female there was a huge gaping wound on the dorsal surface just anterior to the dorsal fin. It appears this wound was most likely caused by a boat propeller. Gash and Kimbo have given us the opportunity to try and establish how fast white sharks are capable of healing after severe trauma. We did not encounter Gash in January and only caught a brief glimpse of her on one trip on the 11/02/2009. This allowed us to gauge how well her wounds had healed throughout this period. The results were astonishing with her showing a very rapid rate of tissue recovery and mobility. It is unclear whether this particular individual had remained in the area throughout January or left the area and returned. There were reports of her by other vessels. This is a clear limitation of the dorsal fin identification catalogue as a method to continually track the localised movement patterns of sharks in the area.


Conclusion:
The population composition of this area is very complex. There appears to be two distinct seasonal grounds, the South African summer and winter compositions. The composition during summer typically consists of large (4.0 metre) females and juveniles (1.2-2.5 metres), males and intermediate (2.5-4.0 metres) size classes are usually absent or rare. During the winter season the shark’s frequent Dyer and Geyser islands for the purposes of hunting the seasonal abundance of Cape fur seals. Males and females are observed in equal proportions and intermediate size classes (2.5-4.0 metres) are usually common.
Sharks that are approaching adulthood may navigate South Africa’s coastline and stop at these off shore islands for short periods of time to take advantage of the abundance of food. They do not appear to stay for long periods of time, usually <1 month. It could be that once they have exhausted the food resources in a particular area they move elsewhere to hunt. Whilst they are hunting I believe that some individuals such as Slash-fin are semi-territorial, having preferred hunting locations and drop off points along known seal run-ways. The younger animals appear to float between hunting sites and don’t appear to hold territories for any sort of consistent time period.
Nemo and Kimbo were summer sharks, observed down in the shallows in the nursery ground area. Both sharks would later be present at the island in the winter suggesting potential recruitment into a more transient population with a highly migratory mode of lifestyle. We will have to wait and see if any of these animals show up in the summer grounds this season.



To follow these sharks, visit our website: www.whitesharkprojects.co.za

Some interesting facts on great white sharks

The shark of fiction and the shark of fact is not the same shark.....

Great white ID
Quite simply, great whites are grey on top with a white underbelly – for perfect camouflage from above and below. The white belly blends in with the sky and the dark back blends in with the rocks below.

Great white addresses
Great whites swim the oceans of the world. Concentrations, or 'hot spots', are found in the temperate waters of south-western Australia, South Africa, California and Mexico. The densest known population is right here, around Dyer Island, South Africa!
They are pelagic fish. That means they prefer the upper layers of the sea, but also venture down to 1 280m. They are mostly seen in coastal waters where the pickings are rich. Seals, whales, dolphins, other sharks and large bony fish make a good shark diet.
We've recently realised that great whites spend a lot of time in the open ocean too. When 'Nicole', a female great white, was tracked to Australia and back, we learned so much more about their migration and behaviour. In fact, great whites have the longest recorded migratory range of any marine creature. Nicole covered a staggering 22 000km from Dyer Island (South Africa) to western Australian and back in just under nine months! Her average swimming speed was 4.7km/hr. She spent 60% of her time in the top 5m of water, 20% in the area below that and 20% down at her maximum depth of 980m.

Favourite foods
The white shark is an apex predator – right at the top of the feeding pyramid – and is vital to a healthy marine ecology. The only animals who attack them are other great whites, sperm whales and orcas.
These apex predators take their pick of the buffet, choosing fish, smaller sharks, turtles, dolphins, seals and sea lions – or even the blubber of dead whales.
Great whites are partly warm-blooded. Most of their body is kept at 14°C above the temperature of the surrounding water. They are economical with their calories and can go for weeks between meals. With one bite, great whites gobble about 14kg of flesh, and can gorge on several hundred kilograms of food. Do they like the taste of humans? Well, humans are not exactly healthy for a great white because its digestion is too slow to cope with the human body’s high ratio of bone to muscle and fat...

Vital statistics
Great whites of up to 7m (21ft) long have been reliably reported, but their average length is around 6m (18ft). They're over a metre long at birth (3 to 5ft).
No one really knows how long great whites live. It's hard to find out because they lead lonely lives and are so migratory. Research in recent years should bring us closer to knowing.

Power-sensing!
Great whites have powerful sensing mechanisms – a mega sense of 'smell' and an ability to sense the electrical fields radiating from living creatures.
They 'breathe' via gills, so nostrils are solely for sniffing out prey. Each nostril is divided in two, separating the water into two flows, one incoming and one outgoing. The water flows over sensory organs covered with millions of olfactory cells connected to the 'smelling' centre of the brain. The great white is one big swimming nose!
They hunt down prey with an unusual electrical field detection system. Minute capsules filled with a gel-like substance are sensitive to electrical discharges as small as .005 microvolts! Sensory cells pick up these signals and transmit the information to the brain. All marine creatures generate small electrical fields – where their skin meets the water, from the mucous membranes in the mouth and gills of fish, or from the blood of wounded animals. The great white 'reads' the signals and decides who's swimming normally, who's panicking, or who is incapacitated.

A sharky grin
When a great white attacks, it thrusts its jaw forward. This makes for the widest possible grab and lets teeth grasp the prey.
Sharks' teeth change over time depending on what they eat. Smaller sharks, less than 3m, generally eat fish. These young sharks have pointed teeth so that their jaws can pin prey. As they get bigger, they start to add larger prey such as seals and dolphins. To dismember such big animals, their top teeth become stronger, serrated and triangulated. The lower teeth stay pointed so that the shark can still pin the prey.

What's with the eyes?
Much like human eyes, shark eyes have a light-sensitive layer at the back called the retina. A shark's retina has millions of microscopic rod cells helping the shark see in dim light.
In low light, shark eyes shine like a cat's. That's because the tapetum, a layer of shiny cells behind the retina, reflects light back through the eye helping them see even better in low light. In bright light the tapetum can be covered with dark cells to cut reflection and protect the retina.
Sharks have two eyelids to protect their eyes. Often the eyelids don't meet. Some sharks have a third eyelid (nictitating membrane) – useful protection when attacking prey. If there's no nictitating membrane they roll the eyeballs back under the true eyelids – and there's the white-eyed look.

Mystery and reproduction
Male great whites are ready to breed when they reach approx 3.8m long. Females are ready at approx 4.8m. Though they both have a hole near the pelvic fins called the cloaca, you can see the difference between male and female sharks.
Male sharks have modified pelvic fins called claspers. They also have two muscular sacs in their abdominal wall which they fill with seawater. Internally males have testes that produce sperm and secrete male hormones.
Female sharks are mostly bigger than male sharks. Other than that, they look the same, except they don't have claspers. Inside, they have a pair of ovaries where female hormones and eggs are made – interestingly, usually only the right ovary makes eggs.
We know almost nothing about how and where great whites mate. Some believe that making a large kill has a soporific effect on them that may lead to mating.
We have never seen a great white give birth, though we know they are ovoviviparous. That means the eggs grow inside the female, hatch there and carry on growing until they are born between spring and summer. They give birth to between 4 and 14 pups and may have only 4 to 6 litters in a lifetime. At birth, the pups are about 1.5m long and are already able hunters. They grow quickly, reaching 2m after their first year of life.

White shark titbits
White sharks store extra fat in two large livers and draw on these stores when times are hard. The livers help to keep the shark buoyant.
The dorsal fin is flexible (bendy) and works with the tail to make the shark agile.
The dorsal fin is as individual as a fingerprint – the trailing edge and the arrangement of notches in the fin is unique.
The great white is the only apex predator that hasn't been kept successfully in captivity. Where it's been tried, the sharks were released due to stress.

Conservation: It's tough at the top
Being at the top of the food pyramid means white sharks are vital to a balanced marine ecology. They control the populations of prey species and weed out the sick and wounded. A healthy ocean depends on a robust population of apex predators. Sadly, the survival of the great white is threatened by the ignorance and greed of humankind who continue needlessly to slaughter them. Responsible tourism promotes conservation, awareness and respect for the great white shark. We work towards sustainable populations of great whites in the waters of the world.

To join in our shark tourism trips, visit www.whitesharkprojects.co.za