By David Harasti - Published in Shark Diver Magazine - Issue 4 - 2004
"When
you visit an aquarium you often come across a large ferocious looking shark
with a mouthful of long pointy teeth that looks like it could devour you in
one gulp. This is the look that sends shivers down the spine of anyone who goes
swimming after watching a Jaws movie…"
Fortunately this species is quite harmless and it is the poor misunderstood grey nurse shark who's appearance gives the impression that it could indeed be one of those 'man eater' shark species. However, the grey nurse shark is no longer considered a dangerous species by divers and is a very popular shark with aquariums due to its fierce looks, big pointy teeth and ability to survive well in captivity. I liken the grey nurse to a giant puppy dog; they are a very curious species and are known to be placid when treated with respect.
The
grey nurse shark Carcharias taurus is a species found worldwide and is known
in the US as the sand tiger shark and in Africa as the spotted ragged-tooth
shark. In Australia, the grey nurse is under serious threat and the east coast
population is listed as 'critically endangered' meaning that there is a very
high possibility that the species may become locally extinct.
In the past, the grey nurse shark had an undeserved reputation in Australia as a man-eater. This reputation led to indiscriminate killing of the species by spear and line fishers from the 1950s to 1970s. The mass slaughter of thousands of grey nurse sharks led to a dramatic decline in the numbers along the east coast of Australia. Divers reacted to this decline by voicing their concerns to all that would listen and the NSW Government protected the shark in 1984, making it the first shark to be protected in the world. However, the east coast population has still not recovered since its protection in 1984 and there are serious concerns that the numbers are still declining pushing it towards extinction. Scientists have estimated that there is between 300 and 500 individuals remaining on the east coast. This is not encouraging data for the grey nurse.
One
of the major contributing factors to the species decline is its unusual reproductive
biology. Grey nurses reach sexual maturity at 4-6 years for males and 6-8 years
for females. They are an ovoviviparous species, meaning that they give birth
to pups after they have hatched from eggs within the uterus. This is where the
reproductive system gets interesting. Up to 15 embryos start developing in each
of the two uteri and the two most advanced embryos in each uterus then eat all
the other developing embryos and unfertilised eggs. This phenomenon is known
as inter-uterine cannibalism. So they have basically eaten all their brothers
and sisters before they are born!
The gestation period is also very long, lasting 9-12 months and the two pups are born at about 80cm to 100cm in length. Females only reproduce every 2nd year, therefore on average only 1 pup per female is produced per year.
Research on the grey nurse sharks in Australia has found that they migrate north - south at certain times of the year. It is believed that their migration is in relation to changing water temperatures, as they are generally found in water temps from 18 - 24 degrees celsius, and that they are also following prey species such as the jewfish and mullet.
Conservation
The
plight of the grey nurse shark is now starting to be taken seriously by the
Australian government and scientists. In June 2002, the Australian government
released a national recovery plan for the species with the main recommendation
being that all grey nurse shark aggregation areas must be protected as 'sanctuary'
zones and that all forms of fishing should be banned from these sites. Unfortunately
for the shark, fishers do not share these views and there has been strong opposition
to the protection of these sites for the grey nurse.
The largest numbers of grey nurse sharks are found along the coastline of NSW. In December 2002 the NSW Government declared 10 grey nurse aggregation sites as 'Critical Habitat' for the species. These 10 sites are where grey nurse aggregate and conduct important activities such as mating, feeding and pupping. The declaration of these 10 grey nurse shark critical habitat sites is a first for Australia and the only time critical habitat has been declared in the ocean for any species. Within these 10 sites special regulations apply for fishing and scuba diving, which minimise any potential impact from these activities on the grey nurse. Its to early to determine if the protection of these sites will benefit the shark, hopefully overtime scientists will find that shark numbers will increase within these locations.
Tracking the GNS
As
part of the grey nurse shark research program, scientists have initiated a tagging
program to gain a better understanding of their migration patterns and to provide
a better estimate of their absolute abundance in Australian waters. Sharks are
caught by divers using a baited barbless hook, which is then taken to the surface
where it is placed in a sling along the side of a boat. Tags are placed through
both dorsal fins and display a three-digit number that is easy to observe by
divers underwater. When divers observe one of the tagged sharks they can call
the 'Grey Nurse Shark Hotline' to provide details on tag number and the location.
One of the first sharks to be tagged was Neptune who was released back into the wild in May 1999 at Flat Rock after spending three years in the Seaworld aquarium located in Queensland. I resighted Neptune for the first time in June 2002 at Fish Rock in NSW, three years after his release. The distance between his release site and Fish Rock is over 400km kilometres, he looked healthy and content hanging out with 20 of his fellow buddies in the Fish Rock shark gutter.
Diving with Grey Nurse Sharks
I have been fortunate enough to dive all the grey nurse shark aggregation areas along the Australian east coast and I have several favourite locations where you can view these 'puppy dogs'. In Queensland the best spot is a site called Wolf Rock located off Rainbow Beach. At Wolf Rock it appears that there is a resident pack of females that are present all year round and the males come in over the summer months to mate.
In New South Wales, there are ten excellent locations to choose from, these are the critical habitat sites that were mentioned previously. Of these sites, my favourite spot to dive with the sharks is at Fish Rock at South West Rocks on the NSW north coast. At Fish Rock, large numbers of big males and females can be observed during winter and I have been fortunate to witness on two separate occasion's sharks attempting to mate in the shark gutter. Another good spot to view some big grey nurse sharks (larger than 3 metres) is at the Pinnacle off Forster on the NSW north coast.
An excellent location to photograph the grey nurse is at the Tollgate Islands on the NSW south coast over the January to April period. Up to 30 sharks can be found in a gutter that is only 10 metres deep and a good days' visibility excellent wide angle shots with natural light can be taken. This is my favourite spot to shoot images as bottom times are longer due to the shallow depth and the sharks are very curious at this location and will swim straight up to you. On more than one occasion I've had to move myself out of the way of a shark that was not interested in changing direction! There is even a site located on Sydney's doorstep, Magic Point located near Bondi beach and its only a 20 minute boat ride out from Sydney harbour!
So if you ever get a chance to visit Australia, try and fit into your schedule a visit to one of these grey nurse shark locations for a dive with this critically endangered species. Who knows, it might not be too much longer before diving with the grey nurse in Australia becomes a very rare event...
For further information on grey nurse
sharks in Australian waters please visit these websites:
Environment
Australia website
NSW
Fisheries website