January 2004 Shark Bytes
Posted on Saturday, 31 January 2004
We have had an extremely quiet shark month this January and have not been able to go to sea once due to high winds. It is definitely the worst summer we have experienced, so we took the opportunity to escape the wind and spent 3 weeks in The Kruger National Park looking at and photographing land-based animals. Well, we escaped the wind only to be flooded and one evening the water was ankle deep in our tent!
We actually had one very special encounter with a Tusker Elephant. Tuskers are very rare and there is said to be only 7 alive in the Park. A Tusker is a bull elephant with extremely long and heavy tusks. We came across this Bull early one morning and spent 6 hours watching him. In the end he was no less than 5 meters from our car. He was very tolerant with us, as most elephants don’t appreciate cars this close! His right tusk was touching the ground and the left formed a beautiful curve upwards 10 cm from the ground. Chris & I were so over-come with emotion being able to be close to this animal which has to be one of THE great individual animals alive in Africa at the present time. We later found out that his name is “Mabarula”, ironically meaning “Big Foot”.
Although we did not get out to sea this month we still managed to see sharks, and quite a few too. From October to early March each year we have a very big interest in going to watch the “treknets”. The English word for this is beach seine net fishing. The word “trek” means “pull”, describing how this type of fishing is conducted. Shoals of fish are usually spotted from shore and a rowing boat is then rowed out to this area. They can row up to 600 meters out, but usually the range is about 100m to 200m. A semi-circular net is deployed and then retrieved by being pulled in by 2 groups of trek fishermen on either side of the net. The net forms a bag that collects anything that is in the area that is being pulled over. Fish species being targeted are Yellowtail, Mullet, kob and elf/blue fish. There is of course a large amount of bycatch and this is where our interests lie as sharks and rays make up most of this.
There are certain conditions that are better for sharks. When strong onshore winds blow, the water is churned up providing ideal conditions for a microscopic plant called Anaulus australis to grow. The water takes on a brown colour when the water is nutrient rich. The Mullet come into this shallower water to feed on the Anaulus australis and larger fish feed on the mullet. The sharks will be feeding on both the mullet and kob, blue fish etc.
Chris first started tagging and releasing sharks caught in the False Bay treknets in 1991. Up until this point most sharks were harvested and sometimes just left to rot on the beach. As a teenager Chris managed to persuade the crews to let him tag some of the sharks and now almost all sharks are released.
In the roughly 500 treknets that Chris has gone too he has tagged about 180 bronze whaler or copper sharks. These are the sharks that are most commonly caught. They are extremely powerful animals and can be difficult to hold down while tagging them as they trash around tremendously. Fortunately they are very tough animals and nearly 100% survive the capture. From the tagging we have learnt some interesting facts. One shark moved from False Bay all the way up the East coast and was caught again in Mossel Bay 526 km away. The largest shark tagged was 2.95 meters total length. We cannot find records of a larger recorded bronze whaler. The smallest one tagged was just 80 centimeters! Also on one occasion 30 to 40 bronze whalers were caught in the same trek!
Chris has also tagged 11 Common Threshers. This is a most beautiful shark with an elongated tail. The tail is actually about half the total length of the shark’s body and the Afrikaans (South African) name for it is “Sjambokhaai” meaning “whip shark”. The thresher predates on its prey by stunning it with its tail. It also tries to do the same thing when one is trying to tag it on the beach, so you have to watch out!
The Ragged Tooth shark or Sand Tiger or Grey Nurse shark is a protected species in South Africa so these have to be released. By tagging them valuable information has also been learnt. Of the 11 tagged by us one shark was first tagged when it was caught in the Natal Sharks Board (NSB) nets in Durban. It was the tagged by Chris in False Bay, 1800 km away and was then once more caught in the NSB nets. I am not sure if this shark was extremely lucky or unlucky! These sharks have also varied in size from 108cm to 278.5 meters total length. They are very docile and can sometimes appear that they have died in the net.
The practice of tag and release plays a very important role in conservation. Not only is the species caught been given a second chance, valuable information can also be learnt from re-captures. For instance: growth rates, population sizes and migratory movements can be determined. This is especially important to know as the information can be used not only to protect a species but an area as well.
Other species that have been tagged and released include smooth hammerheads, black spotted smooth hounds, soup fin sharks and one cow shark.