I first met Meag in 2009 when she came to CPUT to do a presentation on Elasmobranchs for our class. Meag’s presentation included Elasmobranchs’ biological and physical characteristics as well as the unsustainable exploitation sharks face due to South Africa’s fishing industries.
(FYI : South Africa has a dedicated Shark longline fishery as well as a bycatch allocation in the hake longline and trawl fishing sectors.)
Meag’s passion is obviously contagious, and what started out as mere curiosity on my part soon blossomed into an intense desire to learn as much as possible about these beautiful and hugely misunderstood animals, which form a vital part of the marine ecosystem.
Meag and I stayed in touch. I was over the moon when she invited me to spend my 3rd year internship and The South African Shark Conservancy (SASC) with her in Hermanus.
So....here I am!! Having the most amazing experience of my life – catching, tagging and releasing the “ferocious” Bull/Zambezi Shark Carcharhinus leucas in the Breede River Estuary in South Africa! Meag and another team of researchers were here in 2008 and were able to tag and track a 3.4m female which made newspaper headlines in January 2009.
We arrived at the Breede River in the Overberg region on Thursday the 21st of January 2010, and quickly settled into our accommodation in the Witsands area of the river.
It is quite a process to catch a shark. It starts at the bottom of the food chain, with the pumping of mud prawns to use as bait to catch fish (preferably Grunter - pomadasys commersonni) which is used as live bait to lure the shark onto the line. Circle hooks are used to ensure that the hooks can easily be removed with the least amount of damage inflicted on the animal.
It didn’t take long to hook the first shark, a 2.9 meter male.
From the first tracking expedition in 2009 and the catch of the large female (named Nyami-Nyami) it was hypothesised that the river was used as a nursery ground for the Zambezi. The capture of the large male has blown that theory out of the water! Male Zambezi sharks are thought to be territorial and it is assumed they will not tolerate smaller younger sharks in the area.
So now????
We measured his straight and curved length, precaudal and fork length as well as attaching a continuous acoustic tag which allows us to track him via a receiver called the VR100 and a directional hydrophone. A fin clip is taken for DNA comparison, any parasites that the animal may have are collected, and Oxytetracycline is injected into the shark in the hope of determining the age of the shark if he is ever recaptured. The ‘oxytet’ stains the animal’s cartilage which grows in a similar fashion to the rings of a tree trunk, and assists in determining the age of the shark.
We started tracking “Jeremy” the next day, and found him roughly in the same area we released him. That same day got a call informing us that the 2nd shark, also a male about the same size, had been hooked right in front of the Lodge near the mouth of the river. We decided to call him Pumpkin! The same procedures mentioned above were applied to “Pumpkin”.
Up until now, we have been tracking both sharks in three hour periods for each shark. From today both sharks will be tracked for 12 hours a day, unfortunately the lack of manpower has prevented us from tracking at night. While tracking, we record the shark’s location, depth and water temperature every 15 minutes. Every half hour we record the water pH, conductivity, NTU (nephelometric turbidity units), and dissolved oxygen from the river floor, every meter to the surface.
So far we have tracked Pumpkin up as far as Bobbejaankrans on the river approximately 20 kilometres up the river – quite far from the site that he was hooked. Jeremy seems to enjoy travelling from boat to boat, waiting to steal fish that the locals have hooked! A smart opportunistic predator!
From the data we are collecting, we are hoping to answer some pressing questions:
1. Why do Zambezi sharks occur in the Breede River?
2. What is the population size of these sharks in the river?
3. Is this population genetically separate from other Zambezi populations around South Africa?
Will keep you all posted!!!!
Cheers Tamzyn
(FYI : South Africa has a dedicated Shark longline fishery as well as a bycatch allocation in the hake longline and trawl fishing sectors.)
Meag’s passion is obviously contagious, and what started out as mere curiosity on my part soon blossomed into an intense desire to learn as much as possible about these beautiful and hugely misunderstood animals, which form a vital part of the marine ecosystem.
Meag and I stayed in touch. I was over the moon when she invited me to spend my 3rd year internship and The South African Shark Conservancy (SASC) with her in Hermanus.
So....here I am!! Having the most amazing experience of my life – catching, tagging and releasing the “ferocious” Bull/Zambezi Shark Carcharhinus leucas in the Breede River Estuary in South Africa! Meag and another team of researchers were here in 2008 and were able to tag and track a 3.4m female which made newspaper headlines in January 2009.
We arrived at the Breede River in the Overberg region on Thursday the 21st of January 2010, and quickly settled into our accommodation in the Witsands area of the river.
It is quite a process to catch a shark. It starts at the bottom of the food chain, with the pumping of mud prawns to use as bait to catch fish (preferably Grunter - pomadasys commersonni) which is used as live bait to lure the shark onto the line. Circle hooks are used to ensure that the hooks can easily be removed with the least amount of damage inflicted on the animal.
It didn’t take long to hook the first shark, a 2.9 meter male.
From the first tracking expedition in 2009 and the catch of the large female (named Nyami-Nyami) it was hypothesised that the river was used as a nursery ground for the Zambezi. The capture of the large male has blown that theory out of the water! Male Zambezi sharks are thought to be territorial and it is assumed they will not tolerate smaller younger sharks in the area.
So now????
We measured his straight and curved length, precaudal and fork length as well as attaching a continuous acoustic tag which allows us to track him via a receiver called the VR100 and a directional hydrophone. A fin clip is taken for DNA comparison, any parasites that the animal may have are collected, and Oxytetracycline is injected into the shark in the hope of determining the age of the shark if he is ever recaptured. The ‘oxytet’ stains the animal’s cartilage which grows in a similar fashion to the rings of a tree trunk, and assists in determining the age of the shark.
We started tracking “Jeremy” the next day, and found him roughly in the same area we released him. That same day got a call informing us that the 2nd shark, also a male about the same size, had been hooked right in front of the Lodge near the mouth of the river. We decided to call him Pumpkin! The same procedures mentioned above were applied to “Pumpkin”.
Up until now, we have been tracking both sharks in three hour periods for each shark. From today both sharks will be tracked for 12 hours a day, unfortunately the lack of manpower has prevented us from tracking at night. While tracking, we record the shark’s location, depth and water temperature every 15 minutes. Every half hour we record the water pH, conductivity, NTU (nephelometric turbidity units), and dissolved oxygen from the river floor, every meter to the surface.
So far we have tracked Pumpkin up as far as Bobbejaankrans on the river approximately 20 kilometres up the river – quite far from the site that he was hooked. Jeremy seems to enjoy travelling from boat to boat, waiting to steal fish that the locals have hooked! A smart opportunistic predator!
From the data we are collecting, we are hoping to answer some pressing questions:
1. Why do Zambezi sharks occur in the Breede River?
2. What is the population size of these sharks in the river?
3. Is this population genetically separate from other Zambezi populations around South Africa?
Will keep you all posted!!!!
Cheers Tamzyn
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