Foul weather plays havoc with expedition

It's now day four of our National Geographic expedition to the Breede River, and here we sit bundled against the cold, blustery weather more reminiscent of the Cape winter than a mid-summer day. We are counting down the days until the end of our trip here... three more to go and still no sharks. But this is how field work plays out - we are completely dependent on Mother Nature and can't launch our boat in gale force winds, which the weather service tells us will continue for the next two days. This leaves us one day to capture and tag the Zambi we're looking for.

Attitudes are positive, however, and the fishing crew have moved upriver in the hopes of catching live bait from the side. Once we have some good fish and clear weather there will be an excellent chance of catching a Zambi - we just hope the weather service is correct in their predictions and that we will have at least one clear day to hit the water and fish hard.

In the meantime, the weather gives the scientific crew a good window to continue entering and analyzing our data from the last trip. Perhaps not as exciting as fishing, but definitely a crucial part of our study here.

If we are unable to fish for sharks in the coming days, Nat Geo hopes we can return in the near future to continue filming for their series.

We'll keep you updated...

Cheers,
the SASC crew

February Zambezi shark expedition with National Geographic

On February 19th SASC will once again be returning to the Breede River to conduct further research into the population dynamics and behaviour of Zambezi sharks in this unique system.

This time around we will attempt to capture another shark and surgically implant an acoustic tag with a battery life of 5 years, which will enable us to follow the animal's movement in the river for a long-term period using an array of underwater receivers. If the shark departs the river and passes by Mossel Bay or any other estuary/coastal area where acoustic receivers are deployed, we will be able to track its movement using a unique code transmitted by the implanted acoustic tag.

It is hoped this will help us determine where the Breede River Zambezi sharks go in winter, and what other river systems they may frequent. Pending sufficient funding we hope to deploy several more of these tags in the coming months/years.

The upcoming expedition will be filmed by National Geographic & SASC is grateful to them for funding this leg of research.

Special thanks also go to Marc Rubelli and Faiz Khan (Rock Hustlers Fishing Tackle) for their support during the previous expedition, and continued support this time around.

Stywe lyne,
Meag

My experience catching & tracking Zambezi (bull) sharks in the Breede River, South Africa

26th January 2010

I’m Robert, a second year MSc student in Zoology at the University of Cape Town, and a member of the 2010 Breede River Zambezi Expedition.

In the first week, we have managed to deal with a lack of fresh bait, high winds and rough water and have successfully tagged and tracked two large male Zambezi sharks. Two more were hooked, but managed to roll, break the line and escape. They will be the ones that got away but we are keen to catch a third shark this week as we still have a passive transmitter tag to deploy. We all agree that the Breede River system is extremely productive, and speculate that the system might even support around 20 sharks distributed throughout the reach of the river. A large number of top predators in a system is an indicator of good health and sustainable exploitation, and it seems that the Breede River is no exception!! However, careful management in the future will need to be implemented if we want this condition to continue.


The tags we have equipped the sharks with emit a supersonic pulse that is picked up by a hydrophone held underwater and a receiver unit. It can pick up the signal from approximately 500 meters away, depending on water conditions and is directional, so we know exactly where the shark is. In bad weather and rough water it is more difficult to discern a tag transmission from all the background noise in the water: waves crashing against rocks, waves breaking, even the sound of the current running against mud or seagrass!

Every 15 minutes we log a datapoint where the position of the shark we are following is and every half an hour we take a depth profile of salinity, water temperature, turbidity and conductivity. This will allow us to determine if the sharks prefer to use certain waters, or if they follow the current and salinity wedge upriver from the estuary. However, this will only become apparent when the data is spatially mapped. We measure these by using an YSI unit, which is an array of sensors held underwater. We raise it 1 meter per reading, so that we see the different measurements at different depths.

As of yet, we are not sure why the sharks are here. We can speculate though, and have come up with a few theories. Originally we thought that the sharks we coming here to pup. However, the sharks we have caught on this expedition have been huge males, making it unlikely that females come here to give birth. However, last years expedition tagged a large female, thought to be pregnant. We cannot say for sure if there are no females at all in the river. We still have to fish further upstream, where there is the possibility of small sharks, juveniles or (fingers crossed!!) neonates, which may be out of the predation zone of the larger adults. On the other hand, this is a very productive system, so the sharks might be using the system as a feeding ground on their way or before a migration to breeding grounds. Last night was the spring high tide, and this morning the tracking team found the sharks further up than their usual haunts. Either way, only further research will prove any theories we can put forward now.

Paul Van Nimwegen - SASC intern - speaks about his experience catching & tracking Zambezi sharks on the Breede River

My name is Paul Van Nimwegen. I am a third year Fisheries Resource Management student at CPUT. I met Meaghen McCord from the South African Shark Conservancy (SASC) at a presentation on sharks (elasmobranchs), explaining the importance and vulnerability of these majestic creatures. SASC is a non-profit organisation, aimed at public education, research and promoting the sustainable use of sharks.

As a keen angler and biologist, I jumped at the opportunity to join the SASC research team on their January 2010 Zambezi shark expedition to the Breede River. I called Meag to find out more about the expedition & a week later I was standing on the banks of the Breede River.
Our first day was spent collecting prawns and catching grunter, which was used as live bait for catching the Zambi’s. I was slightly sceptical at first and wondered how long it would take to hook our first shark. Will 15 days be enough? Will we catch one?

Within two hours we had hooked up and 3.5 hours later, we landed a 2.9m male Zambezi. The shark was tagged, measured and biological samples were taken. Acoustic tags are used as this indicates their position and movements in the estuary. The tags also detect water temperature and depth at the sharks’ exact location. Two days later we landed another male Zambezi of 2.97m. This shark was also tagged and measured and relevant biological samples were taken.

Tracking of the sharks then commenced. The sharks are being tracked 12 hours per day, and information on location, temperature and depth is recorded. This can be tiresome and frustrating at time, but very rewarding nonetheless. We are hoping to capture one last shark before the end of the expedition, and deploy our third and final tag. Although we have managed to hook two other sharks in the last few weeks, we were unable to land them. The good news is there are at least a few other Zambezi’s in the system!

Yesterday (Monday, February 1st), we witnessed a Zambezi actually taking a large kob on the surface of the water near the Breede River Lodge. The kob was lacerated and bitten off towards the tail. The remaining carcass of the kob weighed 19kg and was therefore estimated to have a whole weight of 25kg! This was an amazing event to witness!

We have truly had the most amazing journey thus far, exceeding all of our expectations. Through our research here we hope to explain the occurrence of these sharks in this estuary and monitor their behaviour and movements over the long term.
As for the time being, it is important for us to protect these mighty creatures that call the Breede River home.
Stywe lyne, Paul

News from the Breede River: SASC interns report back

Hi there, I am Tamzyn, a 3rd year Fisheries Resource Management student at The Cape Peninsula University of Technology (CPUT).

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