Diving and Laje de Santos

They say good things come to those who are patient. I never really gave this saying too much thought until just recently…In the name of manta research I have spent six solid weeks (during the winter of 2009 and winter of 2010) diving a remote offshore rock called Laje de Santos in the south of Brazil looking for the elusive giant manta (Manta birostris). Until today, I have searched in vain. I was the one that actually chose this location for part of the worldwide study on this newly discovered species of ray, as this little spec of a rock is the largest documented aggregation site for this species in the southern Atlantic Ocean. But, to tell you the truth, despite my normal determined outlook when working in the field, I was really beginning to loose hope (and that’s pretty bad, since my current international research campaign is ironically named “Ray of Hope’).

Andrea in the field at Laje

But that’s the funny thing about marine field research and, I suppose, diving in general. It doesn’t matter what the ocean throws at you…countless hours of searching, dozens of dives in cold, green water, boat trip after boat trip on rough, windy seas…all of the excruciating effort and disappointment literally seems melt away the second the animal that you have been searching for appears. Your breath catches in your throat, time stands still and everything seems to make sense in the world. And this is why we divers torture ourselves by squeezing into unbearably uncomfortable wetsuits, why we swim around the sea covered in all kinds of tanks and hoses, and why we spend all of our money and time bobbing around in the middle of the ocean. It is precisely for this sensation and these encounters with special marine creatures. For the majority of us, the most precious encounters are with large, elusive megafauna like sharks, whales and dolphins. The object of my affection, of course, is the manta ray.

Andrea patrolling with sat tag

So, as I was saying… all hope seemed lost when about five days into my latest expedition to Brazil a huge storm hit. It poured rain for a week, the wind howled across the sea and the swell was unrelenting, turning the clear, blue, offshore water into the kind of green that divers have nightmares about. When we finally were able to return to the sea, the visibility was only a few meters and the water was bitterly cold. Our only recourse was to patrol up and down the tiny offshore rock… searching for a miracle.

And then one appeared, literally out of the gloom, and it was coming straight for us. It felt like a dream. He was massive, a large mature male manta, and he was ready to be the ambassador for manta ray conservation in Brazil.

Out of the gloom...

Almost as if he understood what was needed of him, he swam right up to us (hovering momentarily to get his belly tickled by our bubbles) and patiently allowed me to take an ID photo him and place a single satellite tag on his dorsal surface. Watch Andrea sat tagging the first giant manta ray in Brazil! Without even the slightest flinch, he continued to swim with us after the tag was inserted, allowing me to check that the tag was secure and more importantly allowing me to get to know him a little better. For several minutes I took detailed images of every important feature from every conceivable angle. I was amazed by the gentle tolerance of this individual; the experience reminded me how incredibly privileged I am to work on them and how much they deserve our respect and protection.

Then without warning he slowly began to move back off into the gloom, ready to lead us on one of the most exciting journeys of my career. The tag that I placed on was archival, meaning that it functions like a mini laboratory, constantly sampling the outside environment and storing the data for me as the manta ray swims around the ocean.

And he is off...

Amazingly, it records the temperate of the surrounding water, the depth the manta is in as it moves along or makes deep dives, light levels (which are used to determine the actual track of the manta) and GPS positioning should he come to the surface periodically. I manually programmed the tag to automatically detach after 180 days (6 months) at which point it will float to the surface and begin to download all of the stored data to the ARGOS satellites. At this stage, ARGOS will magically beam this information to my computer. Just thinking about this process makes me love being a scientist in the 21st century. To have the technology to be able to ask and then answer difficult questions is such a joy.

At this stage, all we have to do is sit back and wait. For the next six months this individual will roam the cold waters of the Atlantic Ocean storing the secrets of his lifestyle and behaviour; secrets that have eluded us until now.

Over the next few months, we will begin to see things from his perspective...

But already this particular manta ray is a part of history. He is the first manta ray to be satellite tagged in South America or in the southern Atlantic Ocean for that matter and the information that he will contribute with be both unique and invaluable.

This particular individual happened to be a re-sighted male, which had been previously encountered at Laje back in 2007. He had not been seen since his first encounter, but this is not entirely unusual for the area. It is thought that manta rays only make brief stopovers to this offshore oasis before moving off into the unknown. The ‘Mantas do Brasil’ project  (Laje Viva Institute), managed by Guilherme Kodja, is specifically trying to address this mystery and have teamed up with my Foundation (Marine Megafauna Foundation) to answer some key questions.

Success! 1st satellite tagged manta ray in South America!

Where do these giants come from? Where do they go when they leave this little rock? Why do they mysteriously appear each winter and what are they coming to do? How are humans impacting their movements and their natural behaviour? Are they affected by the massive amount of shipping traffic that occurs in the region? How many are caught each year in gillnet fisheries along the coastline? With next to nothing known about their lives in this part of the world, these answers could prove invaluable to our ability to manage the manta ray population in the region and protect them from anthropogenic threats.

Collaborative research at its best!

As we continue to learn more about these ocean giants, I also continue to learn and grow as a scientist. Patience is an important skill in field research as is the determination to see difficult projects through to completion. In the end, persistence will pay off, and although we sometimes feel that we are racing against time, we are ultimately at the mercy of the animals that we study and the elements of nature. Sometimes sitting back and waiting for them to come to us is the only solution.

Our keynote speaker, Dr. Christopher Lowe, described how major advances in our knowledge of shark behaviour have been achieved over the last 25 years thanks to the evolution of some key technologies. The original interest to better understand shark behaviour was driven by the military’s interest in protecting personnel and equipment from sharks. Early behaviour research focused on sharks’ sensory systems and basic biology, subjects about which very little was known.

Sharks International Delegates. (Photo: Cheryl-Samantha Owen / SOSF)

Sharks are global travellers and observing them in the wild is no easy task. The biggest change to shark behaviour research arrived with the advent of acoustic and satellite telemetry. These technologies, which use tags to record a wide array of sensory data, enable scientists to track the exact locations of where individual sharks travel and the temperature, depth, and light levels that they experience on their journeys. Through telemetry we have expanded our knowledge of movement patterns, feeding and mating behaviour, as well as an understanding of the physiology that drives these behaviours. There has been a growing trend in the number of scientists using telemetry technology and in fact, over 20 per cent of the talks at this conference include the use of telemetry. On your next dive if you are lucky enough to come across a shark decorated with a research tag it could belong to one of the scientists attending the conference here. Blacktip reef sharks, whitetip reef sharks, whiptail stingrays in the Amazon estuary, shovelnose guitarfish, manta rays, bull sharks, blue sharks, whale sharks and white sharks are the main characters of some of the tags here that are well on their way to unraveling some of their species’ mysteries.

Dr. Lowe did however warn us about his “shiny new hammer” theory. (You can drive in a screw with a hammer, but it may not always be the best tool.) “Scientists must focus on hypothesis driven questions or, at up to 2,000 USD a tag, they may find themselves on very expensive data fishing expeditions,” said Dr. Lowe.

SOSF scientist Dr. Andrea Marshall (also known as the Manta Queen, from the 2009 BBC documentary) presented her work on seven years of observations of the size, population structure and migratory behaviour of the newly described giant manta ray (Manta birostris). From her base in southern Mozambique Dr. Marshall has identified over 130 individuals at an inshore aggregation site, which supports both feeding areas and cleaning stations. Preliminary data from two satellite tagged individuals have demonstrated that the species is capable of international migration – a crucial consideration for future regional management plans. As well as discovering the species Dr. Marshall has also discovered that this manta is one of the  deepest (reported) diving fish in the sea.

Dr. Andrea Marshall presenting her findings at the Sharks International Conference (Photo: Cheryl-Samantha Owen / SOSF)

Dr. Jeurg Brunnschweiler later revealed his results on the small-scale movement patterns of bull sharks in the Shark Reef Marine Reserve off the southern coast of Viti Levu, Fiji. More than 60 bull sharks fitted with acoustic tags collected this data, while 14 pop-up satellite archival tags were deployed between 2004 and 2009 to monitor the movement of bull sharks away from Shark Reef and their passage through the water column.

In the beginning shark behaviour research resulted from the need to answer, “How can we protect humans from sharks?” The tide has since turned and, with as many as 73 million sharks killed each year, today we are all asking, “How can we protect sharks from humans?” Collecting and analyzing all this data is a giant step towards providing some answers to this question.

The day ended with the Oceania Chondrichthyan Society (OCS) dinner.  Not only was it an evening of mingling with some of the brightest and most passionate minds in shark science, but we were also treated to the presentation of a new shark species Pseudogaleocerdo idioti (a rather cuddly, fluffy, and soft-toothed type of tiger shark).

Pseudogaleocerdo idioti

A Caribbean reef shark in a mild form of tonic immobility whilst being blood sampled by the CEI shark team.

One of the biggest problems facing anyone interested in the physiology fish is how to generate a baseline level of blood chemistry.  What does the blood chemistry of a fish look like if it hasn’t been captured, handled, poked and prodded all in the name of science?  What are the normal levels of lactate, glucose, carbon dioxide etc., to which we can compare our “stressed” samples to?

For small fish this is relatively easy.  Take the recent work on bonefish by the Flats Ecology and Conservation Program here at Cape Eleuthera Institute.  Bonefish were housed in darkened holding chambers with a steady supply of fresh seawater for 36 hours upon which they were rapidly removed and blood sampled before the blood chemistry could change.  However, it is a tricky proposition to try and apply this technique to a 6ft Caribbean reef shark!

To try and generate a baseline level of blood chemistry for stress physiology work described in the previous post, the shark research team travelled from Eleuthera to Stuart Cove, a well known dive operator in Nassau.  Stuart Cove have been conducting regular shark dives for the last thirty years and the Caribbean reef sharks they deal with are very used to human presence in the water.  The more experienced handlers can gently halt the motion of the shark through the water by gently rubbing a chain mail shrouded hand on the nose of the shark where ultra sensitive electro-reception pores are situated.  This action appears to initiate a response similar to tonic immobility, a reversible coma-like stasis, which is usually triggered by inverting the shark.  The response initiated by the handlers is not as strong as true tonic immobility, but it was hoped that it was strong enough for a diver to quickly draw some blood, thus gathering a sample from a shark that had not been captured or interfered with in any way – a baseline.

For the most part it worked – taking blood in full SCUBA gear, laying on you back under the tail of a shark with your hands clad in chain mail was a tricky thing to do.  And although the sharks were in a mild form of tonic immobility they did not appreciate a clumsy human prodding them with needles, so unless the needle was put in the right place at the first try, they tended to swim off.  Two and a half days of diving provided us with numerous dulled and bent needles, frustrations and thankfully three blood samples.  The blood chemistry values derived from the three samples were vastly different to even the shortest longline hooking durations and represent the first true baseline blood samples taken from a large free swimming shark.

Special thanks must got to Stuart Cove himself whose generosity with his staff and boats were unparalleled.

A Caribbean reef shark blood sampled underwater.

Stuart Cove Shark Dive

Drawing Blood from a mature male Caribbean reef shark.

Small scale longline surveys are the predominant method for investigating shark populations, and when longlines are implemented on a much larger scale, are responsible for the widespread commercial harvest of sharks all over the world. Any capture event, including longline capture, unleashes series of physiological and physical disturbances, the issue is that very little is know about how this physiological stress impacts the behaviour of an animal post release, or if indeed the animal survives.

This year’s project took a two stage approach to begin to investigate the effects of longline capture on the Caribbean reef shark (Carcharhinus perezi).  Firstly, blood samples were taken from sharks that were captured during our longline surveys, using hook timers to accurately determine the amount of time the shark had been on the line.  Blood was taken from the shark and portable blood analysers were used to quantify various blood chemistry parameters which in turn indicate the level of physiological stress the shark was under for a given duration of hooking.  Secondly, a subset of fifteen sharks were equipped with acoustic transmitters which emit an ultrasonic series of pings every 45 seconds which can be detected by an array of underwater hydrophones.  These transmitters had a three-dimensional accelerometer incorporated into the tag which measured the activity level of the shark every 20 seconds post release, the data for which was in turn transmitted and stored on the seabed hydrophones.  The hydrophone array itself consisted of 32 receivers covering approximately 14 square kilometres of seabed in prime reef shark habitat.  The use of these transmitters allowed us to quantify the activity level, depth association and movement patterns of the Caribbean reef sharks post release and begin to understand how capture events might impact their behaviour.

The project officially drew to a close in November 2009 after taking blood from over forty Caribbean reef sharks and collecting approximately 33,500 detections  from the accelerometers attached to them.  The shark research team is currently collating the results which will be presented at the annual American Elasmobranch Society meeting in Rhode Island in July 2010.  The team will take part in a special symposium entitled The Physiological Stress Responses in Elasmobranch Fishes organised by Dr. Greg Skomal of Massachusetts Division of Marine Fisheries, and Dr. John Mandelman of the New England Aquarium.

An accelerometer attached to the dorsal fin of a Caribbean reef shark

An accelerometer equipped Caribbean reef shark just prior to release.

]]> http://www.saveourseas.com/blogs/cei-bahamas/2043/feed 0 http://www.saveourseas.com/blogs/sharkcentre-sa/2276 http://www.saveourseas.com/blogs/sharkcentre-sa/2276#comments Tue, 15 Dec 2009 07:34:21 +0000 Alison Kock http://www.saveourseas.com/blogs/?p=2276 The Save Our Seas Foundation (SOSF) White Shark Research Team together with the Shark Spotters tracked a 3-metre great white shark for 24 hours straight. This was the first successful overnight continuous track of a white shark in False Bay.

Studying white sharks along the False Bay coast. Hours of surveying is required to spot the sharks swimming inshore.

Following reports from the Shark Spotters of shark sightings close to shore within the last two weeks in False Bay, the Save Our Seas Foundation white shark research team headed out to survey the coast for sharks and attempt to tag one of them. They found a white shark at 12h42 on Tuesday 8^th December swimming along the surface between Seal Island and Strandfontein. After monitoring the shark’s behaviour for a few minutes the research boat slowly approached the shark to get a photographic identification of its dorsal fin, assign a catalogue number and determine the shark’s size and sex. After closer inspection it was determined that the shark was a 3-meter female, subsequently named Deepblue.

Collecting the dorsal ID of the 3-meter female white shark subsequently named Deepblue. Naming the sharks makes recording re-sighting information much easier in the field than remembering the complicated catalogue number.

Alison Kock, the white shark project leader with the SOSF and Shark Spotters, then tagged the animal at the base of her dorsal fin. The tag allowed the researchers to follow the shark in real time using specialized equipment mounted on the boat. “It is important to asses the shark’s behaviour while doing a track such as this in order to maintain the correct tracking distance; too far and the shark could swim out of range, too close and the boat disturbs her behaviour,” said Alison.

Alison tags Deepblue with a Vemco continuous pinger at the base of her dorsal fin. The tag emits a continuous signal which is used to track in real time.

Although the research team was prepared to track her across False Bay, Deepblue remained in the general area between Strandfontein and Seal Island. She was in no hurry to swim anywhere and her swimming speed varied between 2 – 4 km / hour. Deepblue spent a considerable amount of time at the surface and sometimes it appeared as though she was just drifting in the current and not actively swimming at all. Occasionally she swam within 200 meters from the coast before swimming as far as 4 kilometers offshore again.

Morne and Brocq (aka Maverick and Goose) take the first shift tracking Deepblue.

The team recorded interesting behaviour like this where a large yellowtail, Seriola lalandi, was seen swimming alongside the shark. PS. Look carefully between the pectoral fin and caudal fin to see the fish.

During the daylight track the team observed Deepblue approach another white shark of similar size at the surface. She slowly followed the second shark within 5 meters for a few seconds before breaking off the encounter and swimming in the opposite direction. Deepblue’s night behaviour was similar to her daytime behaviour, except that she went further offshore and also made some excursions in the direction of Gordon’s Bay and then towards Muizenberg, but always returning to Strandfontein.

“We did, however get an unforgettable surprise during the night, when bioluminescent plankton lit up both the ocean and the shark in a sparkling green glow,” said Alison.

A magical sunset in False Bay in the company of a white shark named Deepblue

No wind, calm waters, a sunset to take your breath away. This is what it's all about.

The research has previously documented the inshore behaviour of white sharks during summer. However, it is still unclear why exactly the sharks are present close to shore. Three predominant theories exist, namely 1) the sharks are predating on summer fish and smaller species of shark prevalent in the bay during summer time 2) environmental conditions such as warmer water or oxygen rich water may be what’s attracting them and 3) the inshore behaviour may be related to reproduction. Tracking the sharks in this way is a step towards determining the factors involved in inshore white shark activity.

The team would like to thank Dave Hurwitz of Simonstown Boat Company for assisting with the logistics of the track. Keep track of the team yourself when the next weather gap lets them track white sharks again at www.saveourseas.com.

Adrian and Brocq in good spirits even though we were all cold and starving during the night time track. Note to scientist - put food and coffee higher up on priority list next time around.

A spectacular sunrise in False Bay.

Additional information

The Save Our Seas Foundation White Shark Project was initiated in 2003 and is a dedicated research programme focusing on the ecology and behaviour of white sharks in False Bay, Cape Town, South Africa. It is collaboration between the Save Our Seas Shark Center, University of Cape Town, Department of Environmental Affairs and Tourism Marine and Coastal Management Branch and Shark Spotters.

Latest shark sightings

Muizenberg 10 December

St James 8 December

Muizenberg 8 December

Noordhoek 8 December

St James 7 December

Muizenberg 7 December

Muizenberg 5 December

St James 28 November

Muizenberg x 2 28 November

Muizenberg 25 November

Media contact

Alison Kock

White Shark Project Leader

Save Our Seas Foundation and Shark Spotters

Email: alison@saveourseas.com

Website: www.saveourseas.com & www.sharkspotters.org.za

A paper that is published in Marine and Freshwater Behaviour and Physiology reports the results of our attempts over the past years and shows that fed acoustic transmitters or sensors are viable tools to collect presence-absence data or physiological parameters of free-ranging sharks. What I found is that the minimum tag retention time ranged from less than 24 hours (bull shark) to 34 days (tiger shark), and bull sharks could be tracked for a minimum mean duration of 6.8 days. This is not a long time, but good enough to address some of the questions we try to answer. And as you can read in the paper, some of the bull sharks were double tagged with a stomach tag and an externally attached acoustic tag. We also attach acoustic tags externally to get longer tracks which helps to get information on presence-absence of individual bull sharks over a time scale of months or even years. I hope I can tell you more about these results soon. Keep watching this space!