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.
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Cheryl-Samantha Owen reports from Day 2 at the Sharks International Conference in Cairns, Australia.
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.
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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!
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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.
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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 8th 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.
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