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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Over the past four years Rainer von Brandis has familiarised himself with a population of the usually timid hawksbill turtle in the Amirante Islands, Seychelles. This has allowed him to observe the turtles behaving naturally in their aquatic environment, revealing just how important they are for the maintenance of biodiversity on coral reefs.
The remote nature of Rainer’s study site, combined with a sound conservation policy in the Seychelles, means it supports relatively healthy turtle numbers. Consequently it has been possible to monitor how the hawksbill turtles function within a coral reef ecosystem outside of the relentless over-exploitation that has left them classified as Critically Endangered by the IUCN. Gradually, Rainer has been able to determine their prey preferences, how much they eat, their habitat requirements and even social interactions.
Reef fish lurk for scraps as a hawksbill turtle dines on sponge. (Photo: Rainer von Brandis)
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Enjoy a spot of golf whilst relaxing by the coast, or relish the swing from a boat deck? Ever lost the odd ball to the inky depths of the ocean in the process? Although it may seem inocuous, every stray golf ball out in the blue contributes to the considerable issue of plastic pollution.
Plastic debris, such as golf balls, does not usually biodegrade; instead it simply breaks up into ever smaller pieces. Even if it does degrade then its decomposition can release toxic chemicals into the marine environment. Much of the world’s plastic waste deposited in the oceans has become trapped in the North Pacific by swirling currents, covering an area reported to be more than double the size of Texas, forming what is now called the Great Pacific Garbage Patch.
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Sharks have wandered our oceans for the past 400 million years, which is at least 200 million years earlier than the dinosaurs and 396 million years before the first hominids evolved. They began to diversify about 330 million years ago, and since then these ancient fish have proliferated, occupying almost every niche in the oceans. At the beginning of the Jurassic period, about 200 million years ago, the first ‘modern’ sharks developed.
The great white shark is one of evolution’s top success stories. Streamlined, with two dorsal fins, a powerful vertical tail, a flexible jaw that can thrust forward to feed, and growing up to 6 metres in length, they are almost perfectly adapted physiologically, biologically and behaviourally to their ocean environment.
A white shark in Fish Hoek bay (Photo: Enrico Gennari / Copyright: Alison Kock)
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The Save Our Seas Foundation white shark research boat has been at sea today since early morning. Its mission is to track and tag the great white shark that was sited off Fish Hoek beach this morning. The tag will enable the team to follow the shark even when they cannot see it as the tag emits a constant transmission.
Coming Soon…
At the bottom of the ocean off Fish Hoek beach sits a radio telemetry receiver. This piece of modern technology works day and night in calm and stormy waters to gather information from swimmers by… Not your average passing fish, but great white sharks with Save Our Seas Foundation radio telemetry tags attached to the base of their dorsal fins. Located at several different locations across South Africa’s False Bay these receivers pick up the tags’ signals and map the movements of tagged sharks in the area. SOSF white shark scientist Alison Kock and her team will be diving out the Fish Hoek receiver at the first conducive opportunity. Stay posted for news on its disclosure.
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