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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In principle, there are two ways to equip sharks with acoustic tags: you can either attach the tags externally or internally. For both methods there are good examples to be found in the scientific literature. If done internally, you would usually catch the fish for surgical tag implantation. An alternative method can be feeding acoustic transmitters to sharks. 
Stomach tagging can be an interesting option and it allows you to, for example, monitor the stomach temperature of the animal in addition to obtaining presence-absence data. However, the indigestible tag will eventually be regurgitated, most likely via stomach eversion, and therefore tracking time is limited. In order to feed a tag to a shark, all you need is the tag wrapped in bait and a site where you know you can attract the sharks close enough to a feeder. There’s no better place than the Shark Reef Marine Reserve in Fiji to test the feasibility of stomach tagging and to estimate tag retention time. And so we did. The superb photograph on the right (taken by Klaus Jost) gives you an idea of how it looks when you hand-feed a tag to a good-sized bull shark in Fiji.
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