Hey, I finally figured out what wolfram|alpha is for:
How large must the helium ballon be?http://www65.wolframalpha.com/input/?i= ... ters%29%29
It took me forever to figure out how to phrase that so that wolfram would understand though. And it refused to do the cm^3->m^3 conversion automatically. But, hey!
Except that it gives a rather large answer... 2068 m^3. Apparently Wolfram thinks the typical weight of a maneater shark is 2268 kg. Wikipedia says "A typical adult great white shark ... has a mass of 680–1,100 kilograms", so this seems extreme. Using bull sharks as previously suggested (Wiki: "Bull sharks are large and stout. Males can reach 2.1 m (6 ft 11 in) and weigh 91 kg (200 lb). Females can be much larger:up to 4 m (13 ft 1 in) and 318 kg (700 lb).") would help - if we take a male bull shark we can get away with, say, 85kg as the weight, so we'd only need 77.5 m^3 of helium at atmospheric pressure.
Though when I tried Alpha with a bull shark, it promptly substituted a Swan River whaler and gave me a range of 82.05 to 209.7 m^3. Amusingly, it gave me an option to use a Bluntnose six-gill shark instead, but when I tried it, the result was "Insufficient data available".
In any case, the helium still has to be pretty amazingly pressurised to fit in that little tag. And it does raise the question of why the scientists would be putting enough helium in the tags to lift the entire shark rather than merely enough to lift the tag. Any tags that do pop out properly aren't going to be landing for a long time.