I found some info that suggests you can buy some supplements that can be added to their food, or inject Lugol's iodine in a certain amount (1/2ml/week) into their food.
Here check this link out:
http://www.wetwebmedia.com/results.html?cx=partner-pub-4522959445250520%3Ap7g47g81naq&cof=FORID%3A10&ie=I SO-8859-1&q=Sharks%2C+goiter%2C+iodine&sa=Search&siteurl=w ww.wetwebmedia.com%2Findex.html
Its got a few articles on iodine info in general, iodine with sharks, shark disease, etc...
Bob Fenner is one of the respondents so its good info.
Hope that helps,
Chris