Answer: World's biggest fish tale?

This wasn’t THAT hard of a problem, but I try to mix up the level of difficulty to both give you an idea of additional search skills and to make these challenges accessible to beginning searchers as well. 

For this fish tale, the easiest way to start would be to use Google Suggest to give you a few hints about where to look. 

So to begin, I just started my search for [ largest fish ] and then paused for a moment.  Google “Search as you Type”  kicks in and shows me a list of suggestions and a set of results for that query.  Note that all I did was pause, and the suggestions show up automatically. 

If you look at the 3^rd result, you’ll see something about a “whale shark.”  Curious, I click on that and quickly find the Wikipedia page which tells me that whale sharks DO grow to the claimed length.  12 meters?  Easy.  Girth of 7 meters?  Also easy.  

Here’s a photo taken of the coast of Peru that gives you the scale of the fish.  Since we know that whale sharks also frequent the coast of Belize, the size measurements seem VERY plausible.  (Here, the yellow dotted line is one scuba-diver length--say 7 feet or so). 

But we wanted to find some authoritative information.  A quick search in Google Scholar with the scientific name [Rhincodon typus] leads us to a ton of informative articles on the whale shark, their reproductive habits, and a description of the methods used to tell them apart.  (The easiest way turns out to be to take a picture of the spots on their backs.  Each shark has a distinctive pattern, like a fingerprint. See the paper below entitled: "An astronomical pattern-matching algorithm for computer-aided identification of whale sharks, Rhincodon typus.) 

And for finding a map?  The simplest way is to do the obvious search in Google Images for [whale shark map] which will give you a wide selection of maps to choose from. 

Obviously, you want to click through a few to find a map from a credible source.  (Which in this case is mostly just avoiding travel web sites, which tend to play up the whale shark presence in their neighborhood for eco-tourism reasons.) 

This map from the WhaleSharkProject is fairly typical, but it's so low-res that it basically suggests they live in the tropics.  While true, that’s not especially specific.  What if we wanted more precise data--actual sightings, for instance?  

Unfortunately, getting exact locations is a tougher job.  Distribution maps tend to be large scale. So to create a highly accurate sightings map, you’d have to aggregate multiple maps together.  And that's a job that’s a bit beyond the scope of this post on my Belize vacation!  If you create one, let me know and I’ll post it as an update! 

Search on!