Here's why:
* Scientific names are always capitalized. This applies to the genus name ("Galeocerdo") and the species name ("cuvier").
* Common names are often capitalized when referring to a specific species. This is because "Tiger Shark" is a unique name for a specific type of shark.
However, you wouldn't capitalize "tiger shark" if you were talking about any shark that resembled a tiger, or if you were using it as a general term.
For example:
* Correct: "The Tiger Shark is a dangerous predator."
* Correct: "I saw a tiger shark while snorkeling."
* Incorrect: "The tiger shark is a dangerous predator."
* Incorrect: "I saw a tiger shark while snorkeling."