You don't need to go to the starting co-ordinates, unless you are interested in fishing.
The fish we are interested in is closer the the parking area (out of the water), and a LOT larger.
The Seychelles Blenny is a cryptic fish - how could you resist that for a puzzle!
The reasons why it is a cryptic fish is explained on a small sign, although I somehow doubt they really apply here. But it is worth reading about it.
To locate the Seychelle's hide, you need to go to:

Note: please leave the stamp in the cache, it is not a swap.