Greetings from the striped bass-laden coast of Maine, where, having just been skunked during the morning low tide, I was left to ponder the many differences between fly fishing for trout in a river, and fly fishing for various species in the ocean. (What a difference three days makes.)
I have decided that, while we basically use the same gear--long rod, simple reel, and weighted line--to do both, that's pretty much where the similarities end. Saltwater and freshwater fly fishing are two different sports, done with similar tools.
For example: In freshwater/river fishing, your cast matters almost zip, nada, squadoosh... while in saltwater fly fishing, you aren't even in the game unless you can huck it 60 feet or more. Usually more.
In trout fishing, you must present your fly delicately... spoon feeding that insect pattern right toward the fish; In the salt, fish aren't used to their dinner attacking them... the fly has to move nervously, away from the fish.
Birds over a river... bad sign for trout fishing; birds crashing a salty flat... get your (behind) in gear and cast right there.
Hook at trout, rod tip up; hook a striper, rod tip low... you let the rod abosorb pressure when trout fishing, and you apply pressure through the line when saltwater fishing.