Me and a rogue budy (67 cleric + 54 rogue) camped these no prob. We zoned in at the camp, swam out and around (ocean side) and just swam down the river. You'll get about 10-15 of these a trip. Would guess 30 min spawn timer, but we didn't time it, or even watch, so could be sooner. NO NOT LET THEM GO ABOVE THE SURFACE!!! We had a good 5 mobs disappear on us like that. keep them well under-water or they just poof, still alive, and still targeted. Took us about 3 rounds of the 10-15 mobs to get all 4 raw's.
Suggested you have high swimming skill, makes it alot easier. 200+ would be best.