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.

Aligned Ore
Blue Diamond
Chunk of Taelosian Rock
Nilitim's Grimoire Pg. 116
Raw Crimson Nihilite
Raw Dark Matter
Raw Squid
Rune of Attraction
Sample of Taelosian Sludge
Sapphire
Shell Inlaid Collar
Taelosian Tea Leaves
Taelosian Wheat
Talisman of the Spiritseer
Tears of Prexus
Yellow Tide Feaster Bile