If you're a spellcaster, I recommend holding a water elemental slayer spellbook when you toss the net, immediately start casting an area effect spell (chain lightning, hailstorm, etc. Don't use meteor swarm, though, as the spawn has high fire resistance) and target the spawn the moment it pops. Usually, this will eliminate all the water elementals in the spawn (as they only rarely have T-maps, it's not a big worry, and you can always use a boat to get to them later), and make the remainder of the spawn easier to deal with.