35 shaman just finished this quest.  It is very doable as a 35.  The map coords farther up in this thread is very good. The hardest part for me was getting to Nagle. Tried the run from Brackenwall Village along the mtns - aggroed lots of spiders, crocs, slugs, and died a couple times before I made. The second trip followed the road out of Brackenwall, went north to where the road came closest to the water and ran to the coast without any trouble. Then ran south along the coast all the way down to Nagle's island. Only a couple short spots where you have to swim and very few mobs.

Fishing spots
Desolace - right outside Shadowprey village (3 casts)
Feralas - take road west from Camp Majache - just past the bridge over the Vedantis River there is a bank on the right (10 casts)
STV - go up the coast a little ways until it turns into Savage coast, avoid crocs (3 casts)
Swamp of Sorrows - gotta make the run from Stonard to the eastern coasline, stay close to the hills, skirt the spiders (ghost wolf form helped me outrun them) and then turn south at the coast, avoiding the murlocs and crocs. Tooke about 15 minutes worth of casting here for me.

Make sure that after you return to Nagle to complete quest that you fish right there with him until you go from 225 to 226 skill (about 7 casts), Then you can stone out.