With regards to the Speargun #1 and #2 attacks, it appears to be a level scaling issue. Hop in the water in Cursed Shore (Level 80) and the tooltip reads
Damage: 62
Bleeding (4s): 194 Damage
Go just out the gates into Gendarran Fields (effective level 30) and your tooltip reads
Damage: 62
Bleeding (4s): 70 Damage
Somewhere below 30 it starts scaling properly, as in the harbor at Wizard’s Fief (effective level 20) you get
Damage: 55
Bleeding (4s): 47 damage.
I noted some inconsistancies with other speargun skills, too. For example, Mercy Shot shows 498 Damage in Cursed Shore, but 521 at an effective level 38 in Lornar’s Pass, 531 at level 48 and 526 at lvl 56 in Bloodtide Coast, 516 at lvl 66 in Sparkfly Fen, and 506 at lvl 74 in Straits of Devistation.
(all with the same gear equipped)