Thats kind of funny Spawnout...
I have had the exact opposite experience... never have had a seal grab a fish I was fighting, but I did have a sealion grab a 30+ pound king at sekui... ( Long story there but I did get the fish after doing what you said keeping the boat over the beast so he couldn't come up for air...)

I have had seals hook up on herring though... Gotta thumb that spool quick cause those suckers can fly under water....

Me thinks you're just not catching big enough fish... :p