With the warm ocean temperatures, there could be alot of things out there that we don't normally see - King mackeral, wahoo, cobia, numerous species of shark, etc. Could have been almost anything.

Here's what it probably wasn't:

Seals - they breath air so it would have surfaced immediately if stressed.

Tuna - There might be some around but if you hooked even a small bluefin or yellowfin, it would have completely spooled you in about 10 seconds. Or less.

Chinook salmon - Even a huge one would have fought alot like a smaller one. That is, a series of headshakes, several long panicked runs, and the usual rolling and twisting. Your description doesn't seem to fit.

My guess - Shark.