What did the line look like at the break? Curled? - like it broke at the knot? Tie carefull knots and be sure to lube up your line (saliva) before cinching the knot down tight. If it's a real clean cut it could be sharks. If it's frayed/rough could be salmon teath - check your leaders after every fish. I'm jealous that you're there and I'm here. I'd much rather be loosing fish than loosing sleep working a deadline at the computer.

Tight Lines!!
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. . . and God said unto them, Be fruitful, and multiply, and have dominion over the fish of the sea . . .