Very sad, but I'm curious (educate me?).
Was this fish for certain hooked in a no-fish zone? If not, would the fisherman have known for sure what was on the line before he got it to the surface? Is it possible once he got it to the surface and saw what it was he may have released it knowing it was a protected species but not knowing enough to realize what had happened to the poor creature by bringing it to the surface? There are a lot of bumbling idiots out there.
Not sure which is worse, a jerk or a bumbling idiot, but the latter seems more forgiveable.