It's easy to envision: A sleek swordfish, many meters long and massive, flaps its powerful tailfin, rapidly accelerating through the ocean water at breakneck speed, until it spears its helpless prey.

I first saw the swordfish at 7:50 a.m. about 12 miles off the coast. He was 50 yards away, swimming kind of erratically and slowly. He was so big that I was a little afraid of him at first. I figured ...