Porpoise harassing

[sprange]

Two nights ago while watching the sun set into the mountains I noticed a pod of porpoises swimming by perhaps a hundred meters off shore (one of the joys of oceanfront living). In pursuit were two large yachts and a much smaller boat. The boats eventually caught up and I swear that the operator of the small boat had something that appeared to be a speargun. I was too stunned to actually view with my telescope, but from what I could tell nothing came of it. The chase eventually continued out of view. The 'weapon' that I saw could just as well been a fishing rod (most likely). Do porpoises often follow a school of fish? I accept that the pursuit could have been because the boaters found the fifteen or so porpoises interesting to watch (as I did while sitting at my computer) but the guy with the rod/speargun/etc bugged me. Do people poach porpoises or perhaps do the porpoises indicate a fertile fishing location?