Easily the most eco-friendly way of putting fish on the dinner table is spearfishing... Sadly, spearfishing has many adversaries who have spread a lot of propaganda that makes far too many people believe just the opposite. As a result, there is both a certain social stigma as well as far too many anti-spearfishing laws.
The big advantage of spearfishing is that it is a selective means of harvesting fish while, on the other hand, hook and line, nets, and fish traps are not. With spearfishing there is no such thing as by catch or damaging a fish you do not want to catch.
For the record, I never ever spearfish in places where it is illegal, nor am I suggesting that folks on sailboats should ignore such laws (even if they are dumb laws). I am simply pointing out that if you actually think through the various processes of fishing that spearfishing is easily the most green and eco-friendly method available to us.
Lately, I have been reconsidering the use of spearguns in general, because of the bureaucratic hassle factor of having a "gun" onboard the boat. Some places require you to bring your spearguns to the police where they will keep them for the duration of your stay. Which becomes all sorts of problematic if you want to leave from somewhere other than where you arrived. For those folks who think that hiding their spear guns is an option that makes sense, there are two words you should keep in mind... Fines (as in huge) and inmate (as you may very well become one) to help you keep things in focus.
Most places that have unreasonable anti-spearfishing laws seem to ignore triggerless (hand spears and Hawaiian slings) spear fishing gear. But even in places where they are not allowed, the price of triggerless gear is such that you could lose it and replace it later for a fraction of the cost of a quality gun.
The downside of triggerless gear is that it takes quite a bit more skill and is very much more up close and personal than using a spear gun. For those of us who seldom even think of eating reef fish (can you spell Ciguatera), it is still early days in terms of technique and gear to go after pelagic fish species (Mahi Mahi, Wahoo, Tuna, etc) with a hand spear instead of that Tuna gun!
More on triggerless set-ups next...