How do spearfishermen ensure legal size fish?

I mean, after you shoot it's too late...

The beauty of it all is being responsible for your actions. You know before you shoot.

For some fish there's no easy way to ensure they're legal.  The short answer is "experience", but here are some things I did to build that experience. 

Water magnifies, but you can look and then feel things to gauge true size.  You can use rocks, kelp or your own equipment as a control group. 

For fish, start shooting those fish that don't have a minimum size, like perch to start getting a feel for guesstimating length.  You can put some tape on your gun or polespear to measure the perch afterwards.  That will tell you how close or far your guess is from actual length.  After some practice you should be able to guess pretty accurately the size of a fish as it swims by a certain rock or kelp. 

There will be other fish that are more difficult to gauge.  A lingcod in a hole where you can't see the entire length, or a halibut that's mostly buried where only the eyes or it's jaw is visible.  I think lingcod are a little easier as you can get fairly close as well as usually having more time to look at it relative to it's surroundings.  For buried halibut, you can look at the distance between the eyes or how far the jaw extends (if you can't see the outline). 

Certain species also have certain parts that develop as they get bigger/older.  Some fish will have a hump (some call shoulders) just behind the head/gills.  Some species may develop particular coloration or patterns.  While others just swim differently.  I call it the big fish swagger because of their size or age, and they just appear to be swimming more assuredly. 

It's a good idea to read up on the species you may encounter and get an idea of max. size, what they look like...etc

When in doubt, don't shoot. 

Mooch and Angle only shoot fish with no size limits.....hence the stringers of perch.

It's a fact that things underwater appear magnified.  If I remember right I think it's a 1.25 factor meaning a 19 inch ling would appear to be 24 inch.  Quite a difference.


when in doubt, don't,

I used to use my pneumatic gun as a gauge, it was about 24 inches, so it gave me an in hand reference.

Practice discipline when hunting. Don't shoot stuff that barely makes the size limit. Practice holding your shot until you can make a clean head shot, don't shoot a fish unless you can tell what kind it is and don't take 7" abs. The headshot is a personal thing for me that I just try to do for the challenge. The rest will not only keep you out of trouble but it will make you a better hunter.

None of this matters anyway becuase I don't think we will ever see diveable conditions again. I've been waiting for almost 2 months now to get back in the water.

First ling I speared was 21.5" (legal was 22" then). I threw it back (dead). I've never shot another undersize since. If it doesn't look WELL over 24" I don't shoot it. Sometimes I pass up one that I can only see a head, and as I'm sussing it out it turns and flees and I see that it was actually a 30 incher. That's much better than the opposite.
I've shot every halibut I've ever seen except one that was obviously too small, and never got an undersize (a couple 23"). that is because around here they seem to be plenty legal. Last year there were many just-legals though, so I'm gonna be real careful. It would kill me to spear an undersize halibut, as they are my favorite fish to hunt. I only take about 3 a year (if I'm lucky), and I would hate to kill next year's fish!

Good info thanks guys I had the same ?'s