I'm no expert...so my observations are purely conjecture....but I read everything I can concerning ancient arrows (and other projectiles).
If you are at a site doing a lot of fishing, crabbing, clamming, and crawdading, seems to me like you be more apot to be using a lot of short handle hafted knives for wood working of racks and what not.
Well, if you've done some crabbing, clamming, and the like (I grew up in NH) then you know that the harvesting is tide-related. If your site has no tides, then they might have been doing more hunting than fishing. In any case, simple wooden tools and strong cordage is all that is needed for "aquatic resource collection".
I seek the opinion of those familiar with projectile based hunting. I have read a theory that the contracting stem was a hafting adaptation.
In some cultures, the shape of the projectile points was influenced, at least in part, by spiritual symbolism. For example, many cultures living near the sea made points that resemble the teeth of sharks. In your case, the shape more closely resembles the shape of gar scales. Point is: hafting considerations are only part of the story.
That said, a point with a contracting stem is very good at resisting impact shock. The stem acts like a wedge and the binding actually gets tighter when force is applied to the tip. The fact that the point might easily slide out of the hafting (when the dart or foreshaft is pulled out) is probably a drawback...not an advantage. The users of the points you have were probably trying to pentrate something with a hard skin or tough covering. Things like turtles, very furry creatures, or even enemy shields.
Which leads me to my last thought: looking at just the hunting aspect leaves out one very big thing: WARFARE. The site you are digging at seems to be very productive. There would be many challengers to anyone who would try and set up a permanent residence in such a prized location.
