Ocean Finfish Landing Net Size Requirement

It's not big enough for a salmon or halibut.

Do you think it contain/control a salmon or Hali?  Interestingly, these seem very much like a collapsible & floating version of a cheapo crab ring, which I have considered trying out for this very purpose (they are very big and nice and deep).

For halibut, use a gaff.

   I went through the regs quite a few years ago and found out that for some nets, other than landing nets, the regs specify the kind of hoop and handle required.  So the rule-writers knew how to require it, but didn't when it came to landing nets, so my conclusion was that landing nets don't have to have a hoop or a handle - just a opening with a diameter of 18".   
And I rolled up a net with a large opening made of thin strings and stowed it in the pouch on the back of my kayak seat, so I always have a "landing net" even if I forget the one I normally take that has a hoop and handle.   I just don't have much desire to be a "test case." - I'd rather be fishing.
    (Rant warning:)Aside from amending the regs about open reserves, etc., seasons, size, bag, and possession limits, CA fishing regulators don't seem to make many changes to the rules over the decades, and the result is just about the most confusing set of regulations possible to imagine.  Cynics would claim that's done for the purpose of maximizing revenue or facilitating warden arbitrariness , but I suspect it's more about poor management or lack of funding for qualified help to re-write the regs. so the average angler could understand them.
   

Washingtons regs are just as bad as California.

That looks great, but kinda pricey...

I keep a mesh, drawstring laundry bag in my center hatch as my "back up net." The opening is about 24" in diameter.  It meets the letter of the law.  Its main purpose is to keep me in compliance in case I lose my net in the water or I forget to bring one with me.

I believe I picked it up at either Walmart or Target for under $5.
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I do something similar

https://cdn.shopify.com/s/files/1/0648/7791/products/dive_bag_yellow.jpg?v=1414369352