Here's a technique for bleeding a halibut that might be useful to consider on a kayak. I fish with a small short-bladed emergency flip knife on an elastic lanyard around my neck that is easily accessible for this purpose.
You can usually see a natural mark or seam in this section that lines up with the pectoral fin behind the gill plate that is easy to punch and follow.
I started this clip at :45 and the point about bleeding stops at 1:25, before going on to filleting technique.
https://youtu.be/yviDaE5FO8Y?t=45s