Make a big, long conical basket that you can put in the water. The size of the meshes determines of the size of the fish you want to be able to escape. Make a wide input funnel which is very narrow and the fish leds to the basket. Lay or hang some bait. Or hunt fish in the right direction. (With an appropriate trap you (catch bait,) flies, mice,...)

fuikenIn order to avoid that caught prey ((too) easy) escapes again, you can make on sufficient distance two or three funneled entrances in succession.

You can also build a similar fixed structure in a river with stones and branches.
Or you can make it in a tidal (lagoon...) so there may enter fish at high tide, but at low tide cannot get out anymore. This can of course also with nets. So traps and fykes can vary from the size of a jar or bottle, up to a lagoon.The oldest structures on Earth, more than 30,000 years older than the Pyramids of Egypt, are the Aboriginal's 40,000-year-old fish traps on the Barwon River (Brewarrina Shire, New South Wales, Australia). The stone walls stretches in trap shapes form a network of about half a kilometer along the river bed.

Have you eaten whale? Yes. Is much he?