Wide circle hooks appear to reduce the capture of turtles if the hooks are wider at their narrowest point than J-shaped hooks, tuna hooks, and teracima hooks, making it difficult for the circle hook to fit inside a turtle’s mouth. Furthermore, circle hooks are circular, with the point turned perpendicularly back toward the shank, less exposed in comparison to J or tuna hooks. Thus, if a turtle does bite a circle hook, they are less likely to be deeply hooked (where the hook is swallowed down the throat or pierces the roof of the mouth), making dehooking easier.
Shark catch rates are higher on circle hooks relative to J-shaped hooks, but at-vessel mortality rates are lower. This is because animals caught using circle hooks are not hooked as deeply, are less likely to suffer internal injury, and therefore have a higher likelihood of survival.
In fisheries where sharks are not retained, there will be a higher shark fishing mortality on circle hooks. However, the benefit of very large reductions in marine turtle catch rates on wide circle hooks may outweigh the tradeoff of increased shark mortality.