Hook Size: Though there are general guidelines, it's often impractical to use hooks to match the expected size of fish. Large circle hooks don't hook small fish efficiently, and there's evidence that small circle hooks are more likely to hook larger fish in the gullet. This was evident in a study with sunfish. Larger circle hooks also may cause more eye-hooking of small fish, though they don't hook small fish efficiently. Obviously this is a vast topic, involving the nearly infinite range of fish sizes and the many hook styles and sizes.

Offset and Non-offset Designs: In describing hooks, “offset” refers to the amount of deviation in the plane of the hook point relative to that of the shank. In studies of sailfish and striped bass, offset circle hooks caused more damage than non-offset ones. But this result has not been consistent. It appears that the degree of offset (15 degrees is considered severe) affects rate of damage and mortality. A recent study on walleyes found no difference in deep-hooking between non-offset and 15 degree offset circle hooks, however. Jigs were less likely to deep-hook walleyes than octopus or circle hooks (#4 Mustad Demon Circle Fine Wire) fished with leeches and crawlers.

Hot Topics: Cooke and Suski report that flies tied on circle hooks are a hot item, due perhaps to the conservation bent of many fly fishers. Preliminary results suggest, however, that circle hooks were not as effective at landing trout and bluegill as J-hooks, and removal time was greater. Bleeding and tissue damage were similar between hook types.

Sucker fishing for muskies in cold water continues to be popular in a few areas. This technique causes high mortality by stomach-hooking, when anglers allow muskies to swallow the hook. There's no data on use of circle hooks yet, but conservation benefits seem likely. Then again, perhaps single hooks of any design might compare unfavorably with the use of tandem treble hooks rigged in quick-strike fashion. One can only guess, based on personal observation.

Only one unfinished study has addressed circle hooks for ice fishing. As might be expected, trout were hooked deeper on J-hooks than on circle hooks, but mortality figures weren't available. Further benefits or drawbacks of circle hooks for ice fishing remain unproven. Gut-hooking of pike and walleye on tip-ups might be reduced with circle hooks, provided the hooks turn and set under firm hand-pressure on the line. Here again, quick-strike rigs have proven to reduce the incidence of gut-hooking while increasing hook-up percentage.

Trotlines and limblines fished for catfish are well suited to circle hooks. Opening the gap a bit on full circles has provided better hook-up ratios in some situations, though again, differences among hook types affect results. Open gaps also make it easier to bait hooks. Overall, circles hook and hold fish well and reduce mortality considerably, important as more length- and bag-limit regulations are enacted. But again, personal experiences also suggest that eye damage is common when circles are used on setlines.