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Gear & Accessories

The Science Of Circle Hooks

by In-Fisherman   |  July 5th, 2012 0

The concept of a circle hook is almost as old as fishing itself. Archeologists have found ancient circle-style hooks made of reindeer horn in Japan, and similar designs of shell from Polynesia. In North America, Native Americans from the West Coast carved bone hooks that resemble some of today’s designs. Circle hooks are, however, one of the hot items in today’s fishing industry.

Demand has steadily grown from a base in marine commercial fisheries, particularly longlining, where baited hooks are set to fish passively. In addition to setting without rod action, circle hooks are favored in commercial fisheries because they hook and retain fish, even on slack lines. They also tend to hook fish in the jaw, causing less mortality than standard J-hooks.

Inland, trotliners and limbliners first tried circle hooks. Today, more anglers are experimenting with circle hooks for various species, based on their perceived benefits: Jaw hooking, which should make removal easier; reduced gut-hooking, resulting in less mortality; and easy setting of the hook, which would be ideal for inexperienced anglers and in deep water situations. Other possible advantages include fewer lost fish, fewer snags, and safer handling. Recently, fishery management agencies have recommended circle hooks for their conservation benefits. In a few situations, regulations even require circle hooks.

But what is a circle hook? This term has been applied to a range of designs, from models with a point that mildly turns toward the shank, to a true circle that snags nothing at all if placed in your pocket. In-Fisherman editors have used certain designs extensively in a variety of situations. We’ll continue to report our findings as we move forward. Overall, variation in design, along with lack of standardization of sizes among manufacturers, have led to conflicting results and confusion. We receive questions and reports about different designs and sizes for various species and sizes of fish, without resolution of any specific questions.

There’s been a similar rise in scientific studies of these tools, particularly their anatomical hooking position, degree of wounding, hooking success rate, and mortality. Dr. Steve Cooke and Cory Suski of the University of British Columbia recently published a major review of scientific findings on this topic.* They charted the increase in studies from 1996, when there were none, to 2004 when 15 were completed or in progress. They then reviewed the results of 43 separate evaluations of circle hooks.

Most have addressed marine fisheries, with striped bass the most common subject. That’s due to the huge striper fishery on the East Coast, where annual catch-and-release angling mortality has been estimated at 1.3 million fish, more than the number taken in the commercial fishery that year. Generally, the species most studied are those commonly captured on live or dead baits and those that have substantial hooking mortality with conventional hooks.

Cooke’s and Suski’s analysis resulted in some conclusions about circle hooks, along with many exceptions, further questions, and new areas for research.

Hooking Mortality: From a management standpoint, hooking mortality is critical when regulations require release of fish of a certain size range. And, of course, fish that are voluntarily released should be in viable condition. Delayed mortality can be important, but it’s far more challenging to measure. When results of all studies were lumped, circle hooks resulted in lower mortality than other types, mostly J-hooks and octopus styles. Mortality estimates for circle hooks ranged from 0 to 34 percent, compared to 0 to 46 percent for J-hooks.

There was substantial variation among species, however. For striped bass, mortality with circle hooks ranged from under 1 percent to 6 percent while J-hooks accounted for 9 to 18 percent mortality, a sizeable difference. Red drum, salmon, and tuna also showed major differences.

But in studies with bluegill and pumpkinseed, rock bass, largemouth bass, and summer flounder, mortality rates were similar between circle hooks and conventional designs (including octopus, sproat, and widegap). Bass mortality was low with circle (5.1 percent) and octopus (6.6 percent) hooks with fathead minnows as bait. Sunfish mortality was extremely low for all hook types (1 percent) and no rock bass were killed by hooking. For flounder, mortality for all hook types was between 12 and 16 percent.

Injuries and Mortality: Physiological damage from hook setting and removal can be minor or severe, including brain damage, blinding, and gill tearing. Cooke and Suski report that post-mortem exams of stripers killed with conventional hooks found damage to the heart, liver, gill arch, kidneys, and intestines. As circle hooks are not often swallowed, such damage is reduced. The summary of studies found that jaw hooking was far more frequent with circle hooks than other types. The incidence of gut hooking with circle hooks is low (generally less than 5 percent). Bleeding also was lower with circle hooks, a factor often related to hooking location.

Circle hooks did tend to cause more eye damage than other types, however. The point of some hooks tends to penetrate the eye orbit as it sets, and further damage may result from removal. Blinded fish are obviously far less likely to thrive, and the wound is a dangerous entry point for bacteria.

Time required to remove hooks can affect mortality, since fish are typically held out of water during the process. Cooke and Suski note that this factor hasn’t been examined widely, but that circle hooks generally were more difficult to remove. But again, this factor varies among fish species and likely also varies based on specific design and hook size in relation to fish size.

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