Marine Fisheries Resource Center
For Anglers: Releasing Fish

By NYSG's Mark Malchoff and Dave MacNeill

Why Release Fish

Releasing live fish is an important activity in recreational fishing. It will be necessary to release fish because of regulatory actions that are designed to enhance stock status in the medium to long term, for example, sub-legal sizes, closed season, moratorium, etc. Many recreational fishers practice voluntary catch-and-release of legally caught fish; examples include anglers who target black bass, striped bass and shark. Although recreational fishing involves many uncertainties and can also be a costly venture, there are many good reasons why more anglers choose to release live fish.

Catch-and release gives anglers a means of extending the fishing trip when there is a good catch rate of legal sized fish, or the angler has already achieved the daily bag limit. Catch-and-release has a positive influence on fish density; although a high fish density does not necessarily guarantee fishing success, many anglers appreciate areas where there is high abundance. Another important benefit that may be gained from releasing fish is its effect on population structure; fish population composition is very similar to unexploited ("virgin") stocks under these conditions, and there is a wide range of size classes. It is important to ensure that released fish have a good chance of surviving, in order for catch-and-release to be effective.

Hooking Mortality

Some critics of catch-and release argue that stress and wounding are often a lethal combination. This is true in some cases, however, catch-and-release mortality is species-specific and it depends upon many variables including the season, water temperature, tackle type, etc. Stress in fish causes physiological changes in the body; physical exertion (from the fight) causes a build up of lactic acid in the muscles. Acidic blood interrupts the normal metabolic functions and a fish will die if it is unable to restore its normal blood ph within a certain time frame. Lactic acid build-up is directly related to the length of muscular activity and it is better to have a quick retrieve and capture to minimize the damage to the fish.

Hook wounding is an important mortality factor that is also species-specific, being influenced by many variables including: wound's location, hook style & size, presence or absence of barbs, and lure type (artificial versus live bait).  Previous scientific studies identified the factors that influence hooking mortality.

  • Location: Greatest risk occurs in the areas of the gill and stomach; intermediate risk occurs in the areas of the lower jaw, isthmus and eye; lowest risk occurs in the snout, maxillary, corner of mouth and cheek.

  • Bait & Lures: Baited hooks result in greater injury than artificial lures. Fish tend to swallow live bait into the gullet near the gills, although it is possible to reduce this type of risk by using different angling techniques.

  • Hook Type: Wounds caused by barbless hooks are often less severe. Treble hooks often require more handling of fish by anglers, which prolongs the period when the fish is out of water. However, mortality rates caused by treble hooks are much lower than single hooks.

  • Metal: Fish are capable of rejecting hooks that become imbedded in the gullet or stomach region, although this process may take as many as 120 days. Scientific studies suggest that tin/cadmium hooks are rejected in a shorter period (60 days), however, they result in higher fatalities because of the toxic effects of the chemical breakdown. The mortality rate for stainless steel hooks is much lower in spite of the long retention period (>120 days).

  • Physiological Stress: Changes in physiology can result in higher mortality. Fish taken from depths greater than 40 ft may not be able to adjust to the changes in pressure or the difference in surface temperature. Depressurization causes bubbles of gases to accumulate in the blood and body tissue. Scales and mucous layers are used to protect the delicate skin, and any breach in the integrity of these layers provides an entry for bacteria and parasites.

    For further reading, please view "Hooking Mortality in Fish," an article by research scientist Suzanne Ayvazian, Ph.D. (click here)

Recommendations for Releasing Fish

  • Consider the trade-offs of using treble and single hooks, and act accordingly. For example, treble hooks may reduce the severity of the hooking wound, but fish hooked will require more handling and remain out of the water for longer periods. Treble hooks are a good selection if you catch small fish in cool water. However, if you catch larger fish in warm weather, it is probably better to use single barbless hooks because they are easier to remove.

  • Prior to fishing, use a pair of piers to flatten (or file down) the barbs on the hooks.

  • Develop a release strategy before you start fishing. Decide whether you will keep or release any fish before removing the fish from the water. You should also be familiar with fishing regulations and ensure that you have the necessary equipments for releasing fish.

  • When using live bait, take steps to prevent fish from deeply ingesting the hook; be attentive and set the hook quickly to prevent the fish from swallowing it. In the case of striped bass, experts recommend using trolled sand worms or drifted eels; "clam bellies" should be avoided because fish tend to swallow this bait deep into the gullet.

  • Reduce play time ("free spooling") of fish to a minimum. The longer the fish fights, the more likely it is to swallow live bait. Also, extended play time will increase the stress factor which reduces the chances of recovery.

  • Minimize the amount of stress by using a steady deliberate retrieve when the fish is hooked. This can reduce the amount of stress a fish undergoes when it is pulled from depths too quickly or when physically exhausted from an overly slow retrieve.

  • Decide whether to keep or release the fish as soon as it comes to the surface.

  • Avoid removing the fish from the water, if possible. Use needle nose pliers to pry the hook (lures only) from the fish while it is still in the water. Fish that can be lifted by the leader can easily be released over the rail using a dehooker. If live bait or lure is lodged deeply in the fish's gullet, cut the leader as close as possible to the fish's mouth.

  • If you must land the fish before releasing it, try to minimize the amount of time the fish is removed from the water, and any contact the fish has with hard surfaces and objects. Therefore:

Avoid using landing nets and gaffs, if possible. If you must use a net, avoid nets made from knotted twine because these will remove more scales and damage the mucous layer. Use a catch-and-release knotless nylon or neoprene bag, instead.

Handle fish with a wet towel, or use wet gloves to prevent excessive damage to the scales and mucous layer.

Minimize the handling and avoid touching the gills and the soft underbelly if you must handle the fish. Prevent the fish from battering itself on the deck or ground- you can use a wet towel or foam cushion. Covering the fish's eyes with a wet towel or glove also serves to subdue the animal.

Releasing fish is a delicate operation- gently place the fish in the water, head first while supporting the under belly.

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