MAKING INFORMED CATCH AND RELEASE DECISIONS
Anglers practicing catch-and-release in deep waters may sometimes have difficulty keeping their catch healthy for a strong release. Fish caught in deep water may appear bloated, stressed, or unable to swim down. These symptoms may be related to a phenomenon called barotrauma, a physical injury that occurs to fish that are rapidly moved from a high-pressure environment in deep water to a low-pressure environment near the surface. This article explores the fundamental concepts of barotrauma and discusses the effects of deep-water fishing on released fish.
First and foremost, everything in deep-water is under a considerable amount of pressure. In fact, the same pressure exerted on our bodies by the atmosphere doubles in 34 feet, triples in 68 feet, and quadruples in 102 feet of freshwater as an object descends. Biologically, fish are adapted to use a variety of depths, and base their selection on temperature, season, habitat type, and food availability. To move effectively across depths, adjustments are made in the amount of gas contained in a fish’s swim bladder to compensate for pressure changes.
The swim bladder`s function is to allow fish to remain neutrally buoyant in water, meaning the fish can suspend in the water column with minimal or no movement. Without maintaining sufficient gas volumes in the swim bladder, fish would constantly be fighting gravity and would waste energy trying to stay off bottom. Some species, such as the Round Goby, do not have a swim bladder, as they are adapted to live and forage on bottom. However, for most freshwater species, even bottom feeding fishes such as Lake Sturgeon and Suckers, remaining neutrally buoyant and being able to adjust depth selection provides advantages for feeding and movement.
THE EFFECTS OF BAROTRAUMA ON FISH
When fish are quickly moved from deep-water to the surface, as with angling, the swim bladder rapidly decompresses and expands in the fish’s body. This is called hyperinflation, the extent of which is dependent on the species captured and the depth it came from. The volume of the gas in the swim bladder will double every 33 feet (1 atmosphere of pressure) it ascends, which causes the swim bladder to expand and prevents proper swimming function. Symptoms related to barotrauma including bulging eyes, bloated abdomen, and gas bubbles formed in the blood and tissues. In severe cases, over-expanded swim bladders can also force the stomach to exit the mouth through the oesophagus.
These symptoms can cause significant internal damage to a fish; additionally, the buoyancy caused by the inflated swim bladder may force fish to remain at the surface post-release where they are vulnerable to thermal stress and predators.
MOST SYMPTONS NOT VISIBLE
Other barotrauma symptoms are not readily visible to anglers; these include internal bleeding, blood clots, as well as compression and bruising of internal organs. Internal injuries like these can cause behavioural changes that impact feeding, spawning, or predator avoidance. The effects of barotrauma may lead to delayed mortality even if a fish swims away after its release. In moderate depths (i.e. 20 to 30 feet), good handling and a quick release should cause few issues, but extended handling and stress will worsen even mild barotrauma and potentially lead to a poor release. In many cases, severe barotrauma is lethal to fish if left untreated.
WHEN IS BAROTRAUMA A CONCERN
Anglers may then ask: what depths should I avoid to make sure I can release my fish? That answer is largely dependent on the species you are targeting.
There are two major types of swim bladders found in sportfish species: these are physostomous (open) or physoclistous (closed) swim bladders. Fish with an open swim bladder have a pneumatic duct connecting the swim bladder to the oesophagus, which allows them to belch excess gas in certain cases to decompress. Anglers targeting Lake Trout, catfish, and sturgeon often observe this behaviour.
Fish with closed swim bladders can only expel gas through the gills via the bloodstream and therefore cannot regulate excess gas quickly as the process may take hours. Species such as walleye, bass, crappie, and perch are then susceptible to barotrauma in depths exceeding 25 ft, with severe cases occurring more often in depths exceeding 30 ft.
A study on the St. Lawrence River conducted by the State University of New York found that the incidence of barotrauma increased to 50% for Walleye, Smallmouth Bass, and Yellow Perch caught in 10 m (32.8 feet) of water.
Furthermore, another study run by the Ohio Department of Natural Resources on Yellow Perch in Lake Erie predicted mortality as high as 95% for perch caught in 60 feet of water. However, symptoms can occur in shallower waters for some species as shown in a 2020 study that investigated barotrauma during ice fishing for Black Crappie and Bluegill in Shadow Lake, Wisconsin.
McKendree University researchers found that 50% of fish captured exhibited signs of severe barotrauma when caught in depths of only 20-23 ft. This has important implications for delayed mortality if a fish is unable to escape surface ice when released under the hole.
AVOID FISHING DEEP WATER
The best way to prevent barotrauma related mortality is to avoid targeting fish in deep-water, particularly species with closed swim bladders (see species list). It is important to note, however, that species with open swim bladders are still vulnerable; the main difference is that they maintain the ability to return to their capture depth if they expelled gas but does not guarantee this behaviour will occur. For this reason, when fishing for species such as Lake Trout, use caution when fishing in depths exceeding 70ft, as internal injuries will still happen. This despite gas bubbles being released during the fight, so proper handling and minimal air exposure are very important for these fish. Additionally, the mechanism that allows fish to ‘burp’ during the fight is not entirely reliable, and some Lake Trout cannot release gas and thus will have more severe barotrauma symptoms.
WHAT ARE THE TREATMENTS FOR BAROTRAUMA
In the past, there have been many treatments tested on fish to relieve the negative impacts of barotrauma. ‘Fizzing’ was used to quickly remove excess gas from a fish’s swim bladder with a needle and syringe so that it could submerge. This technique is not recommended for anglers as it can cause a suite of other complications to fish, such as infections and punctures to other internal organs. Fizzing requires very specific training and tools to minimize damage.
More recently, descending devices are becoming a popular method to treat fish with barotrauma. These are employed in many deep-water saltwater fisheries and are now legal requirements to have onboard for some jurisdictions.
The concept of a descending device is simple: attach the fish to a weight and sink it to depth of capture. Descending devices can be purchased commercially or made at home.
The key is to keep a device in the boat amongst your release tools and if you ever notice a fish has the external indicators of barotrauma (unable to descend, eyes bulging, bloated, stomach pushed through mouth) then you can quickly attach it to the device and descend. The general design is a hook or grip attached to a fish that is rigged to a weight and a length of line. The angler quickly attaches the fish to the line, descends the fish to the depth it was caught at, detaches the fish, and hauls in the line. This allows the fish a chance to recover at the correct depth, but this technique should be preformed quickly and carefully to minimize additional stress.
Preventing barotrauma related mortality
Good catch-and-release practice protects our fishery resources at the population level, and it is important for anglers to learn and share information on the risks associated with deep-water fishing and barotrauma. The old saying, ‘an ounce of prevention is worth a pound of cure’, applies to barotrauma given that anglers choose at which depths they target certain species and can actively prevent the risk of barotrauma. For those that have accidentally caught fish in deep-water as bycatch (e.g. Walleye or pike while Lake Trout fishing), having a descending tool onboard can help improve that fish’s chances of surviving to grow and be caught again.
Tips to avoid barotrauma during catch-and-release
- Avoid catch and release fishing for the species listed below in waters deeper than 30 ft
- When fishing for trout species or other species with open swim bladders, avoid extreme depths (i.e. over 70 ft) and be sure to practice responsible catch-and-release practices
- If you are releasing a fish with severe symptoms of barotrauma, do not fizz the fish! Get a descending device and know how to use it
- Do not play fish slower to let them “acclimate”, it is best to fight them quickly and rapidly return the fish to the water while it has more strength to submerge
- Do not keep fish with barotrauma in a live-well to recover, release or descend them as quickly as possible
Sportfish species not recommended to target in deeper than 30 feet
- Percids (Walleye, Sauger, and Yellow Perch)
- Centrarchids (Smallmouth, Largemouth, Bluegill, Black Crappie, Rock Bass)
- Coregonids (Lake Whitefish, cisco)
- Esocids (Northern Pike, muskie)
- Burbot