Survival of Deep Water Caught Rockfish

This article may well bring out differences of opinions on how to take care of the barotrauma problem encountered on releasing fish with swim bladders. Fish get the Bends just like divers do as the nitrogen in the swim bladder expands as the fish are brought to the surface. About 30′ seems to be the magic number where the water pressure STARTS to re-compress the air bladder. This pressure multiplies in increments the deeper you go. The volume of a fish’s swim bladder can triple when reeled in from depths as shallow as 100′.

Every rockfish has a gas-filled organ called a swim bladder that allows the fish to gently control its buoyancy. By deflating its bladder, a fish can descend more easily. By inflating it, its ascent is assisted. When a fish is caught and reeled in, the fish can not adjust fast enough. Depending on the depth at which the fish was caught, a fish’s air bladder may swell so much its stomach is forced out its mouth. The eyes may bulge and other organs can be injured as well. Fish suffering from pressure-related injuries are said to be experiencing barotrauma (pressure shock). Without intervention, a fish with barotrauma may die from the progression of its wounds or succumb to temperature shock or predators

There are more than one method of allowing these deep caught fish to redescend so that they survive with minimal chance of mortality, either by the act of venting or descending them. Below will be 3 methods that can be used effectively.

However possibly along with these, there needs to be a CONCENTRATED effort by the WDFW to inform the saltwater fishing public as to ways to (1) avoid the situation or (2) handle it in a manner whereby these fish have a good chance of survival. This has been done on salmon, now is the time for Yelloweye, Canary and other rockfish. Here is a link to SAVE OUR YELLOWEYE.

Handling the Catch : When you get a fish alongside the boat that you are planning to release, take a moment to assess the situation for potential hazards, including the location of the hook. Many small fish (under 10# ) if hooked in the jaws can be lifted directly onboard if the line is sufficient weight. If you need to get a hold of many inshore species, such as most bass & rockfish, the lower lip is the first apparent place to use as a lifting location. This is a safe technique if the species has relatively small, plate-like teeth, and obviously not a safe idea for toothy predators, like lingcod. Jaws of most fish are relatively strong and can support the weight of the body and provide an excellent handle for immobilizing small quarry.

Many fish, will temporarily cooperate when grabbed firmly behind the operculum (gill covers). Care must be taken not to damage the gills, as they are the primary site of oxygen exchange and are extremely fragile. Gripping the fish behind the head will typically cause the fish to cease moving and open its mouth for easy hook removal. It is important to apply firm pressure to initially grasp and keep the fish under control, while being careful not to squeeze so hard that you damage the underlying gill filaments. Inserting your fingers beneath the gill cover is not recommended because even the slightest brushing of the gills could cause them to bleed, further increasing mortality.

One thing that most people usually associate with handling fish is the slime layer coating the skin. What is often not considered is that this slime coat is essential for protection from bacterial infections and also assists in the maintenance of internal salt balance. To prevent stripping your catch of its much needed slime coat, it is important to either gently cradle your catch with a wet hand or chamois or firmly grasp it around the operculum. Often, the proper use of a release tool will allow you to completely avoid contact with the skin, leading to a very clean release. Also, when a landing net is required, it should be constructed of soft nylon or rubberized material with knot-less mesh to reduce the loss of slime as well as minimize fin damage.

Another problem associated with decked fish is the effect of gravity. Many fish species do not have the internal support structures needed to offset being lifted out of the water, this is especially the case with large fish. Gravity experienced while on the deck may be enough to severely damage internal organs and stop blood flow. This is why it is not a good idea to remove really large fish from the water, even if you feel the photo opportunity calls for it.

Releasing the Catch : A variety of release tools are commercially available to reduce the likelihood of handling injuries to both fish and fishermen; however, you can usually construct an effective device in your own garage. Extended hook re-movers, lip-gripping tools, line cutters, tailers, and fish descenders can all be effective if used properly under the right conditions. If your plan is to release the fish, it is always critical that these tools are ready and easily accessible, since much of the stress and injury to the fish occurs when the fish is at the boat, waiting to be released.

Every bottom fisher should have a fish-descending tool on board to assist in sending small or prohibited species back to their deep-water habitat. While there are some good commercial products available (such as the Shelton Fish Descender or the Git-r-Down, an inexpensive and quick way to effectively sink floating bottom fish is to have a separate rod rigged with an inverted barbless hook affixed to a large sinker. The barbless hook can be pinned through the corner of the mouth and the fish brought back to depth relatively quickly. When you retrieve the rig, the inverted hook will pop free and the fish can swim off at depth after its gas bladder recompresses. Descending a fish back to depth is easier and much less hazardous to both parties than attempting to deflate an over-extended gas bladder with a sharp needle.

It often seems futile to release a rockfish brought up with bulging eyes and a protruding stomach from an over-inflated gas bladder. However, research has shown that more than 80 percent of rockfish survived when returned to depths of 200 to 350 feet if they were returned promptly within 2 minutes of capture. The longer this time the higher mortality is seen. Since mortality rates have been shown to increase the longer that rockfish remain at the surface, it is important to send these fish back down as soon as possible.

On the many WDFW rockfish tagging trips I have helped on out of Westport WA, these fish were landed, placed in a live well, and then measured, sexed, injected with an CWT inset, then released. The total out of water time may have been less than 1 minute. The mortalities were minimal (less than 2%) on fish caught at 50′ or above. The mortality went up considerably the deeper the water the fish were caught at. My estimate would be 15% for those pulled from 100′ of water.

Post Release Mortality : “This has been linked to a number of factors (i.e., fight time, handling methods, water temperature, hook type); however, it is apparent that hook location is among the most critical affecting survival.

According to published results of a Sea Grant study led by researchers at Cal State Long Beach: The degree of barotrauma in a fish is not a reliable predictor of its survival. The most significant predictor of post-release survivorship is the time a fish spends at the surface. In experiments with several species of common southern California rockfish, 83 percent of fish caught at depths between 217 feet and 350 feet, survived when returned to depth within 2 minutes. The odds of a fish dying following recompression nearly doubled with every 10-minute increase in time at the surface.

Tagging and recapture studies showed some released fish were still alive 1.5 years later.

A California study investigating survivorship of juvenile white seabass revealed an overall post-release mortality rate of 10 percent and found that all observed mortalities were associated with hook damage to the visceral (gut) region. Gut hooking not only tears visceral tissue during the fight, but it can also cause osmoregulatory imbalance following the intrusion of seawater into the gut cavity. Additional tearing to the esophagus may also occur when deeply embedded hooks are removed by the angler; therefore, it is highly recommended that the angler simply cut the line close to the hook rather than attempt to remove it with pliers. In juvenile white seabass, survivorship was increased when deeply embedded hooks were left in place (60 percent survival) rather than being removed from the visceral tissue (35 percent survival). For this reason, if you cannot see the hook directly in the lip of the fish, it is good practice to simply cut the line as close to the mouth as possible, preferably while the fish is still in the water.” With that in mind, if you are planning to release your catch, it is good practice to use hooks that are made from metals that corrode quickly, such as bronzed bait hooks.

Venting the Fish : The following was taken out of Saltwater Angler (I think) Feb 2005, which was the product of much experimentation before perfecting this method.

Reef species with spiny rays have closed swim bladders that help produce sound and maintain buoyancy, plus they hold nitrogen, oxygen, and carbon dioxide. When these fish are reeled rapidly to the surface, the gas molecules expand and rupture the bladder. The escaping gasses then fill the body cavity, forcing the eyes to bulge, the intestines to pop out the fish’s anus and the stomach to protrude from the mouth. If the gasses aren’t released (or vented), the fish can’t submerge, which makes it an easy target for predators.

(1) Based on extensive studies by Florida’s Mote Marine Laboratory and other scientific groups, reef fish caught in water depths from 70 to 200 feet have excellent survival rates if the swim bladder gases are vented. To vent properly, follow these steps.


The venting area is in the middle of the trailing edge of the pectorial Fin.



STEP #1; Use a small hollow device like a hypodermic syringe or sharpened basketball inflation needle for a venting tool. Stainless steel is hygienic and resists rust.

STEP #2; With wet hands or a towel, lay the fish flat on top of a cooler or the boat’s covering boards. Gently push the pectoral fin flat alongside the fish’s body.

STEP #3; The venting area is in the middle of the trailing edge of the fin, in the fatty muscle tissue. Using a slight forward angle, slip the venting tool point under the scales and with moderate pressure, push the point barely inside the body cavity.

STEP #4; You will see the belly deflate and hear the gasses escape after the tool is inside. Take care not to puncture the stomach or intestines if they are protruding. Once the pressure is released, the fish will retract them.

NOTE; Don’t use a solid object like an ice pick to vent. The gases won’t fully escape and bacteria may be introduced. Rinse the venting tool after use to clean it so that it is ready for the next fish.

This above article written by Dave Lear, Rich Barrett; Illustration: Chris Armstrong

(1) Team Marine Venting Tool ; Below is a fairly new venting tool used as described above.. CLICK HERE for their website.


Team Marine fish venting tool


With the coastal deep water season, (halibut especially) in the Washington and Oregon waters using limitations on water depth, mortality quotas for Yelloweye and Canary Rockfish, there needs to be a step in the right direction, which ever that is, but geared toward a high rate of incidental caught fish survival. However the WDFW does not condone the above method & prefer that you lower these fish to where the pressure will allow them to swim off on their own.

(2) Sheldon Fish Descender ; That brings us to another product called the Sheldon Fish Descender. The method here is to descend the fish back down to a depth where the water pressure is neared to where the fish was brought up from, allowing the inflated organs to decompress. This can be accomplished by using one of the products designed by Bill Sheldon & sold under the name Sheldon Fish Descender, described on this website

Using the SFD™ as shown below, lower the fish between a minimum of 33 feet and the bottom before releasing. At just over 30 feet the pressure will change by one atmosphere and will assist in recompressing the fish’s air bladder. This device keeps the fish’s mouth slightly ajar and during the decent allows water to move across the gills to remove oxygen and pass CO2 to aid in quick recovery.

The design is simple and has a S shape hook loop that hooks through the fish’s lower lip and holds the fish securely until the line is pulled by a weight which turns the fish upwards and allows the SFD™ to pop out by the fisherman jerking the rod. It jolts and shocks the fish at the time of the release and surges it forward when releasing to help the fish get safely on its way. It also allows a positive finger controlled descent to counter the action of the up and down swells as they move the boat up and down. When the fish has revived, it will signal you by tugging on the line when it’s ready to be released because it has sufficiently recovered or it senses danger from an approaching predator fish or a jellyfish.


Sheldon Fish Descender
Inset the SFD™  into rockfish’s lower lip through the thin membrane near a heavy part of the lip,
with the straight section of the unit outward
Here a separate rod it set up to descend these fish, however you could use just a separate dedicated reel


(3) Milk Jug Crate ; There is another method, but it is more cumbersome by the fact that you need a metal or plastic 4 gallon milk jug weighted crate & a 50′ small rope, invert the box & place it over the floating fish, lower the crate & the fish back down below 30′ & the fish will acclimate itself, & swim off.


Another link that may prove interesting CLICK HERE

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