The Massachusetts Division of Marine Fisheries (MDMF) has released an article on how anglers can enhance the survival of released fish that have experienced “barotrauma”—which often occurs in fish that have been brought up quickly from deep water. The information contained in this article is taken from the MDMF article.
Barotrauma occurs when a sudden change in depth, coupled with the drastic temperature change between the ocean floor and the surface, causes the air in a fish’s swimbladder to expand at a rapid rate. Depending on the species of fish, the swim bladder may expand to a large size, displacing internal organs. It may also rupture, sending gas into the body cavity, eyes, or muscle tissue.
Neither scenario is good for the health of the fish, especially if the fish is of sublegal size or is not a desired species for the angler to retain. When released, the barotrauma-inflicted fish is not able to swim downward and is left to float on the surface of the water.
So-called “venting tools,” which are large needles that can be inserted into the abdominal wall of the fish to release the internal gas, can be effective in some cases; however, they can also injure internal organs and potentially introduce infection.
A better alternative is a “release device” that transports the fish to the depth at which it was hooked. Most of the devices currently on the market attach to the fish’s mouth and can be used on a fishing rod. When the fish reaches the bottom, the device releases the fish. One such device is pressure-sensitive, and releases the fish once the desired depth is reached. Another uses a reverse, barbless hook that requires a slight tug on the line to allow the fish to slide off. Another type of release device can be made at home using nothing more than a milk crate, heavy weights and piece of rope. The milk crate is inverted on top of the fish and lowered by hand to the desired depth before being pulled up, leaving the fish behind. Pretty simple!