Why Tarpon Roll
You know the sound. You know the feeling. You’re standing on the bow of a 17 Yellowfin Skiff in Key West Harbor on a May morning before the sun rises. It’s dark and the wind is calm. You listen intently.
You hear a sound like an air bubble popping on the surface of the water, something like a gulp of sorts. You can’t exactly tell where the sound came from, somewhere to your right, but you know that it’s out of casting range. You hear more gulps and some splashes.
Before long, the school starts to roll closer to your boat, seeming to turn in random directions before you can cast. Either they are moving a lot, or there are a lot of them. The sun starts to rise and you can see them now. Silver heads and backs taking gulps of air around you. You start to false cast and land your fly 10 feet in front of a silver head that recently disappeared.
You begin to strip the fly and the line jerks and tries to jump out of your fingers. With an eruption of whitewater, the tarpon breaks the surface to shake its head and stretch its gills. As quickly as it started, it’s over. The fly line is slack now and you strip the fly back in to start another cast with shaking fingers. At 8am, the show is over and the tarpon disappear into the green and blue water of the harbor.
The tarpon roll is an iconic display of the mysterious fish. While it can tremendously help in locating the fish, there seems to be only key times, locations, and days where “it’s on”, and the tarpon roll the way you have always wanted them to.
Before we dive into the reasons why tarpon roll, it’s important to understand how a tarpon can breathe oxygen and certain aspects of their anatomy.
What Allows Tarpon to Roll?
If you’ve ever filleted a fish, you’ve probably come across a swim bladder. The swim bladder of other bony fish looks like a balloon that you can pop and is used by the fish to help maintain neutral buoyancy, so they don’t sink to the bottom or float to the surface.
While the tarpon will breathe primarily through their gills, they also breathe oxygen. When tarpon take a gulp of air, or roll, the air goes to their swim bladder. A Tarpon’s swim bladder is lined with lung-like material that can filter oxygen out of the air. The oxygen is then distributed to the rest of their body with special arteries that are connected to the swim bladder.
According to Dr. Mike Larkin, there are three key factors that explain why tarpon roll: low oxygen levels, to adjust buoyancy, and imitation. Let’s examine each one of these in depth.
Low Oxygen Levels
If you’ve ever taken a chemistry class, you may remember that the air contains about 21% oxygen. What you may not remember is that water contains only about 1% oxygen, depending on temperature. The higher the temperature of the water, the lower the oxygen content is.
When the oxygen levels in the water are low, tarpon will roll more to take advantage of the higher oxygen content in the air. One particularly important example to the tarpon lifecycle is that when tarpon are young, they seek out oxygen-poor, stagnant creeks to avoid predators. Rolling and consuming oxygen from the air will allow tarpon to flee from predators and establish safe zones that other fish and predators cannot access.
The dedicated tarpon fisherman may notice that tarpon roll more at night and in the morning than any other time of day. This is because the sun plays an important role with oxygen levels in the water. Photosynthesis, the process of plants producing oxygen and glucose from carbon dioxide and sunlight, allows more oxygen to stay dissolved in the water during the day. At night, aquatic plants and algae will solely rely on cellular respiration, which is the process of converting oxygen and glucose into water and carbon dioxide. Essentially, there is less oxygen dissolved in the water during the night, which encourages tarpon to rely more on the oxygen in the air than in the water.
Wind speed also raises some interesting findings. When wind speed is high, the water will be churned up more. This gives oxygen more of a chance to dissolve into the water, similar to the workings of a riffle on a trout stream. Generally, the higher the wind speed, the more oxygen saturated the water will be, and the less the tarpon will roll. On clear, slick calm days, the water will not be as oxygenated. This will encourage tarpon to roll more.
The level of exertion a tarpon is faced with also affects how much a tarpon will roll. Like when we workout and start breathing harder due to lower oxygen levels in the bloodstream, tarpon have a very similar response. This can manifest itself when a fisherman is fighting a tarpon, when a tarpon is feeding, or when a tarpon has to swim against current. The advantage of taking gulps of oxygen while fighting a fisherman is greatly increased endurance. This is one of the main reasons that you can fight a tarpon for an hour and a half.
Adjusting Buoyancy
The main purpose of a swim bladder in other bony fish is to maintain neutral buoyancy. Because tarpon “breathe” through the lung-like lining on their swim bladder, they need to regulate their buoyancy throughout the day and night.
In order to get the proper amount of air into their swim bladder to be neutrally buoyant, tarpon will take a big gulp of air on a roll, then slowly let it out until they can feel that they no longer sink or rise in the water column. They do this by releasing a bread crumb trail of bubbles after they roll. Tarpon fisherman may notice this as a good opportunity to locate the direction of the fish after they roll.
Imitation
Interestingly enough, scientists have discovered that tarpon will roll purely out of imitation of one another. To measure and prove this, scientists placed tarpon in side-by-side, separate tanks to eliminate the feeling or sound of a tarpon rolling in their lateral lines. The only sense they would have of another tarpon rolling beside them was sight.
When one tarpon rolled, the other tarpon had a 70% chance of rolling right after. Scientists then made a wooden tarpon, painted it, and put it in a tank next to the tarpon. When they raised the wooden tarpon decoy up to the surface to simulate a roll, the tarpon next to the decoy had the same 70% chance of rolling.
Scientists even tested imitation rolling with a plain kitchen spatula, raising it to the surface to simulate a roll, and achieved similar results. If there’s room for another major innovation in tarpon fishing, it could be a decoy.
Key Takeaways
Expect Tarpon to roll the most in the mornings on clear, slick calm days and at night
Tarpon will roll during a fight with a fisherman to greatly increase endurance
Tarpon will roll to adjust buoyancy and will leave a bread crumb trail of bubbles that an angler can follow to estimate the direction the tarpon goes after rolling
Tarpon will roll just to imitate each other
Did you enjoy this article? Listen to Dr. Mike Larkin on the Tom Rowland Podcast for the full interview and watch Saltwater Experience to see some Tarpon action
About The Author
Turner Rowland was born in Key West, Florida and has an avid passion for
Inshore and offshore fishing. After moving to Tennessee early in life, he began a life-long fascination with wildlife, hunting, and fishing that has taken him around the world to places like Bolivia, Christmas Island, Alberta, South Africa, Zimbabwe, and Zambeze. He currently resides in Bozeman, MT where he is passionate about elk, deer, turkey, duck, antelope, and bear hunting after cutting his teeth as a wilderness elk hunting guide.