When zoologist Achille Valenciennes first described tarpon in 1847, he noticed their large eyes, which ended up being the inspiration behind his choosing the scientific name of Megalops atlanticus, with Megalops meaning “large eye.” During daylight hours, this feature helps them see fine details, and at night, it increases their visual sensitivity, making them effective feeders 24/7. These large eyes also have a layer of cells that act much like a strip of reflective tape at the back of the eye.
This reflective tape, so to speak, maximizes the capture of light and has a high density of light-detecting rod cells, which give tarpon an advantage when feeding in turbid water or other lower-light conditions. This also explains why anglers often find tarpon hanging around shadows under mangroves and bridges. Essentially, in low-light conditions, tarpon can see the prey better than the prey can see them.
Research on the distribution of vision cells around a tarpon’s eye revealed their eyesight is keenest in upward and forward-looking regions. Combine this fact with the tarpon’s upward-turned mouth, and you realize the best placement for a fly is above and in front of a tarpon’s body.
The cone cells that determine what colors they see are another matter. First of all, fish eyes are very different from ours. Fish retinas contain stem cells that allow the density, distribution and function of vision cells to fluctuate throughout their life, whereas our eyes are static. This allows their eyes to change as the fish move into different habitats and potentially opt for different food sources. And this explains why some flies work for juveniles but not adults. As an example, the colors that juvenile tarpon see are different from those seen by adult specimens. Younger tarpon primarily pick up dark blue and a wide range of green colors. This is because they inhabit turbid waters with greater availability of longer wavelengths of light, like the green colors. When tarpon become adults, their ability to see this range decreases, and their vision in the shorter wavelengths, such as purples and blues, increases. They also develop cells to detect ultraviolet light. This is because when tarpon become adults, they spend more time in clear water, where shorter-wavelength and UV light are more abundant. It is unknown why tarpon see UV light, but there are a couple of possibilities. One is since some fish reflect UV light for communication, tarpon may use the ability to detect prey. Another is, with UV light so abundant in the shallow waters they inhabit, they may use this light to create a background, allowing them to detect the silhouettes of prey that would otherwise be camouflaged. This could explain why a 200-pound tarpon will hit a 3-inch fly.
Tarpon have no vision in the longer wavelengths of the color red, as red light is quickly absorbed in the marine environment. Red flies probably just look black to them in the water.
Tagging projects have revealed remarkable tarpon migrations. Data collected from these efforts have shown tarpon moving over 2,000 miles and sometimes traveling as many as 20 miles in a day. In spring and early summer, they aggregate to prepare for or partake in spawning activities. May, June and July are the spawning months for tarpon in Florida, and satellite tagging has discovered tarpon during this time making brief trips to the Gulf Stream and diving to depths greater than 400 feet. We still don’t know why they make these dives, but they are believed to be related to spawning activity. After spawning, tarpon display a snowbird-type behavior by moving north during late summer and then back south when the coastal ocean waters cool in the fall. These movements correlate with temperature, with tarpon staying in 79-degree-Fahrenheit waters as they move north and south. Their overwintering locations are still a mystery because only a handful of locations have consistently held tarpon in the winter. It’s still unknown where the mother lode of tarpon reside during the winter. Recent research has found them greater than 20 miles from land in the Gulf of Mexico. There are even recent reports of tarpon overwintering on Louisiana oil rigs.
A tarpon’s gut is connected to its swim bladder, allowing the fish to swallow air from the surface. Once the air reaches the swim bladder, oxygen is removed by lung-like tissue called alveolar. This unique air-breathing swim bladder gives tarpon the advantage of obtaining oxygen not only from the water but also from the air above it. Tarpon can actually switch between the two methods as conditions require. For example, the primary organ for obtaining oxygen in water with normal oxygen levels is the gills; however, in water with low oxygen levels, the primary breathing organ is the swim bladder. This explains why sunrise is an excellent time to fish for rolling tarpon. At this time, oxygen levels are lowest because photosynthesis (a chemical reaction requiring light to produce carbohydrates and oxygen) stops during the night. This forces tarpon to roll more frequently to meet their oxygen demand.
One of the advantages of tarpon’s air-breathing behavior is rapid recovery of oxygen debt, as the oxygen level in air is higher than it is in water. This explains why tarpon roll at the surface during an extended fight. Their air-breathing ability, combined with their extensive gill surface area, also reveals exactly how tarpon are capable of these long fights.
Water temperature plays a part in the frequency of tarpon rolling too. In water at or above 79 degrees, a tarpon will roll more often to adjust for its elevated metabolism and the lower oxygen concentration. You can use this information to determine tarpon abundance. If you are fishing in waters 79 degrees or higher and don’t see any tarpon rolling, it’s a safe assumption that they are not in the area. Move on.