Sturgeon are among the largest fish in North American rivers, and they regularly launch their whole bodies clear of the water. Scientists still haven’t settled why. The best explanations point to two needs that have nothing to do with escaping predators or catching food: managing air inside the body and keeping in touch with other sturgeon.1PubMed. Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour2Journal of Applied Ichthyology. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA On busy rivers a jump is more than a curiosity, because a fish this size can land in or against a boat.
Gulping Air to Control Buoyancy
Like many fish, a sturgeon has a swim bladder, a gas-filled sac that works like an internal float. A sturgeon’s swim bladder connects to its throat, so the fish can refill it by gulping air at the surface. For Atlantic sturgeon, that gulping is the leading explanation for why they come up at all.3PubMed. Atlantic sturgeon Acipenser oxyrinchus surfacing behaviour
The float matters because a swim bladder only keeps a fish neutrally buoyant at one depth. Gas squeezes as the fish goes deeper and expands as it rises. A sturgeon that sinks to deep water loses some of its lift, and has to make up for it by swimming or by adding gas. Most fish adjust their float with gas from their blood, but sturgeon can also use air from above. A sturgeon that has spent a long time deep may need a burst to the top to restore its float. Staying neutrally buoyant lets a large, heavy fish rest near the bottom without burning energy to stay there.
Tracking tags on adult Atlantic sturgeon off Canada’s Bay of Fundy recorded fast climbs from deeper than about 130 feet (40 m) to within 30 feet (10 m) of the surface.4PLoS ONE. Oceanic Distribution, Behaviour, and a Winter Aggregation Area of Adult Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, in the Bay of Fundy, Canada Individual fish made these rapid ascents about 2 to 7 times a month through the winter, up to 8 in a single month.5PLoS ONE. Oceanic Distribution, Behaviour, and a Winter Aggregation Area of Adult Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, in the Bay of Fundy, Canada Such fast rises can carry the fish into a leap out of the water.6PLoS ONE. Oceanic Distribution, Behaviour, and a Winter Aggregation Area of Adult Atlantic Sturgeon, Acipenser oxyrinchus oxyrinchus, in the Bay of Fundy, Canada
A jump might work better than a slow rise for gulping air. A heavy fish rising fast builds momentum that can carry it through the surface, and breaking through in one burst lets it grab air quickly and drop back down. That idea explains a burst to the surface better than it explains a high, showy leap.
It also leaves things unexplained. It doesn’t say why many sturgeon jump in the same stretch at the same hours, or why jumping peaks in certain months. That is why researchers think jumping may do more than one job.
Splashing to Keep the Group Together
On Florida’s Suwannee River, recordings of Gulf sturgeon jumps match each sound to a stage of the leap.7Journal of Applied Ichthyology. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA A jump comes with a loud smack plus a series of underwater snapping sounds before and after, in a repeated, set pattern.8American Currents. Catching Air – Those Magnificent Jumping Suwannee Sturgeons These sounds differ from those of other jumping fish and from objects dropped in the water.9Journal of Applied Ichthyology. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA That fits the idea that jumping is a form of group communication, though other explanations aren’t ruled out.10Journal of Applied Ichthyology. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA Because the sounds come in the same order each time, a listener can recognize a sturgeon jump without seeing it. Murky, tannin-stained water limits how far a fish can see, while sound travels well and far underwater.
Gulf sturgeon gather in summer “holding” areas, sitting in the same river stretches for weeks.11Journal of Applied Ichthyology. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA The jumps may tell others where the group is, like cattle mooing in a field.12American Currents. Catching Air – Those Magnificent Jumping Suwannee Sturgeons Proving it would require showing that other sturgeon actually respond to the sound, which is much harder than recording it. The two ideas can both be true, and neither has been shown to rule out the other.
When and Where Sturgeon Jump Most
On the Suwannee, jumping was far more frequent in June than in April, May, August or September.13Wiley Online Library. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA In mid-summer, before thunderstorm season peaks, the best spots can see 6 to 10 jumps a minute.14American Currents. Catching Air – Those Magnificent Jumping Suwannee Sturgeons Over 1,000 jumps a day were counted along a half-mile stretch.15Wiley Online Library. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA
That intensity comes from where the fish are. Gulf sturgeon concentrate in a limited number of river stretches in summer, so jumping is packed into small areas rather than spread along the whole river. The very high counts come from a short measured stretch, so they describe the busiest spots, not the whole river.
Outside June, jumping peaks near dawn and less strongly near sunset.16Wiley Online Library. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA In June jumps run all day, slowing most at midday.17Wiley Online Library. Why do sturgeons jump? Insights from acoustic investigations of the Gulf sturgeon in the Suwannee River, Florida, USA So in June you don’t have to be on the water at dawn, while in other months dawn is the better bet and evening a weaker second chance.
It isn’t one fish jumping over and over, but hundreds each jumping about once a day.18American Currents. Catching Air – Those Magnificent Jumping Suwannee Sturgeons If you see a jump, don’t expect that same fish to go again right away.
To watch for jumps, go early in the morning in late spring and summer. Stay still and quiet near known holding stretches and listen for a heavy smack. Watch from shore or a well-anchored boat away from the channel, and remember that jumps are unpredictable, so a burst can come right beside you.
Other fish leap in the same rivers, so it helps to know what you’re seeing. Sturgeon have rows of bony plates along the body instead of smooth scales, a long snout, and a tail whose upper lobe is longer than the lower. Gulf sturgeon can be several feet long and very heavy, unlike the mullet that leap often in the same waters.
How Dangerous Are Jumping Sturgeon
One Florida trauma center treated 8 people hurt by leaping sturgeon in about a year and a half.19The American Surgeon™. Sturgeons versus Surgeons: Leaping Fish Injuries at a Level I Trauma Center Injuries included broken bones, torn livers, severe facial injuries and a head injury.20The American Surgeon™. Sturgeons versus Surgeons: Leaping Fish Injuries at a Level I Trauma Center A large fish leaping into a boat strikes with great force. If the boat is also moving, the collision includes the boat’s speed as well as the fish’s weight. The fish is hard-bodied, with bony plates, so a strike is like being hit by a hard object.
Face and head injuries show that people sitting upright in a moving boat can be hit at head height by a fish in mid-leap. Torn livers show that serious damage can happen inside the body.
Sturgeon aren’t attacking. Fish jump without aiming at boats, and the danger comes from crowded fish meeting crowded boats. Gulf sturgeon are protected, so harming or keeping them is illegal.
Awareness and safe boating are key to reducing these injuries.21The American Surgeon™. Sturgeons versus Surgeons: Leaping Fish Injuries at a Level I Trauma Center Slow down on sturgeon rivers, especially in summer and early morning. Wear a life jacket and keep children low in the boat. At low speed you have time to react to a fish in the air.
If someone is struck, check for head, face and chest injuries first. Call for help and head to shore. A hard blow to the belly can hurt the liver even without visible wounds, so seek medical care even if the person seems fine.