Lake Nicaragua is Central America’s largest lake. It’s so large that the first Spaniards to set foot on Nicaraguan soil mistook it for an ocean! But, its size isn’t what makes the 110 mile body of water one of the world’s most fascinating lakes. Rather, it’s what lies below its silvery surface: one of the world’s few freshwater shark species.
Nicaragua’s bull shark is one of the few shark species capable of surviving in fresh water. It can measure up to 11ft and splits its time between the vast fresh waters of Lake Nicaragua and the salty ones of the Caribbean sea- adapting its body’s salinity levels according to its environment.
When living in fresh water, the shark’s blood is saltier than the water around it. In order to survive, it must lower its body’s salinity levels to match the water around it. It does this by by urinating frequently and making use of the special set of filtration glands near its tail.
Bull sharks access Lake Nicaragua via the San Juan River, which connects the lake to the Caribbean sea. Like salmon, bull sharks jump upstream until they reach the lake where they are able to swim in warm, shallow waters and feed on the lake’s fresh water fish. The lake also provides juvenile bull sharks with a place to mature away from predators like other shark species.
Bull sharks are slate grey with a bright white underbelly and pointed dorsal fin that sticks up out of the water when they are about to breach the surface. Although they are often found in shallow waters, very few humans come in contact with the mighty creatures…So paddleboard away! You won’t be running into one of these guys any time soon.