Sharks in lakes? Now that sounds absurd…. Doesn’t it? Well apparently not. On the border of Costa Rica and Nicaragua lies the enormous Lake Nicaragua. The largest lake in Central America, Nicaragua is bound to hold plenty of secrets, and due to its lack of salt and sheer size (8000 sq kilometres) it certainly does. Bull sharks are seen around the coast of Costa Rica, especially at the bat islands and further afield. In centuries past, the lake and the ocean created a giant bay, and as the lake dried and the land masses moved together ever so slowly the sharks were trapped in the landlocked lake. As we know sharks are prehistoric creatures and therefore this phenomenon could have taken place millions of years ago. As the lake turned from salt to fresh water the sharks started to adapt to their new surroundings.
Scientists in 1961 made startling discovered that these Lake Nicaraguan sharks are beginning to act like salmon. The sharks have learned to travel up the San Juan river by jumping upstream as far as 120 miles all the way to the Caribbean Sea. Its seems strange, especially as the Pacific is only 12 miles away at the closest point however there are no rivers to the west. Once thought an endemic species to the lake, it has now been confirmed that they are indeed bull sharks, a species known to reside in rivers in Africa and even golf ponds in Florida and Australia. Bull sharks are known for their aggressive nature and willingness to eat almost anything. One bull shark was found with a car licence plate in its stomach.
Healthy bull sharks can reach a size of 11 feet and 500 pounds. Fast, agile predators, bull sharks often feed on fish, dolphins and even other sharks.
It is thought that the sharks spend their infancy in the lake before making the risky migration to the sea. If the water level is low and there is a large silt build up in the San Juan river the sharks will almost definitely die. While this is a miraculous journey and discovery, bull sharks in the Amazon have been recorded to swim as far as 2,600 miles up the colossal river.
While there have been 3 recorded shark attacks in Lake Nicaragua, there is minimal risk to humans, in fact it seems that sadly the lakes shark population is declining due to habitat destruction and the lack of seasonal rains.