Have you Heard About the Nicaragua Fresh Water Sharks?
As a kid, my dad used to tell me the story about the fresh water sharks that lived in Nicaragua, and how these where the only fresh water sharks in the world! This was almost 50 years ago, and mankind did not really know much about marine life, sharks included. Thanks to the interest spawned by Jacques Cousteau, that marine scientist that we all loved to watch on the TV as kids, we have learned and understood a lot about marine life and sharks in particular. So, is the myth about Nicaragua fresh water sharks true or not you will ask?
Well… it sort of is true! Yes sharks to do swim in the waters of Lake Nicaragua, and although their numbers have dwindled over the years, there is plenty of scientific evidence that they in fact live and thrive in this huge freshwater lake. However, it turns out that the Nicaragua fresh water sharks are not actually a different species of sharks, but rather good old bull sharks that swim up the mighty San Juan River and end up in Lake Nicaragua!
Modern studies have found that sharks and other salt water fishes and mammals actually do swim up rivers. They do so in search for calmer conditions and less competition for food. Bull sharks have been reported in the Orinoco and Amazon Rivers in South America. The same can be said for the Papaloapan River in Mexico. But why do you not find these sharks in rivers such as the Mississippi in the USA or the rivers in Europe? Well, the answer is easy, sharks thrive in the warm waters of the Caribbean. They require similar temperature in the rivers, the tropical rivers of Mexico, Central America and South America offer ideal conditions. The rivers further north offer water that is usually the result of snow melt and is therefore downright cold!
The reason that these sharks are found only in Lake Nicaragua is actually quite simple. The San Juan River connects the lake to the Caribbean Sea. The river traverses about 220 km from the outlet in Lake Nicaragua, which is only 30 meters above sea level, to the delta in the Caribbean. The current is slow and offers a steady flow of water. This means that sharks can actually navigate these 200 plus kilometers up the river into the lake! Over the years, the San Juan River delta has become clogged with sediment. This has made the passage between the Caribbean and the River rather hazardous for the sharks to navigate in. This, together with over fishing, has generated a sharp decline in the number of Nicaragua fresh water sharks.