Just when I thought that the only danger in Bull Creek was drowning (or hypothermia presently), a friend gave me something else to worry about- sharks! Although our stream teams are unlikely to run into them, bull sharks can come up the Mississippi north of St. Louis.
A past story in National Geographic that was new to me describes these salt water creatures that can live in fresh water as well. They have been found in the Ganges, Lake Nicaragua, and 2,500 miles up the Amazon.
A map showing their worldwide range is on Wikipedia. These are not true freshwater sharks but migrate to and from the ocean. These sharks have been tagged in Lake Nicaragua and caught in the ocean and visa versa. Like salmon, they are able to jump up the rapids of the San Juan river which connects the lake with the Caribbean.
They are able to live with a 50% dilution of their normal concentrated salt and mineral blood levels. In fresh water they are said to produce 20 times as much urine as when in salt water. (Catheterizing a shark might be an interesting occupation ready for "Dirty Jobs".)
There is much more to the story in the resources above. Meanwhile, don't worry about them when wading our streams (much).
