Shark Ecology 93
with Largetooth Sawfish (Pristis microdon), have been heavily overfished in
Lake Nicaragua and are now protected by Nicaraguan law. Bull Sharks oc-
casionally swim up a river and then get stranded in water bodies after a
flood. This is the probable explanation for how several Bull Sharks got into
a water hazard at the Carbrook Golf Club in Brisbane, Australia. It’s pru-
dent to just take a penalty stroke if you find yourself in the lake on the 15th
fairway at Carbrook.
All six (or maybe seven) species of sawfishes inhabit estuaries and rivers.
The Largetooth Sawfish has been found as far up the Amazon as Santarem,
Brazil, more than 800 km (500 miles) from the sea. Largetooth Sawfish es-
tablished a genetically distinct reproducing population in Lake Nicaragua
but have become increasingly rare as a result of overfishing and habitat
destruction. Because of their large size, dangerous tooth-studded snouts,
and tremendous strength, sawfishes are the stuff of legend and respect in
many countries (see “What roles do sharks play in religion, mythology, and
legends?” in chapter 11). Unfortunately, they are also among the most en-
dangered elasmobranch species in the world.
Several sharks and sawfishes move freely between marine and fresh wa-
ter, prompting the question of how they deal with such drastically chang-
ing salinities. Unlike the full-time freshwater species, these estuarine mi-
grants can adjust the molecular concentrations of their blood. A Bull Shark
in fresh water reduces the salt concentration of its blood by about 20% and
the urea concentration by about 50%. It also compensates for the extra
Sawfishes were once common in
tropical nearshore areas around
the world. They are now among
the world’s most imperiled marine
and estuarine fishes. Shown here
are saws taken from sawfish during
a 1920 fishing tournament in Key
West, Florida. Photo property of Matthew
McDavitt; photographer unknown