Sharks – The adaptable old-timer
“Biologically, the species is the accumulation of the experiments of all its successful individuals since the beginning”H.G. Wells (1866-1946), British author. A Modern Utopia Ch 3, Sct 4 (1905; repr in The Works of H. G. Wells, Vol 9, 1925).
Sharks are cartilaginous fish (i.e., having a skeleton wholly or largely composed of cartilage). They vary greatly in size, behavior, and in the way they reproduce. They are found at all depths in all the oceans of the world except the Antarctic. However, they are most abundant in tropical and subtropical waters. A few species of shark inhabit freshwater lakes and rivers, and some migrate regularly from salt to freshwater.
Sharks are remarkably successful animals, with few parasites or diseases and almost no enemies except other sharks, As predators and scavengers, sharks play a major role in the ecosystems of the world’s oceans.
Paleontologists believe that sharks evolved from some primitive, heavily armored, sluggish placoderm that became extinct about 350 million years ago, at the end of the Devonian era. This is approximately when the first shark-like creatures appeared. Sharks almost identical to those living today evolved about 160 million years ago, during the Jurassic period (same time period as represented in the movie, Jurassic Park). This species has survived unchanged for 160 million years in contrast, we poor Homo sapiens have been around for less than million years.
Well-attuned to most of the water of the world, sharks appear to dominate the depths. Swimmers, water skiers, snorkels, scuba divers, and spear fishermen are invading their habitats in every-increasing numbers. Sharks have responded with predictable reflex reactions: They have attacked. The resulting notoriety has given sharks a bad reputation. The mass media have embellished the image, and now most people react with alarm to the word “shark.” However, the facts don’t support this dread of sharks. Of the 100 or so unprovoked attacks that occur worldwide every year, fewer than 35 are fatal.