96 Sharks: The Animal Answer Guide
followed by the North and South Atlantic (92) and the North and South
Pacific (26). Another hotspot of 40 cold temperate sharks is found around
the southern tip of South America, but true sharks are absent farther south
around Antarctica.
The diversity of the major taxonomic groups varies by geographic re-
gion. The greater overall shark diversity in warm temperate regions is in
part due to the large number of squaliform dogfish shark species there (200
species); squaliform sharks are also abundant in the tropics (143 species)
and in cold temperate waters (100 species) but not in the Arctic (5 species).
Scyliorhinid catsharks are likewise (slightly) more diverse in warm temper-
ate than tropical oceans (97 versus 83 species), falling off in cold temperate
waters with only 33 species, and no polar species. Carcharhinid requiem
sharks, in contrast, are most diverse in the tropics (184 species) and the
warm temperate regions (169 species), with a remaining 48 cold temperate
carcharinids. Orectolobiform carpet, bamboo, and Nurse Sharks are an-
other “majority tropical” group, with 44 tropical species, 33 warm temper-
ate species, and 10 cold temperate representatives.
Comparing distribution by depths, squaliforms are most diverse in the
deep sea, carcharhinids are coastal and oceanic, scyliorhinids are coastal
and deep sea, and orectolobiforms are sharks of coastal shallows.
The batoids (electric rays, sawfishes, guitarfishes, skates, and stingrays)
are primarily tropical and warm temperate elasmobranchs that live on the
bottom in relatively shallow water—though with many exceptions. Tor-
pediniform electric rays occur worldwide in shallow warm temperate and
tropical oceans, with a few found as deep as 1,100 m (3,630 ft). Pristid
sawfishes are nearshore, shallow warm temperate and tropical fishes, some
of which enter fresh water. Rhinobatid guitarfishes are also worldwide in
primarily shallow warm temperate and tropical bottom regions. The rajid
skates have a much wider geographic and depth distribution, ranging from
the poles to the equator and as deep as 3,000 m (9,900 ft). As a group, they
tend to live in deeper, cooler water and at higher latitudes than the other
batoids, including a species that occurs in Antarctica and nowhere else. The
myliobatiform rays are again found worldwide in tropical to warm temper-
ate seas, primarily in shallow water, with a number of tropical freshwater
dasyatoid stingrays such as the potamotrygonid freshwater rays of South
America. Overall, the batoids are most diverse in the Indo-West Pacific
region. North and South America are second in batoid diversity.
The holocephalan chimaeras inhabit all but polar seas. Most are deep-
water dwellers at 500 m (1,640 ft) and deeper. One family, the Callorhyn-
chidae, occurs only in the Southern Hemisphere (South America, South
Africa, and Australia / New Zealand). Members of the other two families
(Rhinochimaeridae and Chimaeridae) are found in all the world’s oceans.
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