188 Sharks: The Animal Answer Guide
Atlantic indicate that between 1985 and 2000, hammerheads were reduced
89%; thresher sharks, 80%; White Sharks, 79% (more than 6,000 cap-
tured); Oceanic Whitetips, 70%; Tiger Sharks, 65%; Blue Sharks, 60%;
and several other species, 49% to 83%. Estimates from the Mediterranean
put the declines of hammerheads, Blue Sharks, Porbeagles, Shortfin Ma-
kos, and thresher sharks at 96% to 99% of their former abundance. Reduc-
tions of this order at a global level would qualify these species for endan-
gered or critically endangered status according to the IUCN criteria. The
magnitudes of those estimates have been hotly debated in the scientific
community, but biologists uniformly agree that the pattern of population
reduction is globally widespread and of great concern.
Given these apparent historical patterns, fisheries for certain elasmo-
branch species have been increasingly regulated (some say too little too
late), although many countries still lack any curbs on shark fishing. Inter-
national protection has increased for Whale Sharks, Basking Sharks, and
White Sharks, all three of which are protected from international trade by
the Convention on International Trade in Endangered Species (CITES).
In March 2013, six more species were given CITES protection: Oce-
anic Whitetip, Porbeagle, Scalloped Hammerhead, Great Hammerhead,
Smooth Hammerhead, and both manta rays. The mantas, which are exceed-
ingly slow breeders, have come under intense recent fishing pressure for
their gill plates (see “Are any medicines made from sharks?” in chapter 8).
Whale Sharks are vulnerable because they do not occur in separate pop-
ulations but instead make up one large global population. The entire world
population of breeding-age Whale Sharks has been estimated at between
only 27,000 and 180,000 individuals. Whale Sharks may be additionally
vulnerable to exploitation because females tend to aggregate periodically in
just two regions, the southern end of the Gulf of California in Mexico and
the Galapagos Islands off the coast of Ecuador. This means that a significant
number of females could be removed from the world population if fishing
were allowed at those locales. Fortunately, the Galapagos Islands are one
large marine refuge, and it is illegal to catch Whale Sharks in Mexico (al-
though enforcement in both locations is hampered by a lack of funds).
Some species are exposed to extreme fishing mortality even though they
aren’t targeted by a fishery. Their size and anatomy cause them to be caught
incidentally, a phenomenon known as bycatch. The giant Barndoor Skate
of the northwest Atlantic and its relative the Blue Skate of the northeast
Atlantic, ironically known also as the Common Skate, are caught in trawl
nets dragged along the bottom that target shrimp, cod, or flatfish. The
openings in the nets (mesh size) allow juveniles of most fishes to escape,
but these rays are born at a size too big to slip through the nets. Both skates
declined drastically in numbers and were thought to be threatened with
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