Shark Ecology 85
to congregate (see “How can I see sharks in the wild?” in chapter 8), it is
likely that some of these are the same sharks, meaning hammerhead popu-
lations are smaller than if we were looking at entirely separate groups.
Even comparatively small coastal sharks can cover large distances dur-
ing their lifetimes, and the distinction between “coastal” and “oceanic” is
far from hard and fast. Some coastal species will cross deep ocean areas to
get to another coast. A School Shark less than 1.5 m (5 ft) long that was
tagged off New Zealand’s South Island was caught 4,940 km (3,069 miles)
away off South Australia, 3.5 years later. To get to Australia, it had to cross
the stormy Tasman Sea, which is more than 5,180 m (17,000 feet) deep.
Spiny Dogfish are most common along coastlines and generally move up
and down a coast, but some fish don’t know this. One tagged off the coast
of Newfoundland crossed the Atlantic Ocean and was captured near the
Shetland Islands 11 years later, a minimum distance of more than 3,200 km
(2,000 miles). Spiny Dogfish tagged off the west coast of Canada moved
long distances along the coast, traveling north in spring and summer and
south in fall and winter. Some were recaptured years later up in Alaska and
south in Washington State, Oregon, California, and Mexico. But several
traveled to Japan, across the North Pacific Ocean.
The champion horizontal migrators are species that cross ocean basins
or move north and south between hemispheres. Blue Sharks make round
trips across the Atlantic between North America and Europe, a straight-
line journey that exceeds 16,000 km (9,900 miles), although the sharks un-
doubtedly cover more area because it’s unlikely they swim in a straight line.
Some Blue Sharks move north and south; a Blue Shark that was tagged
off New York was later recaptured off Brazil, a one-way straight-line jour-
ney of 5,980 km (3,715 miles). Some other long distances traveled by oce-
anic species in the North Atlantic include 6,700 km (Tiger Shark), 4,500
km (mako), and 2,800 km (Oceanic Whitetip)—but again, these distances
A Scalloped Hammerhead at Cocos
Island, off the coast of Costa Rica.
Scalloped Hammerheads migrate
between Cocos Island, the Galapa-
gos Islands, and Malpelo Island off
Colombia, forming large aggrega-
tions. To protect this globally endan-
gered species, fishing in all three
areas needs to be stopped. Photo by
Barry Peters, Wikimedia Commons, http://
en.wikipedia.org/wiki/File:Scalloped_hammer
head_cocos.jpg