186 Sharks: The Animal Answer Guide
to be the chief cause of decline in all these examples because it interacts
with aspects of the basic biology of shark species that make them vulner-
able to exploitation.
Because many sharks mature slowly and produce relatively few young
at long intervals, they are easily overfished and their populations are slow
to recover, if at all. Add to this the tendency of individuals to cross entire
oceans, during which time they are exposed to fishing in multiple countries
and on the high seas. Protective measures in one country do little to pro-
tect sharks when they travel to another region where protection is nonexis-
tent. And the open ocean is largely unregulated and even harder to patrol.
Given these biological traits and circumstances, it is not surprising that
commercial shark fishing has a long history of collapse. A typical shark
fishery experiences initially high catches of a previously unexploited stock,
followed by reduced landings despite increased effort, and eventual decline
in catches to the point that it is no longer economically profitable to keep
fishing. After most fishing ceases, populations are slow to recover, if they
recover at all. Examples of sharks that have been overfished include Com-
mon Thresher Sharks and Pacific Angel Sharks in California; Angelsharks
(Squatina squatina) in the Irish Sea; School Sharks and 12 species of deep-
water squaliform dogsharks including Portuguese Dogfish off Austra-
lia; Spiny Dogfish in the North Atlantic; Basking Sharks off Ireland and
British Columbia; Bull Sharks and Largetooth Sawfish (Pristis microdon) in
Lake Nicaragua; Soupfin Sharks (Galeorhinus zyopterus) off the U.S. Pa-
cific coast; Brazilian Guitarfish (Rhinobatos horkelli) in the southwest Atlan-
tic; and Porbeagle Sharks off Newfoundland. Even chimaeras are subject
to overfishing because, like sharks, they have a slow reproductive cycle. A
fishery in New Zealand for Australian Elephant Fish collapsed in the 1980s
from overfishing and has taken two decades to show signs of recovery.
The Porbeagle fishery of the western North Atlantic provides a classic
example, collapsing after only six years. Exploitation began in 1961, with
landings averaging 4,500 metric tons (MT; 9.9 million lb) per year prior to
the collapse, when catches fell to around 350 MT (772,000 lb), or 8% of
initial landings. Relaxed fishing led to partial recovery of this species, but
only to about 10% to 20% of the original levels. Soupfin Shark landings off
California peaked at 4,000 MT (8.8 million lb) in 1939, fell to 2,300 MT
(5.1 million lb) in 1941, and five years later were down to 270 MT (595,000
lb), or 7% of the peak, despite intensive effort. Thirty years afterwards,
populations were still below the pre-exploitation levels of the 1930s.
The history of the Basking Shark “fishery” off British Columbia is par-
ticularly sad because it involved the deliberate extirpation of a harmless
giant species of no commercial value, eliminated solely because it was con-
sidered a nuisance to fishing interests. As slow-moving, plankton-feeding
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