Human Problems (from a shark’s viewpoint) 187
surface dwellers, Basking Sharks frequently became entangled in nets set
or towed to catch other species such as salmon. Removing a 10-m-long
(33-ft) animal from a net was inconvenient to fishermen, prompting a tar-
geted campaign to rid the ocean of the inconvenience. Basking Sharks
caught in nets were butchered and discarded, harpooned and discarded,
shot for sport, and rammed and discarded by government boats specially
equipped with knife-edged can openers on their bows. Records indicate
that hundreds if not thousands of Basking Sharks were killed between 1920
and 1970. Since then, “only a handful of basking sharks have been sighted
or caught... [representing] the first extirpation, in the true sense of the
word, of a marine species” (Dulvy and Forrest, 656–57, in Carrier, Musick,
and Heithaus 2010).
In most of these examples, the species became commercially rather than
ecologically or evolutionary extinct. Commercial extinction occurs when
a species falls to such low numbers that the effort that goes into catch-
ing the species makes it unprofitable to pursue, meaning that costs exceed
profits. Commercial extinction precedes ecological extinction, which de-
scribes population levels so low that the species no longer functions in its
natural role within an ecosystem. Commercial and ecological extinction
are steps along the path to evolutionary extinction, or the death of the spe-
cies. Springer and Gold (1989, p. 14) predicted this course for sharks when
they wrote, “It seems certain that some species of sharks will be depleted
and, perhaps, extinguished by man’s activities.”
In the ensuing two decades, their prediction has proven disturbingly
correct. Shark and ray populations have crashed in many locales, and many
species have been placed on endangered species lists, necessitating their
protection from further exploitation. Some estimates from the North
A campaign button to promote
conservation of Spiny Dogfish, pro-
duced by the Ocean Conservancy.
An international effort was mounted
to reduce allowable catch rates to
preserve Spiny Dogfish stocks, es-
pecially in the Atlantic Ocean. New
catch limits were established in
2000 for the Maine to Florida fish-
ery. Once catch quotas are reached,
fishing is supposed to cease. Photo by
Gene Helfman