for estimating stock size, explicitly because it was the basis of Myers and Worm’s
claims. Long lining has indeed not been a consistent practice, and different stocks are
differentially susceptible to changing depths of the baits and other modifications.
Some stocks, particularly yellowfin tuna in the eastern tropical Pacific, have declined
and then recovered to an extent, and a case can be made that they are sustainably
harvested. However, others, particularly the larger sizes of bluefin tuna (Thunnus
thynnus), prized for sushi, are stocks in extremis. The value of such fish interacts with
availability to sustain fishing, even though catches diminish to nearly zero. One large
bluefin (377 kg) was sold for $396,700 at Tsukiji market in Tokyo in January 2011.
That much money can buy lots of boat fuel and search time. The value has also led to
live harvest of young specimens for pen-rearing off Australia and in the
Mediterranean, which has its own problems and may or may not relieve pressure on
the wild stock. Ten percent may or may not be the best overall generalization for high-
level predatory fish, but the global reductions in only about 50 years surely have
strongly modified ocean ecosystems. Because of the shifting baseline effect, even
ocean biologists come to think of the new situation as normal.
Fig. 17.23 Time-series of CPUE (catch per hundred hooks fished) for different ocean
areas fished by the Japanese long-line tuna industry.
(^) (After Myers & Worm 2003.)