Environmental Engineering Reference
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accelerating, and that by 2003, the stocks of 29% of all currently i shed species
had to be considered collapsed. Moreover, that study also found that despite sub-
stantial increases in i shing effort, cumulative yields across all species and large
marine ecosystems had declined by about 13% after reaching a maximum in 1994.
Not surprisingly, these declines have affected most of all the largest predators, tuna,
billi sh, and swordi sh.
Using the logbook data from Japan's worldwide i shing activities, Worm et al.
(2005) demonstrated that between 1950 and 2000, the predator species density
showed gradual declines of about 50% in both the Atlantic and Indian Oceans and
about 25% in the Pacii c. And Pauly (2009) concluded that commercial i shing
has reduced the zoomass of traditionally harvested large demersal and pelagic
species (cod, tuna) by at least an order of magnitude. Despite our surprisingly poor
understanding of actual i sh stocks and their dynamics, there is no doubt that most
of the traditionally targeted species and most of the major i shing areas now belong
to three unwelcome categories: those whose the stocks have already collapsed or
are close to doing so, those that continue to be overi shed, and those that are i shed
to their full capacity.
The declines have affected many species that have been traditional food choices
for millennia and whose catches switched from abundance to scarcity or even to
total collapse within often very short periods of time. The already noted collapse
of the Canadian cod i shery and the sharp declines in bluei n tuna have attracted a
great deal of attention: Mediterranean and Atlantic populations are particularly
endangered, and even the larger Pacii c tuna population may crash at any time. But
there are many less reported declines, including the low counts of one of Western
Europe's well-liked species: the numbers of European eels ( Anguilla anguilla ) have
declined sharply since the 1970s, perhaps by as much as 99%, while the effective-
ness of restocking efforts remains uncertain (Vogel 2010).
The third notable change that is not captured by the seafood-NPP appropriation
ratio has been a gradual decline in landings of larger, slow-growing, and more valu-
able carnivorous top predator species (tuna, cod, halibut) and the rising harvests
of larger amounts of smaller, faster-growing, less valuable species that either are
herbivorous (primary consumers) or feed largely on zooplankton (Pacii c anchoveta
and herring). Pauly et al. (1998) traced these specii c changes during the latter half
of the twentieth century and discovered that the mean trophic level of reported
landings declined from slightly more than 3.3 during the early 1950s to less than
3.1 in 1994, with the index as low as 2.9 in the northwestern and west-central
Atlantic.
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