Geoscience Reference
In-Depth Information
Harvesting of marine resources has systematically exploited the ecosystem, from top predators to primary producers,
such as rockweed.
The changes wrought have been both quantitative and qualitative. Today's groundfish catches are a frac-
tion—3 to 37 percent—of what they were one hundred years ago. Not only did dragging the seabed with otter
trawls scoop up more fish than traditional hook-and-line methods, but the heavy gear also destroyed seabed
habitat. Scientific surveys now show that the numbers of desirable groundfish, such as cod, pollack, and had-
dock, have remained low for the last thirty years, while the numbers of noncommercial species, such as spiny
dogfish, longhorn sculpin, and thorny skate, have steadily increased. After the collapse of the groundfish, their
prey species—shrimps, crabs, lobster, and sea urchins—also burgeoned, signaling a shift in the structure of the
marine food web.
Anadromous fishes fared even more poorly because of the damming of their rivers of birth, such as the St.
Croix, and the indirect, “side-in” effect of pollution. Salmon had nearly been extirpated from the system by
1909. Although effective fishways enabled salmon to return to the river in the 1980s, these populations, along
with all of those from rivers in the inner Bay of Fundy, have since collapsed, perhaps because of high mortality
in the sea from unknown causes. Today, the return of alewives to the river, estimated at a potential 31.7 million
fish, is less than 1 percent of that total. Nutrient enrichment, leading to oxygen depletion, has occurred here, as
elsewhere along the eastern seaboard, notably in Chesapeake Bay, with a decline of long-lived rockweeds and
the more frequent appearance of toxic phytoplankton—“red tides”—killing fish and contaminating shellfish
beds.
