Geoscience Reference
In-Depth Information
tions. Along the Northeast shelf, the thermal habitat between 5° and 15°C (40° to 60°F) has decreased in the
last twenty years, while at the same time the coldest and warmest habitats have been increasing. These trends
have produced a habitat “squeeze” for most of the species in the North Atlantic.
Warming seas are driving them to colder waters. Over the last forty years about half of the fish stocks stud-
ied in the Northwest Atlantic have shifted their center of biomass (where they are most abundant) northward or
have moved to deeper depths. As an example of the latter, the distribution of Atlantic surf clams has shifted to
deeper, cooler water in response to increased coastal temperatures. Red hake has moved its central range north-
ward as waters have heated up, and so its numbers have decreased in the Mid-Atlantic Bight and are now con-
centrated in the western Gulf of Maine. The restricted shape of the Gulf of Maine limits the north-south move-
ment of species, and as a result, half of the thirty-six fish stocks examined have also moved to deeper waters to
avoid the warming water temperatures.
A traditional swordfish boat pursues its prey at the surface, while deep-sea species such as ocean perch, or redfish, are
trawled from the sea bottom.
Warming sea surface temperatures are thought to be the cause of a decrease in groundfish and an accompa-
nying increase in pelagic fishes and benthic invertebrates in Narragansett Bay in southern New England. Sim-
ilarly, they have had a dramatic negative effect on sea grass habitat in coastal New Hampshire. Loss of sea
grasses has also been attributed to changes in the timing of bird migrations and storm patterns related to global
warming.
The Gulf Stream is pushing farther north into the Gulf of Maine. Overall, the changes in the fish and inver-
tebrate communities in the Gulf of Maine make it look more like southern ecoregions did in the past. All along
the Northeast U.S. coast, warm-water species are now more dominant than cold-water species. Although
warmer waters boost the growth of adult cod, they will negatively affect survival of cod in early life stages,
and therefore the cod population is expected to decline.
Climate change can also affect the life cycles and migration patterns of local species far from the coast.
American eel populations are in decline because of the mortality of eel larvae attributed to changing sea tem-
peratures and wind conditions in the Sargasso Sea. Similarly, the failure of juvenile salmon (smolt) to survive
once they leave Maine rivers and begin their ocean migration is thought to be related to climate change factors.
Human communities will also be greatly influenced by climate change. Exploited resources, such as fish,
are the historical basis of many coastal communities, and protected species, such as whales, currently attract
