after R. Jones and H. Larson. 1974. A key to the families of fishes as recorded
from Guam. Univ. Guam Marine Laboratory, Tech. Rep. 10. 48p.
are some of the marine resources in our offshore waters? Three ocean resources
of potential interest to American Samoa are fish, minerals and the water itself.
Several kinds of food and sport fish are present in modest numbers: tuna, masimasi,
marlin, wahoo, sharks, and flying fish. Surveys indicate, however, that the abundance
of oceanic fishes within our 200-mile limit is probably not high enough to warrant
significant commercial development of offshore fisheries. That's the main reason
why the big tuna boats that deliver to American Samoa's canneries travel far beyond
our 200-mile zone to other locations where the tuna are more abundant (the canneries
are located here only to gain duty-free access to US markets).
resource mentioned from time to time are mineral deposits, such as manganese nodules,
that lie on the seafloor. However, these nodules, even if present in our waters,
are too deep for economic extraction by current technologies.
a more exploitable resource in the future involves the temperature of the ocean's
cold bottom layer. Scientists are working on a technology that extracts energy
(to produce electricity) through a heat-exchange mechanism that is made possible
by the large temperature difference between the tropical ocean's warm surface
and cold bottom layers. A demonstration facility for this technology has been
operating in Hawaii since the 1970's, but it has been an uneconomical venture
so far. The two requirements for this technology -- a large temperature differential
in the ocean, and easy access to this temperature difference by land-based facilities
-- are met in American Samoa. Will our future electricity needs be powered by
our own blue ocean?
of the Territory is open ocean, of course. Only a minuscule 0.1% of the area consists
of dry land (all 7 islands
total only 76.1 square miles). The other 99.9%
marine portion consists of two main habitats -- the shallow coastal waters adjacent
to the islands (a'au, aloalo) and the deep waters offshore (vasa).
Shallow coastal habitats,
with their coral reefs and colorful fish, are quite limited in total area because
our islands slope steeply down into deeper water and depths of 2000 feet are reached
within 0.5-2 miles from shore. So, most of our coral reefs are restricted to a
narrow ring around each island. There is also some coral on the tops of several
offshore seamounts in the Territory.
might wonder, how is it that non-tropical oceans are much more productive? The
answer is, again, temperature. Away from the tropics, seasonal changes in water
temperature cause the water to mix. Winter temperatures cool the upper layer causing
it to sink and mix with the bottom layer, and when this occurs, some nutrients
are brought up to the surface. The nutrients in shallow sunlit waters stimulate
phytoplankton growth, thus fueling a more productive foodweb.
tropics, the 2-layer stratification of the ocean persists year-round because hot
sun keeps the surface layer warm. The tropical ocean has been called a 'biological
desert' for this reason. That's an exaggeration, of course, because all the tuna
out there are finding something to eat. And, many other species live out there
as well, from an occasional whale, dolphin, sea turtle or seabird, to numerous
species of fish and invertebrates such as jellyfish and shrimp-like crustaceans.
rest of our marine environment consists of deep blue ocean with a fairly flat
seafloor 2-3 miles below the sea surface. The reason for the blue color of the
ocean is an interesting one and it is a key factor to understanding our ocean
ecosystem, so we need to get technical for a moment. Water by itself is highly
transparent with a bluish tinge. What adds other colors to the ocean are, in large
part, small marine plant-like cells called phytoplankton. The more phytoplankton
in the water, the greener the water becomes. Phytoplankton require two main ingredients
to grow well: sunlight and nutrients (fertilizers). If they have both, they grow
in abundance. This, in turn, supports a productive food web: phytoplankton provide
food for the microscopic shrimp-like animals (zooplankton), and the zooplankton
provide food for the fish to eat.
Tropical oceans are not green because
conditions are generally not good for phytoplankton growth. Although phytoplankton
have all the sunlight they could ever want in the surface layer, nutrient levels
there are too low to support much plant growth. This occurs because the deep tropical
ocean is typically stratified into two layers with very different temperatures.
The sun heats up the surface layer, which is about 300 feet deep, to a pleasant
840 F, but the deeper layer remains a chilly 420 F. Because warm water is lighter
than cold water, the warm ocean water generally stays on top, the cold water stays
on the bottom. The two layers do not mix.
That's the rub. The bottom
layer is where the nutrients are, but because of the 2-layer stratification, the
nutrients can't get up to the surface layer where they are needed to combine with
sunlight for plant growth. So, conditions for phytoplankton are not very good
in the tropical ocean. The surface layer has lots of light but few nutrients,
while the bottom layer has lots of nutrients but no light. It's pitch black down
there. This arrangement doesn't support a very productive foodweb, so there are
generally fewer fish in tropical oceans than in non-tropical oceans.
6. Our deep blue
American Samoa is
much larger than you might think it is. The whole Territory covers 117,500 square
miles, which is about the size of New Zealand or the state of Oregon. The Territory
is big because we claim jurisdiction of the ocean that surrounds American Samoa,
from the shoreline out to 200 miles offshore. That is standard procedure throughout
the world (each country with marine coasts wants to protect its coastline and
marine resources from others). To be more precise, American Samoa has jurisdiction
over territorial waters out to 3 miles, while the US federal government maintains
control of the zone from 3 to 200 miles from shore.