Английский язык: Сборник текстов и упражнений. Дьякова Н.П. - 32 стр.

                              UNIT 2
               FISHERIES AND ECOLOGICAL PROBLEMS


                                    Text 10
                                   EСОLOGY

     Ecology is the science of interrelationships between living organisms and
their environment. Fishes are the major vertebrates of freshwater and marine en-
vironments. Although some amphibians, reptiles, birds and mammals also live in
aquatic environments, they do not have the enormous variety and ecological im-
pact of fishes. Once fish become large enough to actively swim, they become
members of the nekton community and actively control their place in time and
space within the water column. Fishes are capable of vast migrations and need
not drift with the currents, as do plankton. Shellfishes such as oysters and crabs
are also important fisheries resources. Although we recognize that oysters and
crabs are not fishes, the types of information needed to manage them (standing
crop, birth; death and harvesting rates) are similar to those collected for fishes.
To properly manage our fisheries, we need to understand the attributes of har-
vested species.
     From an animal’s point of view, obtaining food without being eaten is criti-
cal-it must be able to gather enough food to meet its energy requirements and
reproduce the next generation, but not fall prey to another animal. To accom-
plish this, an aquatic animal may change its morphology and preferred habitat
during its life time. Aquatic animals are subject to many environmental influ-
ences, including the availability of food, which is necessary for a population to
demonstrate high growth and reproduction. The animal also must find favoura-
ble temperatures and oxygen conditions, while avoiding predators, diseases and
parasites.
     As we examine environments from small ponds through rivers, lakes and
oceans, understanding the factors controlling fish production become progres-
sively more difficult. In small ponds, food availability often controls fish pro-
duction, but the factors that control the survival of young oceanic fishes and
their ultimate productivity is one of the greatest challenges to the fisheries scien-
tist. Only certain fishes, shellfishes and algae have the characteristics necessary
for harvesting by humans. They must be abundant and, at some time during their
adult life, should be concentrated in a predictable area so they are accessible to
fishing gear. A species value as human food depends on its acceptability in our
diet, nutritional quality and accessibility. Organisms that are highly valued by
one society may be ignored or considered repugnant by another. Many species
having no value as human food are fished for reduction to fish meal used in li-
vestock and aquaculture feeds. These species constitute some of our largest fi-
sheries in terms of catch weight. Ecology is best studied within the context of
ecosystems, rather than considering only the species of interest. An ecosystem
includes all of the interacting organisms and physical-chemical components.
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