Environmental Engineering Reference
In-Depth Information
larger range of habitat types (e.g., wetlands, oxbows, small side channels,
and open channels with high water velocity).
At times, samples taken in large-order streams
can have few or no fish species, but the ob-
served maximum number of fish species per
sample is generally higher in larger rivers.
Within basins, factors such as flooding,
pollution, turbidity, reservoirs, channel mod-
ifications, and exploitation by humans all
can alter the numbers and types of fishes
that are found. For example, in large rivers
in which reservoirs have been constructed
without fish ladders, species that move up-
stream to spawn can be excluded from up-
river areas, and the riverine fishes are re-
placed mostly by a lentic fish assemblage in
the reservoirs. Heavily polluted rivers, par-
ticularly those in which O 2 levels are very
low, support few or no fishes.
Within a stream segment or reach or
within a lake, the type of habitat present can
be very important. Any angler knows about
specific areas that fish are more likely to in-
habit. In streams, for example, cut banks,
woody debris, and deep pools all are places
where fish may congregate. Humans tend to
remove habitat structure, and much effort
has been made in many lakes and streams to
restore habitat that is essential to maintain-
ing a diverse fish assemblage and a produc-
tive fishery.
Restoration of streams and lakes requires
consideration of habitat characteristics that
lead to successful recovery of fish biodiversity
(National Research Council, 1992). The eco-
logical basis for river management must con-
sider what constitutes a natural hydrological
regime (Petts et al., 1995). Restoring physical
structure to stream channels may include wing
deflectors, low dams, placement of debris,
and other measures (De Jalón, 1995). Boat
traffic may also need to be controlled to de-
crease turbidity and wakes that may interfere
with reproduction (Murphy et al., 1995).
Restoration or habitat enhancement are also
practiced in lakes and reservoirs. Measures
include increasing cover for small prey fish
and juvenile fish of larger species and altering
the hydrological regime to match spawning
requirements of desirable fishes.
Sidebar 21.1.
Fishes in the Forest
Many fishes associated with the Amazon River
drainage are dependent on annual flooding of
the riparian forest (Goulding, 1980). The Amazon
and its tributaries flowing through tropical forest
annually flood the low-lying areas around the
river channels, allowing fish access to the forest
floor, and temporarily connecting many small
ponds and lakes with the main river channel.
The total number of Amazonian fish species may
be between 2500 and 3000, and a diverse fish as-
semblage forages in the floodplains. Some of the
species move from the main river into tributaries
to spawn, and others move from the flooded for-
est through the tributaries to the main river chan-
nel to spawn. These migrations allow predatory
fishes and local fisherman to capture spawning
fish as they move predictably in large schools
through specific places during specific times.
A most unusual group of fishes has evolved
to eat fruits and seeds. These frugivorous fishes
are confined almost entirely to South America.
In a coevolutionary response, some of the ri-
parian forest species have evolved fruits that
are dispersed by the fishes. These trees and
shrubs fruit during the flooding season, and
their fruits are under or near the water surface.
Fishermen take advantage of the feeding habits
of the frugivores and bait their hooks with fruits
that are preferred by the fishes.
Other fishes are seed predators and crush,
consume, and digest seeds. Seeds form a sig-
nificant proportion of the diet of some species
of piranhas ( Serrasalmus spp.), which are
known to most people as aggressive animal
predators. These fishes can have impressive
jaws and teeth that are adapted to breaking
the hard shells protecting nuts and seeds.
The fishes in the forest provide a clear ex-
ample of the linkage between riparian wet-
lands and production of fishes. Many of these
fish species have an absolute requirement in
their life cycle for the seasonal availability of
resources in the flooded riparian zone. Some
plants benefit from the interaction as well.
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