2 research outputs found
Нові підходи в керуванні процесами електронно-променевого зварювання
The Gambia Estuary, a “normal” estuary with a decreasing
salinity gradient from the mouth towards the head, is moderately exploited
by small-scale fisheries and does not receive any severe pollution from
either agriculture or industrial activities. Neither the Gambia River nor
its estuary are artificially impounded. As the last large West African
estuary free of major human disturbance, it is of considerable interest for
comparative studies on the effect of major environmental perturbations in
West African estuarine ecosystems. The aquatic environment and fish communities of the Gambia Estuary (about
250 km long) were studied by purse seine sampling at different periods in
the river cycle, covering all hydro-climatic seasons that are characteristic
of West African estuaries. Emphasis was placed on the diversity,
composition, structure and distribution of fish assemblages in relation to
fluctuations in physico-chemical factors such as water temperature, salinity
and turbidity. Results on the aquatic environment, mainly the salinity range
(from freshwater to 39) and dissolved oxygen (never a limiting factor for
fish in the estuary) and on the main characteristics of the fish fauna (high
diversity of life cycles, all the ecological categories represented)
indicated that the Gambia Estuary was free of major climatic perturbation
and reinforced the choice of this system as a reference for the study of the
effects of major perturbations on estuarine tropical fish communities
Juvenile fish assemblages in the creeks of the Gambia Estuary
A fyke net survey of the juvenile and small fish assemblage of the Gambia
estuary was conducted on three sampling occasions during the maximum
recruitment season, from May to November 2002. This is the first detailed
description of that particular component of the fish community in the Gambia
estuary.
The overall fyke net fish assemblage comprised 51 species, with a majority
of young individuals of large and medium size species and the adults of
small species. This assemblage is defined as the “small fish component of
the mangrove channels”.
The assemblage is dominated by true estuarine and certain marine species,
all able to complete their life cycle within the estuary. The sea spawning
species whose juveniles use the estuary mainly as a nursery ground, are not
very diverse or abundant during the recruitment season. They are limited to
the lowest part of the estuary due to the low salinity prevailing in the
middle and upper reaches during the rainy season. This suggests that extreme
seasonal variability (river flooding) in certain West African tropical
estuaries at the time of maximum recruitment by certain marine species may
reduce the nursery ground value for these taxa