|dc.contributor.author||Bayley, Peter B.||
|dc.description.abstract||A 2.5 year field study designed to estimate production of
fish in the Amazon river provides a basis for
understanding the fishery and certain features of
floodplain ecology. Intensive sampling with a fine-mesh
seine net throughout the hydrological cycle in a variety
of floodplain habitats revealed the seasonal spawning
sequences of many species, allowing identification of
cohorts and estimates of early growth from the sequential
samples. Using a block net and marked fish in the
habitats sampled routinely, the efficiency of the seine
net was estimated for various species groups and sizes.
Thus seine catches could be converted to biomass density
estimates. The overall estimate of fish and decapods was
160 gm-2 with 95% confidence limits of ±24. Growth of
individual species appeared unaffected by the biomass of
potentially competing species when the water was rising,
and only two out of eleven species suggested
density-dependent growth (at p<.05) during falling water.
A strong seasonal variation in growth rate was observed.
A multispecies growth function which depends on weight,
maximum weight of species, and hydrological season was
derived from the growth rates of 14 common species.
Fish plus decapod production averaged 280 gm-2yr-l, based
on the biomass estimates and growth function. The
estimated phytoplankton primary productivity of 290
gCm-2yr-l is insufficient to sustain the fish
productivity, and the importance of macrophytes was also
evident from the gut contents of common species.
The biomass distribution when plotted in logarithmic
length intervals increased sharply with length.
Non-conformity with the Sheldon spectrum for pelagic
systems could be explained by many fish feeding on
extremely small particles (fine detritus feeders) or very
large particles (macrophyte herbivores). However, the
prey to piscivore biomass ratio varied from 1 . 2 to 1.3,
which was similar to Kerr's (1974) interpretation of the
Sheldon spectrum. Transfer efficiencies of 37% and 39% were estimated for
two successive trophic levels, indicating a high predation
efficiency and growth efficiency. The similarity in
biomass ratios and predation efficiencies between the
central Amazon and those estimated for pelagic systems is
not paralleled by similar transfer efficiencies which are
apparently much lower in pelagic systems. This implies
higher gross growth efficiencies in Amazon fish which may
be due to the higher prey/predator length ratio of .25.
The system thus appears to be very efficient, yet only
2.7% of the total productivity is taken as yield by man in
a more exploited part of the basin. It is concluded that
the high predation efficiency leaves limited surplus
production from lower trophic levels to support an
expanded fishery, unless the latter can be managed in such
a way as to exploit all piscivores, many of which have low
market value at present.||en_US
|dc.title||Central Amazon fish populations: biomass, production and some dynamic characteristics||en_US
|dc.contributor.department||Department of Oceanography||en_US
|dc.contributor.degree||Doctor of Philosophy||en_US