101

 Seasonal not production of Gambusia was estimated by

using the Allen curve method (Chapman, 1968), in which

average number of individuals per square meter on each date

is plotted as a function of average dry weight of

individuals that date. Integration of the function between

two dates represents productivity for that period. In this

study, estimating productivity from the Allen curve was

complicated by the existence of more than one period of

recruitment, so a modification of the method was devised:

two areas under the curve were delineated and summed.

Another method of calculating production was to subtract

the natural log of the standing stock (dry weight per

square meter) at the beginning of dispersion (early in the

wet season) from that just prior to concentration (at the

end of the wet season). This method was used to estimate

production rates of Mosquitofish, sunfish, gar, and

crayfish.

 The exponential equation approximates the growth of

fish under non-density limited conditions and where there

is an excess of food relative to consumption. This

equation is:



 Q = Qrt (18)


where Qo is initial weight, Qt is instantaneous weight, and

t is time. From the above equation the production rate, r,

can be calculated as follows: