Abstract:
Population dynamics of dominant fish species in two lowland reservoirs of Sri Lanka
were studied based on length-based stock assessment methodologies, as implemented in FiSAT II
software. The estimated growth parameters of Oreochromis mossambicus in Udawalawe and
Chandrikawewa reservoirs and those of O. niloticus and Labeo dussumieri in Udawalawe
reservoir fall within the growth space of auximetric plots of cichlids and cyprinids indicating
reliability of estimates. In the Chandrikawewa reservoir where O. mossambicus exhibited faster
growth, increased fishing pressure might lead to push the population towards the extreme of ‘rselected’
life strategy so that continuation of the fishery at the present exploitation level is
advisable. Relative yield-per-recruit (Y’/R) analyses indicate that for O. niloticus and L.
dussumieri in Udawalawe reservoir, exploitation levels can be increased to optimize Y’/R.
However, since these two species and O. mossambicus are caught in the same fishing gear,
exploitation rate for O. niloticus and L. dussumieri has to be increased to a level that would not
lead to over-exploitation of O. mossambicus stock.