DIURNAL VARIATION IN THE CATCHES OF SILVERBELLIES IN PALK BAY

Abstract

5\ comparison of the trawl landings from Palk Bay by day and night
fishing showed a marked variation in the catches of silverbellies between the two.
Another interesting feature noted was that even in night fishing, usually higher
catches of silverbellies were observed on full moon nights than on new moon
nights both in Palk Bay and Gulf of Mannar. From an analysis of the size
groups of Leiognathus jonesi and L. brevirostris caught, it was seen that the proportion
of smaller size group was greater in the night catches than in the day
catches whereas the proportion of the larger size group was greater in the day
catches than in the night catches. The diurnal variation in the catches of silverbellies
shows that they stay at the bottom during day time and at nights good
many of them migrate from there and rise to surface and sub-surface waters. This
and the instances of sharp difference in the catch rates observed between full
moon and new moon nights indicate a close link between light and the process
of migration in silverbellies. The probable cause for the variation in the size
groups in the catches by day and night fishing is pointed out. Fishing at the
surface, sub-surface and midwater levels at night by using suitable gear is suggested
for augmenting the production of silverbellies.