International Journal of Marine Science 2016, Vol.6, No.44, 1-8
5
Fig.5. Length at age of
S. guttatus
in north east coast of India Fig.6. Recruitment pattern of
S. guttatus
in east coast of India
Fig.7. Virtual Population Analysis (VPA) of
S. guttatus
in the east coast of India
The L∞ and (Z/K) obtained by the Powell- Wetherall method were found to be 45.51 and 0.404 respectively. The
mortality parameters such as natural mortality (M), fishing mortality (F) and Total mortality (Z) were 1.43, 1.27
and 2.70 respectively. The longevity of the species was worked out to be 2 years. Taking the L∞ = 64.6, K = 0.97
and t
0
= -0.1329 the length of the species after 0.5 year, 1 year, 1.5 year and 2 years was estimated to be 29.6 cm,
43.1 cm, 51.3 cm and 56.4 cm respectively(fig.5). It could be observed that during the first six months the growth
rate of the species was the maximum (4.9 cm/month). It decreased henceforth, 2.2cm/month during the seventh -
twelfth month, 1.4cm/month during twelfth- eighteen months and 0.9 cm/year during eighteen to twenty four
months period. Some biological parameters of the species are given in table 3.
Recruitment pattern
The recruitment pattern (fig.6) indicated that the species spawns throughout the year with peak spawning during
January to June.
Virtual population analysis
The virtual population analysis (VPA) has shown that the mortality due to natural causes alone was up to 28cm
(fig.7). The fishing pressure started at 28.1cm and increased steadily thereafter up to 58.1 cm midlength. The
maximum fishing mortality of 2.4 was recorded at size of 43.5 cm.
Food and feeding
The feeding intensity showed that 56.2% stomachs were empty followed by half full (18.3%), full stomach
(11.8%), quarter full (8.6%) and three fourth full (5.1%), fig.8. The gut content analysis revealed that these fishes
are piscivorous in nature and the dietary composition in the order of preferences are anchovies (45%), sardines
(45%), shrimps (3%), upenoids (3%), squid (2%), lizard fish (1%) and silverbellies (1%), fig.9.
