International Journal of Aquaculture, 2017, Vol.7, No.24, 159-165
161
The total mortality (Z) and fishing mortality (F) was calculated 0.87 and 0.40, respectively. Figure 2 showing the
catch curve was estimated by Z. In the present study deal with exploitation ratio (E) was estimated as 0.53. As the
E is <0.5, it was estimated stock of
S. gibbus
along southeast coast is under much fishing pressure. The asymptotic
length (L∞) and growth coefficient (K) have been calculated from the Ford-Walford plot was L∞ = 157.75 cm and
K = 0.06. The estimated was t
0
= -0.47 year. Total mortality (Z = F + M) was calculated using the method of
Beverton and Holt (1956) and natural mortality (M) using Pauly's formula (Pauly, 1978).
Bolbometopon
muricatum
the estimated growth rate was (K = 0.063) and, life span of
S. gibbus
was estimated for seven years.
According to Gulland (1971), if the E is >0.5 the stock may be considered as overfished. The results of Virtual
Population Analysis showed the F increases to a maximum at 40 cm (Figure 3).
Figure 2 Total mortality estimates by-catch curve method of
Scarus gibbus
Figure 3 Virtual population analyses
3.2 Age and growth
S. gibbus
, the large 264 trawlers in Tuticorin coast, the length ranges from 8.1 to 81 cm. The estimated of
asymptotic length (L∞) was obtained by Powell and Wetherall (1986) was calculated L∞ = 104.50 and K = 0.23
(Figure 2). Randall and Bruce (1983) has been studied reveal that the green humphead parrotfish,
Bolbometopon
muricatum
, estimated was 117 cm and weight was 46 kg. Family
Pomacentridae
, the related group of species, the
length group was 60 mm and age was 16-18 years (Fowler and Doherty, 1992). The following growth parameters
have been estimated by ELEFAN I method and it was L∞ = 104.50 cm and K = 0.23.
S. gibbus
the growth was
calculated 21.96 and 39.21 mm, the first and second year respectively (Figure 1).
