International Journal of Aquaculture, 2017, Vol.7, No.24, 159-165
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Total mortality coefficient (Z) estimated was 0.87 (Figure 2). Natural mortality was calculated 0.47 (M) and
fishing mortality was 0.40. The exploitation rate (F/Z) estimated was 0.5 (Figure 4). Two peak spawning seasons
was calculated during the month of December and April (Figure 5). The total potential resource is being over
exploited from Tuticorin coast of Gulf of Mannar.
Figure 4 Relative yield-per-recruit and biomass-per-recruit
Scarus gibbus
(Lc /L∞ = 0.032. M/K = 2.04)
Figure 5 Recruitment pattern of
Scarus gibbus
Length calculated for different years using von Bertalanffy’s growth equation was plotted along with the observed
length of the same period which showed a general agreement in the growth pattern. This also showed high degree
of agreement with other methods employed. Ford-Warlford graph was constructed for
S. gibbus
by plotting Lt + 1
against Lt where Lt is the height of the animal at a particular age. Lt + 1 when intersected by a 45ºdiagonal from
the origin, L (length at infinity) was obtained and it was found to be 83.13 cm for this species. In the present study,
age and growth were studied through different methods. However, von Bertalanffy’s equation showed agreement
and gave reliable results. This heavy-beak parrot fish was found to have two recruitment seasons, one major
season, during December and a minor season during April (Figure 5).
3.3 Yield per recruit and biomass per recruit
S. gibbus
, the length at first capture (Lc) was 21.96. The relative yield per recruit and biomass per recruit was
calculated 0.03 and 2.4. The plot of yield per recruit (Y/R) against E is shown in Figure 6. The maximum Y/R was
