International Journal of Marine Science 2016, Vol.6, No.27, 1-22
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the lean season. No crustaceans were identified either in the lean or peak seasons of the semi-industrial fishery.
During the lean season in the artisanal fishery, the crustacean and molluscan abundance was generally low as
compared to that from the peak season (Table 5).
Peneaus notialis
was not observed at all during the lean season,
but was present during the peak season in large quantities. In total, the shellfish species from the artisanal fishery
accounted for 0.39% of total catch in the lean season and 6.90% in the peak season, whereas that from the
semi-industrial fishery accounted for only 0.29% of the total catch during the peak season.
3.2.2 Diversity indices
Number of fish species observed ranged from 12 in the peak season of the semi-industrial fishery to 28 in the peak
season of the artisanal fishery (Table 6). Thus, the peak season of the semi-industrial fishery was the least species
rich with only 12 species, while the peak season of the artisanal fishery with 28 different species had the highest
number of species. In the artisanal fishery, ecological diversity indices measured (Margalef, Pielou,
Shannon-Weiner and Simpson indices) were all higher in the peak season as compared to the lean season.
However in the semi-industrial industry, although abundance (average number of individuals) was higher in the
peak season than the lean season, all diversity indices measured were lower in the peak season. The combined
diversity scores indicate that the peak season of the artisanal fishery was the most diverse (15) and the peak
season of the semi-industrial fishery the least diverse (4) season and fishery. The scores also revealed that the total
number of species identified did not necessarily relate to species diversity, as the lean season of the artisanal
fishery had a higher number of species but lower diversity as compared to the lean season of the semi-industrial
fishery (Table 6).
Table 6: Ranked diversity indices for both seasons in both fisheries [Highest score = 4 and least score = 1, in brackets]
Fishery/Seasons
Diversity indices
AFL
AFP
SFL
SFP
Shannon-Weiner
1.26(2)
1.93(4)
1.31(3)
0.87(1)
Pielou
0.53(2)
0.65(3)
0.67(4)
0.51(1)
Simpson
0.56(2)
0.78(4)
0.66(3)
0.45(1)
Margalef
1.82(3)
2.59(4)
0.72(2)
0.43(1)
Number of species
24.0
28.0
13.0
12.0
Total ranking value (4×4=16)
9.00
15.0
12.0
4.00
Legend
AFL = Artisanal fishery lean season
AFP = Artisanal fishery peak season
SFL = Semi-industrial fishery lean season
SFP = Semi-industrial fishery peak season
3.3 Significant physico-chemical parameters affecting biological variations
Out of the eighteen parameters measured, six parameters significantly (RELATE, r = 0.955, p < 0.05) explained
best the variations observed in the biological data, using the BVSTEP method in PRIMER 6 to relate fish
abundance and environmental data. These were total alkalinity, pH, carbonate ion concentration, nitrates,
phosphates and the Revelle factor.
The Principal Components Analysis (PCA) performed with these parameters for species abundance for both sites
and seasons yielded two principal components (eigenvalues > 1; Table 7) with a cumulative variance accounting
