ABSTRACT
Species diversity, richness and composition of fish in bottom-trawling were investigated
off the Namibian coast between Oranjemund and Henties Bay. Sampling followed a
systematic transects design, along latitude gradients (28-22oS) at different seafloor
depths (100-500m). In total 18 transects were sampled containing 105 stations. At each
trawled station the whole catch was sorted into species type and the total body mass (kg)
of each fish species was recorded. A total of 91 fish species were sampled in the study
area. Environmental factors, in particular bottom water temperature, dissolved oxygen
and salinity were recorded automatically by the CTD instrument. Results indicated
significant differences in means of fish species diversity (F = 14.01, df = 4, p < 0.001)
and richness (df = 4, p < 0.001) at different seafloor depths. Deeper areas were more
diverse than shallower area. With regard to latitudinal transect gradients significant
differences were observed in means of fish species richness (df = 6, p < 0.05) but not
diversity (F = 1.28, df = 6, p > 0.05). The hierarchical cluster analysis on species
presence/absence data separated the fish species composition into six groups, formed at
38% similarity level. Indirect gradient analyses indicated a complex interaction of
gradients which have influenced the pattern of species composition. The direct gradient
analysis indicates significant influence of water temperature (F = 4.03, p < 0.05) and
salinity (F = 1.55, p < 0.05) on species composition at 100m and 200m seafloor depths.
Differences in species diversity and richness of fish at seafloor depths might be a result
of absence of disturbances by bottom-trawling at shallower depths. Insignificant
differences in species diversity along latitudinal gradients indicate inconsequential
effects of global latitudinal trends off the Namibian coast. It was concluded that
environmental variabilities off the Namibian coast influence fish species composition.
Nashima, F (2021). Effects Of Environmental Variability On Fish Diversity And Composition Along The Southern Namibian Coastline During Summer. Afribary. Retrieved from https://track.afribary.com/works/effects-of-environmental-variability-on-fish-diversity-and-composition-along-the-southern-namibian-coastline-during-summer
Nashima, Festus "Effects Of Environmental Variability On Fish Diversity And Composition Along The Southern Namibian Coastline During Summer" Afribary. Afribary, 28 Apr. 2021, https://track.afribary.com/works/effects-of-environmental-variability-on-fish-diversity-and-composition-along-the-southern-namibian-coastline-during-summer. Accessed 16 Nov. 2024.
Nashima, Festus . "Effects Of Environmental Variability On Fish Diversity And Composition Along The Southern Namibian Coastline During Summer". Afribary, Afribary, 28 Apr. 2021. Web. 16 Nov. 2024. < https://track.afribary.com/works/effects-of-environmental-variability-on-fish-diversity-and-composition-along-the-southern-namibian-coastline-during-summer >.
Nashima, Festus . "Effects Of Environmental Variability On Fish Diversity And Composition Along The Southern Namibian Coastline During Summer" Afribary (2021). Accessed November 16, 2024. https://track.afribary.com/works/effects-of-environmental-variability-on-fish-diversity-and-composition-along-the-southern-namibian-coastline-during-summer