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A rapid assessment of the sex ratio of the fiddler crab, Uca tangeri, was undertaken in two mangrove habitats on the Bonny River which were undergoing intense human impact as a result of dredging and urbanization activities. The contrasting adult sex ratios of 4:1 of male to female at Eagle Island and 1:2.6 at Rumuolumini and or juveniles showing 2.4:1 (Eagle Island) and 1:1.8 (Rumuolumini) were highly significant (χ2 test, P<0.05). This shows evidence of studies supporting deviation in Uca spp from the 1:1 proportion. Evidence of anthropogenic activity and intensive socioeconomic exploitation provided no explanation for the contrasting high deviation in ratio of males to females between Eagle Island and Rumuolumeni habitats. Megalopae settlement is evident but the physical, chemical and interspecific cues that determine gender balance are necessary for any intended future conservation planning.