Estudo da variação espacial e sazonal da estrutura da população e aspectos reprodutivos de Plicofollis dussumieri (Bagre-do-mar de ponta preta) no estuário dos Bons Sinais-Zambézia

Abstract

This study examined the spatial and seasonal variations in the population structure and reproductive characteristics of Plicofollis dussumieri in the Bons Sinais Estuary (BSE), aiming to provide scientific support for sustainable management of the species. Monthly sampling was carried out throughout a year using two artisanal fishing gears (chicocota and beach seine) across three estuarine zones: Ilalane (upper estuary), Chuabo Dembe (middle estuary), and Marrubune (lower estuary), during both the dry and rainy seasons. Biometric analyses were conducted in the laboratory, including measurements of total length, body mass, and gonadal maturation stage. A total of 663 individuals were examined, with 53.5% belonging to the 9.7–14.7 cm length class. Most specimens were juveniles, with only a small proportion reaching the estimated length at first maturity (L₅₀). The mean total length differed significantly among zones (p < 0.05), being highest in the lower estuary (25.08 cm) and lowest in the middle estuary (12.51 cm). Seasonally, larger individuals were observed during the dry season (mean 13.36 cm), peaking in April (24.0 cm), while the smallest lengths occurred in the rainy season (mean 11.64 cm), particularly in March (6.1 cm). Analysis of sex ratio revealed a strong male bias (89.4%), which was statistically significant at the 5% level. Most individuals were in gonadal maturation stage I (82.1%), indicating a predominance of immature specimens and limited evidence of active spawning. No significant relationship was found between species abundance and environmental variables (temperature, salinity, water transparency). In conclusion, the P. dussumieri population in the BSE mainly consists of juvenile males, exhibiting low reproductive activity and apparent resilience to environmental fluctuations. These findings highlight the necessity for regulated exploitation to ensure the long-term sustainability of the species within this estuarine system.