Influência da seca prolongada na variação espacial, densidade e biomassa de tainhas (Mugil spp.) em estuários do semiárido brasileiro

Abstract

The semi-arid region of Brazil faced a severe drought between the years 2012 and 2016 causing an increase in the salinity of estuaries in the coastal region of the state of Ceará. Subsequently, between the years 2019 and 2020, there were rains above the historical average. During these periods, fish were collected with the aim of evaluating the potential effects of atypical rainy and dry periods on salinity variation in estuaries of the semi-arid region and, consequently, on the spatial distribution, density and biomass of four species of mullet (Mugiliformes: Mugil). Thus, in seven estuaries of the semi-arid coast, located in the state of Ceará, salinity measurements were performed and mullet specimens were collected with trawl and tarrafa net at different points and periods between the years 2014 and 2020. The univariate test of variance with covariates (ANCOVA) evaluated the influence of salinity (independent variable) on mullet densities and biomasses (dependent variables) in relation to the variables collection point in the river, season (rain or dry) and estuaries (covariates). When data were not normal, Friedman's test was used. The mullet densities in the Choró, Curu, Pacoti, Aracatiaçu, Aracatimirim and Malcozinhado River estuaries ranged from 0.2 ind./100m² to 100.5 ind./100m², showing significant correlation with salinity (r=0.29; p <0.05) and with higher densities (65%) at salinities above 30. The same pattern is observed for biomass (r=0.03; p < 0.05) with 33% of the highest densities above 30 salinity. In general, Mugil curema was the species that presented the highest density (100.5 ind./100 m²) and biomass (33,691 g/100m²) and Mugil liza the lowest abundance values (10.66 ind./100 m² and 141.5 g/100m²). The species Mugil rubrioculus and Mugil curvidens showed values between 13.8 ind./100 m² and 0.16 ind./100 m² for density and 70.4 g/100m² and 0.5 g/100m² for biomass. The salinity variation in the estuaries caused by the prolonged drought influenced the density and biomass of Mugil curvidens, Mugil curema and Mugil rubrioculus, indicating a positive relationship to salinity. The species Mugil liza did not show any relationship between density and salinity.