Size distribution of the jack Chloroscombrus chrysurus (Linnaeus) (Actinopterygii, Carangidae) in a tropical bay at Southeastern Brazil

Abstract

Chloroscombrus chrysurus (Linnaeus, 1766) is the most abundant representant of the Carangidae family in the Sepetiba bay, a c.a. 450 km² semi-closed coastal area in the Southeastern Brazil. We analyze fish (number, weight and size) and environmental data to assess the part of life history of this species in tropical embayment environments. Fish sampling were taken in triplicates by monthly bottom trawls, in three bay zones (inner, middle and outer), defined according to a spatial gradient of depth and salinity. Juveniles were firstly caught in the inner bay zone measuring 30-90 mm total length - TL (mode = 60 mm TL) in Spring. Then they move toward the middle and outermost part of the bay in Summer-Autumn (120-180 mm TL), following a seaward migration to join the adults during the Winter. No early juveniles were recorded recruiting at sandy beaches of the Sepetiba bay, although spawning has been reported to take place at nearby coastal areas, with eggs and larvae penetrating into the innermost bay zones. At least two yearly classes coexist in the bay during the first two years. Environmental gradient of temperature, salinity, transparency, dissolved oxygen and depth are poor predictors of fish numbers and biomass, and the significant negative correlation with salinity and depth only reflect the large numbers of juveniles in the innermost part of the bay, where influence of continental drainage and sediment deposition is higher.