Spawning frequency and batch fecundity of Brazilian menhaden, Brevoortia aurea, in the Río de la Plata estuary off Argentina and Uruguay

Abstract

Brazilian menhaden, Brevoor tia aurea, is the only species of the genus Brevoortia in South American Atlantic waters and is abundant in the Río de la Plata estuary. We found that B. aurea in this area spawns almost exclusively in this estuary. We studied the temporal and spatial reproductive pattern of this menhaden and related the pattern to the major hydrographic features of the region. We based evidence of spawning activity on the presence of females with hydrated oocytes and on the occurrence of menhaden eggs in plankton samples. Our results show that B. aurea spawn during virtually every month of the year, but that they spawn mainly from September (late winter) to January (early summer). In the Río de la Plata estuary, spawned eggs occur in a thermohaline range of 13–23°C and 10–25 psu, mainly in stratifi ed waters. Brevoortia aurea spawn very near the bottom salinity front, probably in a convergent fl ow between the riverine and estuarine waters that helps to retain eggs. In contrast to menhaden of the northern hemisphere (B. tyrannus and B. patronus), which spawn offshore and which drift during early life history stages, Brevoortia aurea in the Río de la Plata estuary are spawned and held in estuarine waters near spawning sites. The latter reproductive pattern is also shared by Micropogonias furnieri (whitemouth croaker), the most abundant fi sh species in the area.