On the role of frontal systems of the Argentine Sea as spawning grounds for fishes

MACCHI, G.J.; ACHA, M.; PÁJARO, M.; MILITELLI, M. I.; RODRIGUES, K.

Lisboa

Simposio; Symposium Reproductive and Recruitment Processes of Exploited Marine Fish Stocks; 2007

Reproductive patterns of different species were analyzed searching for potential bio-physical couplings defining spawning ground selection. Information about maturity of ten finfish species (Merluccius hubbsi, Engraulis anchoita, Brevoortia aurea, Micropogonias furnieri, Cynoscion guatucupa, Percophys brasiliensis, Cheilodacthylus bergi, Ramnogaster arcuata, Micromesistius australis and Sprattus fueguensis) representative of different ecosystems of the Argentine Sea was obtained from different research cruises carried out between 1991 and 2005. Macroscopic and histological ovarian analyses were used to assign the maturity stages. The criteria employed to estimate incidence of spawning individuals was the presence of hydrated oocytes or new postovulatory follicles. Salinity and temperature data were collected with a CTD in different oceanographic stations. From the species analyzed, six showed the main spawning activity during spring and summer, one in midwinter, two at the end of this season and one in autumn. M. hubbsi showed two fishing stocks with spawning peaks in different seasons, one in spring- summer (Southern stock) and the other in autumn ? winter (Northern stock). Oceanographic analysis in areas where gravid females aggregate evidenced that spawning was spatially coincident with maximum salinity and/or temperature horizontal gradient (frontal zones). This fact was associated with the physical and biological properties of these systems, characterized by high levels of chlorophyll, showing them as productive places suitable for larval feeding and growth. Moreover, frontal dynamics could act as retention mechanisms reducing egg dispersion after spawning, while in other situations, they may enhance larval movement from reproductive areas to the main nursery grounds.