Comparative study of spawning pattern and reproductive potential of the Northern and Southern stocks of Argentine hake (Merluccius hubbsi)

Abstract

The reproductive biology of the Northern (Bonaerense) and Southern (Patagonian) stocks of M hubbsi in the Argentine Sea is analyzed, including information on spawning areas, estimates of abundance and size composition of spawning females, fecundity, spawning frequency and egg quality. Samples of Argentine hake were obtained during the period of peak reproductive activity; May and January for the Northern and Southern stocks, respectively. The size of the reproductive area for the Northern stock (35- 38ºS) was clearly smaller than the one estimated for the Southern population (43º 30´-46ºS), being 23,770 Km2 and 52,460 Km2 respectively. Spawning females from the Northern reproductive area were smaller (modal values between 35 and 40 cm TL) than those from the Southern stock (modal values between 38 and 50 cm TL), and they were also less abundant in number and had a lower spawning frequency (8 - 13 days and 5 - 7 days between partial spawning for the Northern and Southern stocks respectively). No differences in batch and relative fecundity between stocks were recorded (mean values of 526 and 530 hydrated oocytes g-129 ), but the dry weights of hydrated oocytes from females of the Northern group were higher (3.08 mg for 100 hydrated oocytes) than those of the Patagonian stock (2.84 mg)for the same total length range. The egg production during the month of peak spawning of the Northern group depended mostly on the smaller females (< 50 cm TL) and was in average 1 to 2 orders of magnitude lower than that estimated for the Southern stock (9 x1012 ? 22 x 1012 eggs and 692 x 1012 ? 1,295 x 1012 eggs for the Northern and Southern stocks respectively). Those differences in egg production and the high productivity and retentive characteristics described for the spawning area and nursery ground in Patagonian waters would justify the greater abundance and resilience of the Southern stock of Argentine hake. The low abundance of females in spawning capable stage observed during the reproductive season of the Northern group (autumn-winter), led us to postulate that currently it does not exist a pronounced reproductive peak in this stock similar to the one observed for the Southern hake group during the summer.