Morphometric description of schools from two different stocks of the southernmost sprat Sprattus fuegensis

Sprattus fuegensis is a physostomous species of fish belonging to the family Clupeidae that inhabits the waters of the South Western Atlantic Ocean (SWAO), between 47 degrees and 55 degrees S. In the Pacific Ocean this species inhabits the Southern area of the Patagonia, 41 degrees-55 degrees S. Previous studies suggest the occurrence of at least two stocks of Fuegian sprat in the SWAO, the Patagonian stock and the Malvinas stock. In the present study, data obtained during several cruises carried out during the spawning season of the stocks were employed to describe the sprat schools inhabiting the two areas. The differences found among them are briefly discussed in the context of their respective habitat characteristics. The acoustic descriptors extracted from the two groups of schools revealed significant differences. The Malvinas Islands schools were larger in length, height, perimeter, area and volume and also were located deeper in the water column. The Patagonian schools were of smaller size but evidenced higher average school S-v values (similar to 6 dB). The Patagonian stock is associated with a larger number of denser but smaller schools, as compared with the Malvinas stock. Schools found in Malvinas area were composed of fish larger in size than those from the Patagonian coast. Trawl catches obtained in Patagonian waters ranged ca. 50-160 mm total length while fish caught in Malvinas Islands waters showed a body size of 90-220 mm TL. It is expected the information presented in this paper contributes to the knowledge of the sprat of the SWAO; one of the few fish populations that remain unexploited.