Salpa fusiformis populations of the North Atlantic

The occurrence and morphology of Salpa fusiformis along 30°W from 55 to 25°N are studied, resulting in the conclusion that two distinct populations can be recognized in this area. The northern, temperate population is characterized by a high number of fibers in the body muscles (averaging 52 for M I-VI in the aggregate form and 28 for M IV in the solitary form). The population occurred in high numbers during the spring of 1980; no diurnal vertical migration was observed. The southern, subtropical-tropical population is characterized by a low number of muscle fibers (averaging 39 in the aggregate form and 18 in the solitary form). Its abundance during the spring of 1980 was low and diurnal vertical migration conspicuous. At 38°N a few specimens were caught with intermediate muscle fiber numbers. This area coincided with a distinct minimum abundance of Salpa fusiformis.