Distribution and biomass of the ommastrephid squids in the south-eastern Pacific in the early 1980s

The ecological investigations of ommastrephid squids were carried out in the open waters of the Southeast Pacific both outside the EEZ (3 degree N, 25 degree S) and inside the EEZ in 1979-1984 at 1460 light night drifting stations. Abundance and biomass (BS) of squid were estimated by the method of visual counting at light stations. The two dominant species Dosidicus gigas and Sthenoteuthis oualaniensis were present. In the Western Equatorial area (1 degree N-1 degree S, 95-106 degree W, 123,000 km super(2)) the BS in April-May 1981 was 940,000 metric t. The stock consisted of S. oualaniensis (75%) and D. gigas (25%). In the Eastern Equatorial area (a narrow zone between the boundaries of the EEZ, 3 degree N, 5 degree S, 280,000 km super(2)) the BS in same period was 300,000 t of D. gigas (83%) and S. oualaniensis (17%). In the open waters of the Peruvian region (5-25 degree S, from the EEZ boundary to 95 degree W, 1,020,000-1,630,000 km super(2)) squid distribution and BS were studied in different seasons during 1982. In April-June the BS was 1,770,000 t. In July-September the BS increased to 2,190,000 t and in October-December it was 2,020,000 t. D. gigas dominated in all seasons, its proportion of the total BS being 57%, 76% and 80% respectively. The biomass of D. gigas changed during the year in the opposite way to S. oualaniensis abundance fluctuations, therefore the total BS was relatively stable. D. gigas was particularly abundant in eastern and southeastern parts of the investigated area, but S. oualaniensis dominated in the western part. The latter formed no monospecific dense aggregations (>2500 kg km super(-2)). The dense aggregations of D. gigas were assessed as 175,000; 1,250,000; and 550,000 t in the mentioned seasons. The respective total BS (together with S. oualaniensis) in aggregations was 750,000; 1,550,000; and 1,100,000 t. These aggregations were located in the zone of divergence of the Peruvian Oceanic Current (17-22 degree S), and in the areas of meanders on the western periphery of this current.