El Niño Southern Oscillation and spatial-temporal variability of the nominal performances of swordfish (Xiphias gladius) in the southeastern Pacific

Abstract

Swordfish (Xiphias gladius) is a highly migratory pelagic species, found in tropical, subtropical and temperate regions. In the Pacific Ocean, several studies have linked their wide latitudinal distribution (50°N-50°S) to environmental variables, since food is abundant along the frontal zones where currents or water bodies converge. In the southeastern Pacific, the subtropical anticyclone positively forces ocean temperatures along the west coast of South America, decreasing pole ward from the subtropical latitudes due to the El Niño Southern Oscillation. Environmental data from remote sensing enabled us to study changes in the spatial position of the 18°C isotherm in relation to spatial-temporal changes in swordfish nominal fishing yields (CPUE) of industrial longline fleet in the coast of Chile. Correlations were obtained between the latitudinal gravity center (LGC) of CPUE and the latitudinal position of the 18°C isotherm, between the latitudinal position of the 18°C isotherm and the area bounded by the 17°C isotherm, as well as between El Niño 12 index and the latitudinal position of the 18°C isotherm. At a seasonal level, the 18°C isotherm moves south of 37°S at the beginning of the year, reaching 25°S in August. This pattern occurs in a similar way to the area bounded by the 17° and 18°C isotherm. Two phases were observed in the swordfish CPUE, with 0.65 ± 0.06 kg per hook since mid-April to early June, and 0.37 ± 0.05 kg per hook from early September until late November.