Environmental conditions associated with swordfish size compositions and catches off the Chilean coast

Abstract

Multivariate analyses were applied to explore the relative influence of environmental factors on swordfish ( Xiphias gladius ) size compositions and catches off Chile. A first analysis was applied to a commercial fishing data base made up of biological-fishery and environmental records from 343 fishing sets performed between 2000 and 2002 by two longline vessels. Furthermore, a data base of fishing research cruises over the Cordillera de Nazca was analyzed; this set consisted of biological-fishery and environmental satellite information recorded for 43 fishing sets done in summer and winter 2003 and autumn and spring 2005. Principal component and hierarchical classification analyses were applied to seven environmental variables (Latitude, Longitude, Sea surface temperature, Chlorophyll a concentration, Sea surface height, Sea surface salinity, Bathymetry), all of which may affect the distribution of swordfish size compositions and catches. The analyses indicate four spatial groups representing specific latitudinal locations and typologies of environmental conditions associated with the swordfish size compositions and catches in the study area. Swordfish were caught within a range of SST that varied from 16 to 22oC, with larger catches given smaller SSTs, greater chlorophyll concentrations, and higher latitudes. A latitudinal gradient in size composition is affirmed, with juvenile specimens associated with warmer conditions, greater salinity, lower chlorophyll concentrations, and lower latitudes. The geographic distribution of the recruitment zone is associated with the Cordillera de Nazca marine area.