Abstract

The diet of swordfish is analyzed in three oceanic fishing zones off central Chile during winter 2003, testing the hypothesis that the body size of prey individuals significantly increases with the size of the predator, and that the number of prey individuals decreases with increase in their size. The study was based on 48 stomachs of Xiphias gladius found to contain identifiable prey remains. The analysis was made using quantitative descriptors of frequency and occurrence of prey items. Diets in the different sampling zones were ranked by frequency and occurrence of prey species. Also determined were the proportions of fishes and cephalopods in the diet, and number and sizes of cephalopods related to body lengths of the swordfish. Results of the study showed that the swordfish preyed primarily on squid, and secondarily on fishes. Dosidicus gigas was the main prey within two of the sampling zones (F=100 and 75%), and Onychoteuihis banksii in one zone (F = 71%). The number of prey individuals was not significantly related with the body length of X. gladius, but low correlation was noted between swordfish body size and prey size. The diet of X gladius varied only according to the fishing zone, and was not related to the size of the predator. The habitat of the predator is one of the most important factors to be considered in the study of its' diet, since variation in the habitat may affect the population dynamics of both prey and predator.