Cephalopods in the Diet of Swordfish (Xiphias gladius) Caught off the West Coast of Baja California, Mexico

The lower beaks of 1,318 cephalopods from the stomach contents of 175 swordfish, Xiphias gladius, caught off the west coast of Baja California, Mexico, between 1988 and 1996 were analyzed. In total, 20 species of teuthoids, 4 octopods, and one vampyromorph were identified. Weights and lengths of cephalopods were estimated from the lower rostral lengths. Ommastrephid squids, primarily jumbo squid Dosidicus gigas of different maturing sizes, composed 60% by number and 82% by estimated weight. Three species of gonatids were identified and represented 22% by number. An unidentified species of Argonauta was the most abundant octopod, with 5.8% of the beak total. Ancistrocheirus lesueurii is recorded for the first time in the California Current. Distribution of cephalopods in the California Current and their size in the diet of other marine predators are discussed. The diet of swordfish was dominated by medium to large muscular squid species that probably are eaten in surface waters at night. Clarke (1966) noted that marine predators prey on species of cephalopods that often are poorly known. In fact, the study of cephalopod remains in the stomach contents of marine predators has contributed greatly to our knowledge of the distribution and ecology of these mollusks. Information on oceanic cephalopods in the diet of marine predators in the California Current and northeastern Pacific Ocean has come principally from studies on marine mammals, mainly odontocetes or toothed whales and pinnipeds. Squids recovered from the stomach contents of sperm whales, Physeter macrocephalus Linnaeus, 1758, from the Bering Sea and Gulf of Alaska were documented by Okutani and Nemoto (1964). Clarke and MacLeod (1980) identified cephalopod remains from 20 sperm whales caught off western Canada, and Fiscus et al. (1989) reported on beaks found in 175 specimens of the same predator off California. Mead et al. (1982) analyzed beaks from several Hubbs’ beaked whales, Mesoplodon carlhubbsi Moore, 1963, stranded in California and provided drawings of a pair of Gonatus sp. beaks. Cephalopods found in a short-finned pilot whales, Globicephala macrorhynchus Gray, 1846, salvaged off California were listed by Seagars and Henderson (1985) and Hacker (1992). The beaks of an unidentified gonatid squid collected from pilot whales are illustrated in Hacker (1992). Fiscus (1982) examined cephalopod remains recovered from the northern fur seal, Callorhinus ursinus (Linnaeus, 1758), and other marine mammals taken from California to the Pacific Science (2005), vol. 59, no. 1:25–41 : 2005 by University of Hawai‘i Press All rights reserved 1 This paper resulted from parts of the M.S. thesis of U.M. Thesis work was supported by a multinational grant from the Consejo Superior de Investigaciones Cientı́ficas (CSIC) in Spain and the Consejo Nacional de Ciencia y Tecnologı́a (CONACyT) in Mexico. Manuscript accepted 9 March 2004. 2 Corresponding author. 3 Departamento de Ecologı́a, Centro de Investigación Cientı́fica y de Educación Superior de Ensenada (CICESE), Ctra. Tijuana Ensenada km 107, Ensenada, Baja California, Mexico. Current address: Departamento de Aprovechamiento y Manejo de Recursos Acuáticos, El Colegio de la Frontera Sur, Unidad Campeche, Calle 10 61, No. 264, Col. Centro, 24000 Campeche, Mexico (phone: 52 981 816 4221 ext. 2406; fax: 52 981 816 5978 ext. 2102; e-mail: [email protected]). 4 Department of Invertebrate Zoology, Santa Barbara Museum of Natural History, 2559 Puesta del Sol Road, Santa Barbara, California 93105-2936 (phone: 805-6824711 ext. 318; fax: 805-569-3170; e-mail: fghochberg@