CEPHALOPODS IN THE DIET OF THE SWORDFISH, XIPHIAS GLADIUS 



FROM THE FLORIDA STRAITS 



Ronald B. Toll and Steven C. Hess' 



ABSTRACT 



An analysis was conducted on the cephalopod remains from the stomachs of 65 swordfish, Xiphias 

 gladius. from the Florida Straits. Results indicated that cephalopods contribute a large proportion of 

 the total ration of food items, accountmg for over 9(y* of total weight of contents in 690 of the stomachs 

 Of these, ommastrephid squid of the genus Ille.x represented the single most important prey items. In 

 total, 15 species of cephalopods were encountered, consisting of 13 teuthoids and 2 octopods. This 

 previously unrecognized diversity confirmed the earlier postulated opportunistic feeding strategy of 

 X. gladius. Cephalopod, fish, and crustacean remains are reported in terms of frequency of occurrence 

 and biomass. Analysis of the vertical distribution of cephalopod prey indicated that .swordfish feeding 

 IS most concentrated in epipelagic and upper mesopelagic waters. Comparisons with feeding studies on 

 billfishes from the western North Atlantic indicated that istiophonds may rely more heavily on finfish 

 prey than squid in contrast with the present findings for X. gladius. Also, octopods may contribute a 

 greater proportion of the cephalopod component of total ration in the istiophorids than in X. gladius. 



Analysis of stomach contents of many marine 

 teleosts, mammals, and birds (Bouxin and 

 Le Gendre 1936; Clarke 1966; Rancurel 1970, 1976; 

 Dragovich and Potthoff 1972; Imber 1973, 1975; 

 Perrin et al. 1973; Clarke and MacLeod 1970, 1976; 

 Mercer 1974) coupled with estimates of cephalopod 

 biomass (Voss 1973) suggest a key role of cephalo- 

 pods in oceanic food webs. Nevertheless, few 

 thorough studies have been conducted that have 

 analyzed cephalopod remains, both qualitatively 

 and quantitatively (see Voss 1953; Rees and Maul 

 1956; Jolley 1977; Matthews et al. 1977; Morejohn 

 et al. 1978). Oceanic vertebrates are often more 

 efficient collectors of cephalopods than available 

 oceanographic gear (Clarke 1966). Therefore, 

 information from stomach content analyses can 

 supplement and refine existing knowledge of the 

 biology of both prey and predator. 



Cephalopods represent a major element in the 

 diet of the swordfish, Xiphias gladius Linnaeus 

 (Maksimov 1969). Yet, investigations of swordfish 

 diet, commencing with Fleming (1828), yield little 

 data concerning the trophic relationship between 

 this predator and cephalopod mollusks. Acquisi- 

 tion of 65 swordfish stomachs allowed investiga- 

 tion of feeding ecology with emphasis on aspects of 

 the biology and systematics of cephalopod prey. 



'Division of Biology and Living Resources, Rosenstiel School 

 of Marine and Atmospheric Science, University of Miami, 4600 

 Rickenbacker Causeway, Miami, FL 33149. 



HISTORICAL RESUME 



The feeding ecology of X. gladius is poorly 

 understood, not only because of a general paucity 

 of studies concerning xiphiid predation, but per- 

 haps more importantly, from a lack of studies 

 by invertebrate specialists dealing with inverte- 

 brates consumed by swordfish (e.g., mollusks, 

 crustaceans). In contrast, stomach content 

 analyses made by ichthyologists have provided 

 reasonably good specific-level diagnoses of 

 fish remains. A brief summary of studies that 

 contain information on cephalopod remains from 

 X. gladius stomachs is provided here. 



Goode (1883) cited Fleming's ( 1828) report of the 

 remains of Sepiae from a swordfish stomach. 

 Goode also noted the occurrence of squid man- 

 dibles and speculated they were from the loliginid 

 squid, Loligo Pealii (= L. pealei). In addition, 

 Goode observed that stomach contents of sword- 

 fish from the western Atlantic were ". . . for the 

 most part of the common schooling species of 

 fishes." Rich (1947) noted a set of large beaks 

 ("perhaps Architeuthis") from a Xiphias har- 

 pooned on the northern Georges Banks. Bigelow 

 and Schroeder (1953) noted a specimen of Ilex 

 ( = Illex) from the stomach of a swordfish har- 

 pooned off Halifax, Nova Scotia, and commented 

 that squid may, at times, form the chief com- 

 ponent of the swordfish diet. Yabe et al. (1959) 

 reported squid (mantle length 20-40 mm» and 



Manuscript accepted July 1981. 



FISHERY BULLETIN: VOL. 79. NO. 4, 1981. 



765 



