TOLL and HESS: CEPHALOPODS IN DIET OF SWORDFISH 



65 



60- 



55- 



30 



X 



P 25-^ 



20- 



15 

 10 







0-9 20-29 „ „^40-49 „ 60-69 80-89 



10-19 30-39 50-59 70-79 90-100 



Figure 3. — Shrimp remains as percent of total stomach con- 

 tents by weight. 



0-9 20-29 40-49 60-69 80-89„„ „„ 



10-19 30-39 50-59 70-79 90-100 



Figure 4. — Illex spp. remains as percent of total stomach 

 contents by weight. 



DISCUSSION 



Swordfish in the Straits of Florida demonstrate 

 a clear predilection for cephalopods as prey, specif- 

 ically squids. Furthermore, the genus Illex consti- 

 tutes the single most important component in the 

 diet. At present, there are three nominal species 

 of Illex known from the western North Atlantic: 

 /. illecebrosus, I. coindetii, and /. oxygonius. 

 A recent revision (Roper et al. 1969) attempted to 

 stabilize the systematic positions of these 

 taxa. However, the same authors reemphasized 

 systematic and distributional complexities of this 

 polytypic genus, especially in the tropical western 

 Atlantic which includes the present study area. 

 Numerous specimens examined in this work had 

 the specific characters assigned to their nominal 

 species, however, systematic problems appear to 

 be most acute in the /. illecebrosus -I. coindetii 

 complex. Because of the tenuous systematic 

 and distributional aspects, as well as the 

 poor condition of much of the material, the 

 writers thought it best to deal with the group at 

 the generic level rather than possibly adding 

 to the underlying systematic and zoogeographic 

 confusion. 



Many teuthoids aggregate for feeding or repro- 

 duction (see Clarke 1966). The cephalopod prey in 

 this study included such aggregating squid as 

 Illex spp., Ommastrephes pteropus, Thysano- 

 teuthis rhombus, Onychoteuthis banksii, and 

 Histioteuthis sp. Additionally, Ornithoteuthis 

 antillarum and Tetronychoteuthis massyae prob- 

 ably behave similarly. Heavy swordfish predation 

 upon aggregating or schooling cephalopods is 

 similar to reported predation on schooling fishes 

 (Goode 1883; Tibbo et al. 1961). Tibbo et al. (1961) 

 and Scott and Tibbo ( 1968) noted the use of the bill 

 by swordfish to wound or kill prey. They suggested 

 that swordfish slash laterally with their bills, 

 while ascending or descending through a school of 

 prey. The present material contained numerous 

 decapitated squid and more frequently, oblique 

 slash marks on mantles thus supporting the 

 postulated foraging behavior. Furthermore, this 

 concurs with the knowTi horizontal orientation of 

 the pelagic squids listed above. Ommastrephids 

 and Thysanoteuthis have muscular mantles and 

 are powerful swimmers. Swimming ability of 

 swordfish does not appear to be a limiting factor in 

 the selection of cephalopod prey, as indicated 

 by the predominance of these organisms in the 

 diet of X. gladius. 



Ill 



