ANKKNHKANltT: FOOH HABITS OK SKIIMACK TINA 



the stomachs of skipjack, compared with larger 

 scombrids. may be a result of smaller gill raker gaps 

 in skipjack (Magnuson and Heitz 1971). 



The importance of other fishes as food for western 

 Atlantic skipjack tuna observed in this study has 

 been previously reported. Dragovich (1970) found a 

 predominance of fish in the stomachs of skipjack 

 caught off the eastern United States and the Carib- 

 bean. Suarez-Caabro and Duarte-Bello (1961) found 

 that fishes constituted 75% of the total volume, 

 followed by squid (23%) and crustaceans (2%), in the 

 stomachs of Cuban skipjack. Zavala-Camin (1981) 

 observed that fish constituted 38.9%, crustaceans 

 22.2%, and mollusks 2.8% of the total stomach 

 volume of Brazilian skipjack. 



CONCLUSIONS 



The multiplicity of prey found in this as well as 

 other studies indicates that tunas are perhaps non- 

 selective feeders, and stomach contents are probably 

 determined by prey availability (Hotta and Ogawa 

 1955; Alverson 1963; Batts 1972; Perrin et al. 1973; 

 Argue et al. 1983). Therefore, if the larval and 

 juvenile skipjack were available in significant 

 numbers, then one would expect them to occur in the 

 diet of the adults. 



Their absence in the diet was caused by two possi- 

 ble results. First, the young remained among the 

 unidentified portion of the stomach contents; 

 however, skipjack tuna have distinctive vertebral 

 characteristics which were probably not discounted 

 in the analysis (Potthoff and Richards 1970). Second, 

 the adults did not spawn in the study area. Young 

 skipjack should be found in the stomach contents of 

 spawning adults (Argue et al. 1983). Goldberg and 

 Au^ found no evidence of spawning in skipjack col- 

 lected from the Brazilian fishery. These results are 

 consistent with the absence of larval and juvenile 

 skipjack in the diet of the adults in this study. 



The southernmost distribution boundary for larval 

 skipjack tuna is the 24 °C surface isotherm (Argue et 

 al. 1983). Matsuura (1982) found no larval skipjack in 

 ichthyoplankton surveys south of lat. 21 °S in this 

 area, where temperatures range from 21° to 24°C 

 (Evans et al. 1981). 



^Goldberg, S. R., and D. W. K. Au. 1983. The spawning 

 schedule of skipjack tuna from southeastern Brazil as determined 

 from histological examinations of ovaries, with notes on spawning in 

 the Caribbean. Prepared for the International Skipjack Year Pro- 

 gram conference of the International Commission for the Conser- 

 vation of Atlantic Tunas. June 21-25, 1983, Tenerife, Canary 

 Islands, Spain, 31 p. Manuscript in preparation; Department of 

 Biology, Whittier College, Whittier, CA 90608. 



These results are consonant with those of Argue et 

 al. (1983); juvenile skipjack tuna were absent from 

 samples of adult stomachs taken in subtropical south 

 Pacific waters. The adult skipjack in this investiga- 

 tion did not feed on their young. The absence of 

 cannabilism suggests that larvae and juveniles were 

 not significantly abundant to serve as forage of the 

 adults, and therefore probably do not occur in this 

 cooler southern water. 



ACKNOWLEDGMENTS 



I wish to thank Ronald Rinaldo for organizing the 

 collection of stomachs from skipjack tuna landed in 

 Puerto Rico and Brazil. Silvio Jablonski (SUDEPE, 

 Brazil), Eugene Holzapfel (NMFS, Puerto Rico), and 

 their employees were responsible for the collection 

 and shipment of the skipjack tuna stomachs. 



Gareth Nelson, Richard Rosenblatt, Kurt Schaef- 

 fer, and Betsy Stevens assisted in the identification 

 of the fishes. The euphasiid was identified by Ed- 

 ward Brinton. Robert Olson assisted in the identifi- 

 cation of cephalopod beaks. Angeles Alvarino 

 assisted in the identification of other invertebrates. 



Thanks to Andrew Dizon, John Graves, Ronald 

 Rinaldo, Robert Olson, and Kurt Schaeffer for their 

 criticisms and suggestions in reviewing this paper. 



LITERATURE CITED 



Alverson, F. G. 



1963. The food of yellowfin and skipjack tunas in the eastern 

 tropical Pacific Ocean. [In Engl, and Span.] Inter-Am. 

 Trop. Tuna Comm. Bull. 7:293-396. 

 Argue, A. W., F. Conand, and D. Whyman. 



1983. Spatial and temporal distributions of juvenile tunas from 

 stomachs of tunas caught by pole-and-line gear in the central 

 and western Pacific Ocean. Tuna and Billfish Assessment 

 Programme Technical Report No. 4. South Pacific Commis- 

 sion, Noumea, New Caledonia. 

 Batts, B. S. 



1972. Food habits of the skipjack tuna. Katsuwomm pelamis, 

 in North Carolina waters. Chesapeake Sci. 13:193-200. 

 Dragovich, A. 



1969. Review of studies of tuna food in the Atlantic Ocean. 

 U.S. Fish Wild!. Serv., Spec, Sci. Rep. Fish. 593, 21 p. 



1970. The food of skipjack and yellowfin tunas in the Atlantic 

 Ocean. Fish. Bull., U.S. 68:445-460. 



Dragovich, A., and T. Potthoff. 



1972. Comparative study of food of skipjack and yellowfin 

 tunas off the coast of West Africa. Fish. Bull., U.S. 70:1087- 

 1110. 

 Evans, R. H., D. R. McLain, and R. A. Bauer. 



1981. Atlantic skipjack tuna: influences of mean environmen- 

 tal conditions on their vulnerability to surface fishing gear. 

 Mar. Fish. Rev. 43(6):1-11. 

 HoTTS, H., AND T. Ogawa. 



1955. On the stomach contents of the skipjack, Katsuwomis 

 pelamis. Bull. Tohoku Reg. Fish. Res. Lab. 4:62-82. 



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