SKIPJACK TUNA, KATSUWONUS PELAMIS, HABITAT 

 BASED ON TEMPERATURE AND OXYGEN REQUIREMENTS 



Richard A. Barkley,' William H. Neill,^ and Reginald M. Gooding^ 



ABSTRACT 



The habitat of skipjack tuna, Katsuwonus pelamis, has generally been assumed to be the warm surface 

 layers of tropical and subtropical ocean, where most of these fish are seen and caught. But experiments 

 with captive Hawaiian skipjack tuna imply that their habitat is more restricted, with boundaries 

 defined by both temperature and dissolved oxygen. The lower temperature limit appears to be about 

 18° C. The upper temperature limit apparently varies with size of the fish, from 30° C or more for small 

 individuals to as little as 20° C for the largest. Skipjack tuna also require water with unusually high 

 concentrations of dissolved oxygen, at least 3.0-3.5 ml/1 (4-5 ppm), for long-term survival. If our 

 Laboratory findings with captive skipjack tuna accurately define their natural habitat, only the 

 smallest of these animals can inhabit the warm surface waters of the tropics; those larger than 4-5 kg 

 must inhabit the thermocline. Our hypothesis, which can be tested, explains many features of the 

 known distribution of skipjack tuna in the eastern and central Pacific Ocean. 



For skipjack tuna, Katsawonus pelamis (Lin- 

 naeus), the question "Where are the fish?" is par- 

 ticularly hard to answer. Their habitat is known 

 only in the most general terms. These fish are 

 found in tropical and subtropical waters of all 

 oceans, at surface temperatures between 15° and 

 30' C. Because they are caught most frequently by 

 methods such as trolling, purse seining, and pole- 

 and-line fishing, it is generally assumed that skip- 

 jack tuna inhabit the surface mixed layer. 

 Japanese longline gear, which fishes well below 

 the sea surface, catches very few skipjack tuna, 

 and then only on the hooks which fish nearest the 

 surface ( Yabe et al. 1963). In a review of the litera- 

 ture on this species, Matsumoto and Skillman^ 

 pointed out that the sea-surface temperature 

 range where most skipjack tuna are caught varies 

 from one fishery to another. Off Tasmania and 

 southeast Australia, the range is 15° to 18° C. Off 

 Japan and South America, the range appears to be 

 20° to 24° C, while the fishery off southern India 

 operates in water of 28° to 29° C. The Hawaii fleet 

 fishes skipjack tuna all year, in water with surface 



'Southwest Fisheries Center Honolulu Laboratory, National 

 Marine Fisheries Service, NOAA. P.O. Box 3830, Honolulu, HI 

 96812. 



^Southwest Fisheries Center Honolulu Laboratory, National 

 Marine Fisheries Service, NOAA, Honolulu, Hawaii; present 

 address: Department of Wildlife and Fisheries Sciences, Texas 

 A&M University, College Station, TX 77843. 



^Matsumoto, W. M., and R. A. Skillman. SjTiopsis of biological 

 data on skipjack tuna, Katsuwonus pelamis (Linnaeus). Man- 

 user, in prep. Southwest Fish. Cent. Honolulu Lab., Natl. Mar. 

 Fish. Serv., NOAA, P.O. Box 3830, Honolulu, HI 96812. 



temperatures ranging from 23° to 27° C, with the 

 majority of catches in the warm, summer months. 



Because studies of the occurrence of wild skip- 

 jack tuna in relation to sea-surface temperature 

 yield such disparate results from one area to 

 another, and because the total temperature range, 

 15° to 30 ° C, includes more than half of the surface 

 area of the world's oceans, we have worked with 

 captive animals in a series of experiments in- 

 tended to define more precisely their physiological 

 requirements. Results of three of these studies 

 (Neill et al. 1976; Dizon et al. 1977; Gooding and 

 NeilH) provided information on the skipjack tu- 

 na's temperature and dissolved oxygen require- 

 ments which, taken together, appear to define the 

 actual habitat of this species in nature. 



We present here a summary of the physiological 

 studies and their results, which suggest specific 

 temperature and dissolved oxygen values that 

 define the spatial limits of the skipjack tuna 

 habitat. With the resultant temperature and dis- 

 solved oxygen values, we have mapped the habitat 

 of the skipjack tuna using averaged oceanographic 

 data from the eastern Pacific Ocean. 



These habitat maps present our hypothesis in a 

 testable form. If skipjack tuna in nature have the 

 same requirements as those studied in captivity, 

 their distribution should, on average, correspond 



''Gooding, R. M., and W. H. Neill. Respiration rates and low 

 oxygen tolerance limits in skipjack tuna, Katsuwonus pelamis. 

 Manuscr. in prep. Southwest Fish. Cent. Honolulu Lab., Natl. 

 Mar. Fish. Serv., NOAA, P.O. Box 3830, Honolulu, HI 96812. 



Manuscript accepted February 1978. 

 FI.SHERY BLLLETIN: V0L."76, NO. 3. 1978. 



653 



