deepest position of all the permanently associated 

 fishes. This relationship suggests a protective ad- 

 \antage aflbrded bj' the log other than the physical 

 obstruction of predators. The dark brown, yellow, 

 and black of the closely associated species was well 

 adapted to the colors of the most commonly occur- 

 ring flotsam. Thus, when associated with flotsam, 

 the more darkly colored species were probably less 

 conspicious to predators than when isolated. From 

 examination of fishes associated with flotsam in the 

 Atlantic, Murray and Hjort (1912) made similar 

 speculations. They also suggested that Naucrales 

 dudor, blue with darker transverse bars, might 

 0CCUP3' an intermediate position between the organ- 

 isms strongl.y associated with flotsam and those 

 which merely live near drifting objects. 



Although both Canthidermis macnlatuf; and Pohj- 

 dactijlus approximans had a pelagic coloration, they 

 were frequently near the object when frightened. 

 The fright reaction of Pohjdaclijhi^ differed from that 

 of other species. These fish formed a compact 

 rapitUy moving school a few centimeters below the 

 water surface. The school moved about near the 

 object but never below it. Adult Canthidermis when 

 undisturbed swam deeper and ranged farther from 

 the object than all the yellow, brown, and black 

 species. When frightened they moved to to 3 m. 

 below the object. Thus, this species occupied a 

 position in keeping with its pelagic coloration only 

 under undisturbed conditions. Canthidermis has the 

 ability to turn from the normal pelagic coloration, 

 blue with white spots, to black. Juveniles and 

 adults had intermediate color phases as well as 

 pelagic and dark phases. 



Within the same species, coloration appeared to 

 reflect differences in the behavior of association. 

 The silvery adult C. cabaUus did not maintain close 

 contact with an object and appeared beneath it only 

 intermittently. The yellowish juvenile C. caballus, 

 on the other hand, maintained close contact with the 

 object. Gooding and Magnuson (see footnote 1) 

 reported that when Psenes pacificus was associated 

 with their raft it was yellow, but unassociated indi- 

 viduals were silvery. 



FEEDING BEHAVIOR 



Adult Canthidermis, Alutera, and juvenile Klaqatis 

 frequently were seen feeding on colonial .salps. Once 

 we saw three Canthidermis nipping the base of the 

 neck and legs of a green turtle. On no other occasion 

 did we see this species engaged in activities that 



could be interpreted as parasite cleaning. Occasion- 

 ally juvenile kyphosids were observed snapping at 

 the surface of a log or branch. Juvenile AbudcfduJ 

 showed this behavior more frequently. 



Adult Coryphaena hippnrus frequently pursued 

 smaller fishes locatetl beneath flotsam. We did not 

 see them capture fish, but the stomach of an adult 

 Cortjphaena taken by hook and line contained a 

 Caranx caballus. Frequently fishes with lateral 

 lesions were seen beneath logs. These included 

 Caranx caballus, Canthidermis marulalus, and Elagatis 

 bipinnulatiis. 



Two schools of skipjack, and one of yellowfin tuna 

 were associated with logs in the study area and were 

 seined by American tuna fishermen. When the 

 boats reached port, stomach contents of fish from 

 each school were examined and the lengths of the 

 fish determined. Euphausiids and myctophids were 

 the dominant food organisms in the stomachs of 

 skipjack, and the portunid crab, Portunus affinis, in 

 the stomachs of yellowfin tuna. Only seven stom- 

 achs contained fishes — carangids and scombrids — 

 that may have been associated with flotsam (table 8). 

 Stomachs from each of the three schools contained 

 debris of the kind usually found near drifting logs 

 (pieces of wood, thorns, and bird feathers). 



Table S. — Occurrence of flotsam-associated fishes in the stom- 

 achs oj two schools of oceanic stti-pjactt, and one school of yel- 

 lowfin tuna associated with flotsam in offshore waters of Cen- 

 tral America in W6S 



Stomach content.-* 



Fish 



Flolsara-iissociated 

 species 



fnassociaieij species . 



Iniilcriiiliccl remains- 



InviTlchratcs, 



Bird featliers and 



plant debris_ , 



Skipjack 



seined 



October .•!, \Wii 



(222-48)1 



Number 



Volume 

 Ml. 



n 



281.1 



0.1) 



212.8 



Skipjack 



seined 



October (i, 11163 



(213-61)1 



Yellow flit tuna 



seined 



June 18-22, 1965 



(149-107)' 



Volume 

 Ml. 



77.0 

 1448.5 

 

 25 



Volu me 

 Ml. 



575.0 

 20fi. 

 790.0 

 1579. 



' .\t left, number examined: at rifiht. number with food. 



COURTSHIP BEH.WIOR 



No eggs of any kind were found attached to the 

 flotsam. Some species observed near drifting objects 

 were, however, in repro(lu('tive condition. Three 

 ripe male black skipjack were captured from a 

 school near a large drifting tree. Underwater obser- 

 vations of these fish revealed a high frequency of 

 wobbling and chasing. This behavior was similar 



24 



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