and strayed from their position dircctl.v beneath 

 the log. 



When the fish were undisturbed, the conical dis- 

 tribution beneath the log was not apparent, owing 

 to movements in the horizontal plane and the break- 

 ing up of groups. The mixed school of C. cabalhis, 

 C. hippos, C. marginatus, Elagatis bipinnvlatus, and 

 Psenes pacificus broke up into smaller units, and 

 these at times moved at least 15 m. away from the 

 object. Juvenile kyphosids swam 1.5 to 3 m. away 

 from the object but did not range as far as the 

 juvenile carangids. Adult Canthidermis maculatus 

 frequently swam beyond the limit of visibility — 

 15 m. — and returned to the object. Abudefdiif saxa- 

 tilis and Blenniolus brevipinnis, on the other hand, 

 always remained near the object. 



The relative vertical position of species usually 

 was maintained under both disturbed and undis- 

 turbed conditions. Those species that increased 

 their horizontal range when undistiu'bed also in- 

 creased, to a lesser extent, their vertical range of 

 movements. The juvenile kyphosids swam as deep 

 as 1.5 m. below the object; Pseudupetjcus, Decaptcrus, 

 and Selar were observed at a depth of 12 m. (limit 

 of visibility from the surface). Adult Canthidermis 

 was the only species whose relative vertical position 

 changed markedly. Under disturbed conditions this 

 species was often among those occupying a position 

 close to the object, but after the disturbance had 

 ceased they ranged from the surface to depths over 



12 m. Juvenile Canthidermis, on the other hand, 

 occupied the same relative vertical position under 

 disturbed and undisturbed conditions. 



Commonly the responses of juvenile fish to a drift- 

 ing object differed from those of the adult. Adults 

 swam deeper, ranged farther, and appeared beneath 

 the object less frequently than did juveniles. With 

 the e.xception of adult Sectator and Canthidermis, 

 they did not always respond to movements of the 

 skiff by moving toward the object as did all the 

 juvenile fishes. It was not possible, therefore, to be 

 certain that adult Euthynnus lineatus, Coryphaena 

 hippurus, Caranx cabaUus, or Selar crumenophthalmus 

 were truly associated with a particular object. 



POSITION RELATIVE TO OBJECT AND 

 LATERAL BODY COLORATION 



The lateral coloration of the fishes and their posi- 

 tion relative to the object were correlated. The 

 species that remained closest to the log were darker 

 than were those that maintained greater distances 

 from the object or associated with the object only 

 intermittently (table 7). For example, Abudefduf 

 saxatilis, Psenes pacificus, all species of Caranx, the 

 kyphosids, Blenniolus brevipinnis, and Lobotes paci- 

 ficMS, were yellow, brown, or black and remained 

 near the log. On the other hand, Chromis atrilobata, 

 brownish above, silvery below, occupied a deeper 

 position, and Selar crumenophthalmus and Decap- 

 tcrus sp., which were silvery, regularly occupied the 



Table 7. — Lateral coloration (live), estimated vertical dislribiition and aggregation type of certain species associated unth flotsam 



in the offshore waters of Central America in 1963 



Fishes 1 



Lateral coloration (live) 



Estimated 



vertical 



distance 



from 



object^ 



Grouping 



Juvenile- 



Blenniolus brevipinnis __ 



Abudefduf saialiUs 



Canthidermis maculatus 



Polydactylus approiimans^ 



Kypbosus analogus 



Kyptiosus elegans 



Sectator ocyurus 



Carani caballus 



Caranz liippos.. _ 



Carani marginatus 



Elagatis bipinnulatus 



Seriola sp 



Psenes pacificus 



Chromis atrilobata 



Decapterus sp 



Selar crumenophthalmus 



Pseudupeneus grandisquamis . 



Adult: 



Canthidermis maculatus _ 



Carani caballus 



Dark brown with black bars. ._ 



Yellow with dusky bands 



Blue with white spots to black__ 



Silvery below, blue above 



Black with pale purple stripes and spots 



Black with pale purple stripes and spots 



Yellow with brown stripes below, dark olive green above 



Yellow below, olive above 



Yellow with dark dusky bands 



Yellow with dark dusky bands 



Ycilow with two blue stripes below, dark blucpreen above 



Yeilow with black bands below, dark olive above 



Yellow with brown stripes below, olive above 



Silvery below, pale brown above 



Silvery below, blue above 

 Siivery below, blue above 

 Silvery below, blue above 



Blue with white spots to black 



silvery below, blue above 







0-3 

 3 

 3 



15-150 



150-200 

 150-600 



0-300 

 600-1300 



Pure school 

 Individual 



Mixed school 



Pure school 

 Mixed school 



Pure school 



' Only thoae species are included for whieii we have sufficient notes on vertical distribution. 



2 Estimate made under disturbed conditions. 



3 Did not school beneath log but to one side near the surface. 



FLOTSAM IN OFFSHORE WATERS 



23 



