Table 2. — Ecnhgiral characters of the 15 most frequently captured species collected beneath flotsam in the offshore waters of Central 



America in 1963^ 



' Tlie total number of collections was 70. 



~ The total niunber of collections in wliich the species occurred. 



3 Rank based on figures in adjacent columns- t ■ j- ■ i i 



< The number of samples in which a particular species or a Kroui) including this species comprised 50 percent or more of the total number of individuals 

 in a Given collection, 



= RaUKc of the numbers of individuals per collection in which species was found. 

 ^ Median of the numbers of individuals per collection in wiiich species was found. 



T.\BLE 3. — Frequency, abundance, and dominance of spenVs 

 occurring in 10 or fewer collections made in the offshore waters 

 of Central America in 1963. Listed in order of frequency 



Species 



Agnvonfom tat iiwnficola 



PoJijiimii/l'is a I'proximavs 



Kt/phnfin^ ibiiainf 



Alirqil rlijcma 



Bali.tfps itttliilepis 



Kitphnsns tiiinlofiiis 



Lohotes pnciftcii^ 



Seriola colhuriii 



Coriitihaeiid ti'tppurus 



CoTliptlaeim cquisetis 



Kiipbosus sp 



Pofrjdach/lits opercularis.. 



All. r is ttiazard. 



Eiilhi/nuits lineatus..', 



Aliilera motioceros 



Atiitera scripfa 



Frequency 



in 



9 

 8 

 5 

 5 

 3 

 3 

 2 

 2 

 2 

 2 



Abundance' 



(I-ll) 

 (1-12) 

 (1-12) 



(1-2) 



(1-1) 

 (1) 

 (1) 



(2-3) 

 (I) 



(2-3) 

 (1) 

 (1) 

 (1) 

 (1) 

 (I) 

 (1) 



Dominance 



1 Ficures in parentheses show range in number of individuals per collec- 

 tion of occurrence. 



Nine of the 32 species were carangids, and all but 

 1 of these, Scriola colhurni, were among the 15 mo.st 

 frequent species. The carangid, C. cabaUus was by 

 far the most frequent, abundant, and dominant 

 species collected. This fish contributed oO percent 

 or more of the individuals in more than half of the 

 collections. Selar crumcnophthalnius, also a caran- 

 gid, ranked second in frequency, abundance, and 

 dominance. Xo other family «as represented as 

 frequently in the collections. The family Kyphosi- 

 dae was represented by four species but only one, 

 Sedator ocyurus, occurred in more than 10 collections. 



On the basis of their rank by frequency, abun- 

 dance, and dominance, the 15 most frequent species 

 can be divided into three groups: (1) species that 

 occupied about the same rank in all three categories; 



(2) species that were captured frecjuentlj' but were 

 not abundant in the collections in which they oc- 

 curred ; and (3) species captured less freciuently that 

 were abundant in the collections in which thej' oc- 

 curred. The three highest ranking species, C. 

 caballns, Selar crtmicnophthalmiis, and Pscnes paci- 

 ficus were in the first group. Ahiidcfduf saxatilis 

 and Blenniolus hrevipinnis exemplify the second 

 group, and Chronu's atn'Iobatn and Canthidermis ma- 

 cidatiis the third. 



The factors responsible for the tlifferences in fre- 

 ciuenc.v and abundance of species are unknown. 

 For some species, evidence suggested that schooling 

 was a significant factor. All of the 15 most fre- 

 quently captured species, except Abudcfduf and 

 Blenniolus, schooled either with their own or other 

 species beneath flotsam. Abudefduf remained near 

 the object and appeare(.l to defend small territories; 

 Blenniolus maintained contact with the surface of 

 the object and were not aggregated. Possibly the 

 solitary or individual habits of these species were 

 responsible for their lower abundance. Juvenile 

 Chromis school at the stage at which they associate 

 with flotsam. This species was dominant in seven 

 of eight collections made in the same area on the 

 same day. The median number of individuals in 

 these seven collections was 199. Chromis was domi- 

 nant only once in the remainder of the collections, 

 and the median number of fish per collection was 

 two. The irregular abundance of Chromis could 

 be ascribed to a tendency toward the recruitment 

 of an entire school. 



FLOTSAM IN OFFSHORE WATERS 



19 



