PSENES PACIFICUS 

 N-822 



jJBUkiui.^ 



PSEUOUPENEUS GRANOtSOUAMtS 

 N'339 



oi — , — ^Jm^K^L^ , — , 



JO «Q 60 BO 



;-Afi;ANX CABALLUS 

 N'6.ai5 



CHROMIS ATRILOSATA 





H J 160 leO zoo J20 O 20 40 



STANDARD LENGTH 



Milt IMF TFRS 



associated aggregations of fish: (1) frequency— the 

 total number of collections in which a species oc- 

 curred; (2) abundance — the range and median of 

 the numbers of individuals per collection in which 

 the species was found; and (3) dominance— the 

 iiiinibor of samples in which a particular species or 

 a group including this species comprised 50 percent 

 or more of the total number of indi\'i(luals in a given 

 collection. As the structure of the poinilations in 

 the spring was similar to that in the fall, the two 

 series of collections were combined to cak'ulate tiiese 

 statistics. 



Fifteen of the 32 species had freciucncies greater 

 than 10. 'i1ie.se were ranked from 1 to 15 on the 

 basis of their fre(iuency, median abundance, and 

 dominance. Tied \alues were given the average of 

 the ranks (table 2 and fig. 6). The remainder of the 

 species was ranked only by frequency (table 3). 



1'"igi:re 5. — Length frequency for Psenes pacificus, I'scvilii- 

 peneus grandisquamis, Caranx cabaUus, and Chromis atrilo- 

 bata. Numbor.s arc totals for combined spring ami fall 

 collections. 



(table 1). The size range of juveniles of other 

 species was extremely restricted. Chromis alrilohata 

 and Pscudiipcncns grandisquamis had this compact 

 type of size distribution (fig. 5). Other species, not 

 figured, which al.so had a limited size range included 

 Agonoslomus monticoJa, Polijdactylus approximans, 

 and Blcnniolus brevipiiuiis. Pscvduprnrus, Chromis, 

 Agonoslomus, and Polydactylus have pelagic juvenile 

 stages but as adults inhabit other areas. The upper 

 size limit of these species in our collections probably 

 was determined by the size at which they end the 

 pelagic phase of their lives. 



Blcnniolus brevipinnis is a small species; females 

 19.5 mm. long can be se.xually mature (Krejsa, 

 19(i0). Adults and juveniles have been found near 

 drifting logs as well as among rocks and coral heads 

 in inshore areas (Krejsa, IDtiO). Apparently for 

 both adults and juveniles of this species, drifting 

 objects are a suitable pelagic substitute for inshore 

 habitats. 



FREQUENCY, ABUNDANCE, AND 



DOMINANCE OF FISHES 

 COLLECTED BENEATH FLOTSAM 



The characters used by Fager and McCiowan 

 (19G3) for the analysis of zooplankton populations 

 were used to describe the structure of the flotsam- 



FREQUENCY DOMINANCE 



ABUNDANCE 



FBEQUENCY DOMINANCE 



I ABUNDANCE I 

 1 — -H 



FnaiiK G. — Ecological characters of the 15 species most fre- 

 (|Uently captured beneath llot.sam in the offshore waters of 

 Central America in 196:5. Ivicli species was ranked sepa- 

 rately hy.fmiiinicij, the total number of collections in which 

 the species occurred; abundance, median of the numbers of 

 individuals per collection in which the species was found; 

 and dominance, the number of collections in which a specie.s 

 was among those making up 50 percent of tlie individuals. 

 Lines indicate the rank held by each sjiecies in the three 

 rankings. Values upon which ranks wer<' based are shown 

 in each column. In the second column, parentheses enclo.se 

 th(! range of the number of individuals pi'r collection of 

 occurrence. Lor clarity, we separated the 15 species into 2 

 groups: left half of figure, .species who.se ranked abundance 

 was the same as or lower than the ranked frequency; and 

 right half, species whose ranked abundance was higher than 

 the ranked frequency. The total number of collections 

 w.as 70. 



18 



U.S. FI.SH AND WILDLIFE SERVICE 



