ASSOCIATION OF FISHES WITH FLOTSAM IN THE 

 OFFSHORE WATERS OF CENTRAL AMERICA 



By John R. Hunter, Fishery Biologist (Research), and Charles T. Mitchell Fishery Aid 

 Bureau of Commercial Fisheries Tuna Resources Laboratory, La Jolla, Calif. 92038 



During April, May, June, and October, 1963, a total 

 of 70 purse seine collections were made of the fishes 

 associated with floating objects. Nearly all of these 

 collections were from the offshore waters of Costa Rica. 

 Twelve families of fishes (Lobotidae, Carangidae, Cory- 

 phaenidae, Mullidae, Kyphosidae, Pomacentridae, 

 Scombridae, Blenniidae, Stromateidae, Mugilidae, 

 Polynemidae, and Balistidae) and 32 species were repre- 

 sented in the collections. Most of the species were 

 present during both spring and fall, and nearly all of 

 the fishes were juveniles. 



Nine of the 32 species, including the 2 most abundant 

 ones, Caranx caballus Giinther and Selar crumenoph- 

 thalmus (Bloch), were carangids. The lengths of two 

 species, Abudefduf saxatilis (Linnaeus) and Seriola sp. 

 were greater the farther an object was located from 

 shore. Some species such as C. caballus. Psenes paci- 

 ficus Meek and Hildebrand, and Canthidermis macu- 

 latus (Bloch) were present in almost a complete series 

 of juvenile stages; others as Chromis atrilobata Gill, 



ABSTRACT 



Pseudupeneus grandisquatnis (Gill), and Agonostomus 

 monticola (Bancroft) were represented by only a single 

 juvenile stage. More fishes were collected under large 

 objects than under small objects. The total number 

 of individuals present near moored objects after 5 days 

 did not differ from the numbers present after 20 or more 

 days. The coloration of fishes was related to their as- 

 sociation behavior. Silvery colored fishes did not re- 

 main as close to the object as did the more darkly 

 colored species. Most adult fishes, which did not re- 

 main as near the object as did juveniles, appeared 

 beneath an object only intermittently. Canthidermis 

 maculatus, however, maintained close contact with 

 drifting objects both as adults and juveniles. 



Observations of the behavior of species are discussed 

 in relation to the mechanisms for the association of 

 fish with flotsam that have been postulated by other 

 authors. None of their hypotheses was supported by 

 our data. Additional mechanisms were postulated. 



The association of fishes with floating objects has 

 been exploited by a number of fislieries. .Japanese 

 pole-and-line fisheries and American purse seine and 

 Hve-bait fisheries take advantage of the association 

 of yellowfin tuna, Thunnus albacarcs (Bonnaterre), 

 and oceanic skipjack, Katmwonus prlamis (Lm- 

 naeus), with algae, logs, and other flotsam (Uda, 

 1933; McXeely, 1901). Uda and Tsukushi (1934), 

 and Yabe and Mori (1950) reported that log-asso- 

 ciated schools of tuna provide a consistently higher 

 yield per unit fishing effort than unassociated schools. 



Moored rafts of bamboo or palm fronds are used 

 to attract dolphin-fish, Coryphaena htppurus (Lin- 

 naeus), in seine fislieries of Japan (Kojima, 1955, 



1956, 1960a, 1960b, and 1961). Moored cork-slabs 

 serve the same purpose for Maltese fishermen (Galea, 

 1961). Two types of palm-frond rafts are used by 

 Indonesian fishermen to attract various clupeids, 

 scombrids, Decapkrus spp., and other carangids 

 (Hardenberg, 1950; Soemarto, 1960). In addition 

 to these commercially important species, many 

 others of lesser or no commercial value are also 

 encountered (Murray and Hjort (1912), Yabe and 

 Mori (1950), Uchida and Shojima (1958), Besednov 

 (1900), Kojima (1960a), Mansueti (1963), and 

 Gooding and Magnuson'). 



Note; Approved for piiblication Marrti 8, 196fi. 



' ReRinald M. Gooding and John J. Magnuson — C)baervations on the 

 ecology and beha\ ior of fishes around a drifting raft near Hawaii during the 

 first 48 hours adrift. Manuscript. Bureau of Commercial Fisheries Bio- 

 logical Laboratory, Honolulu, Hawaii. 



FISHERY bulletin: VOLUME 66, NO. 1 



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