A Raft for Direct Subsurface Observation at Sea 



By 



REGINALD M. GOODING 



Fishery Biologist 



Bureau of Commercial Fisheries 



Biological Laboratory, Honolulu, Hawaii 



ABSTRACT 



A raft with an underwater observation chamber was constructed to allow- 

 close study of the accumulations of fishes around a floating object at sea. A 

 mother vessel carries the raft to the observation site and sets it adrift. The 

 observation chamber accommodates one observer, who has a 360" view of the 

 surrounding water. New information on fish behavior and ecology was gathered 

 during several short drifts near the island of Hawaii and two drifts of 8 and 9 

 days in the equatorial Pacific. 



INTRODUCTION 



In 1962 a raft with an underwater observation 

 chamber was built at the U.S. Fish and Wildlife 

 Service, Bureau of Commercial Fisheries Bio- 

 logical Laboratory in Honolulu to be used to ob- 

 serve ecological and behavioral interactions 

 among fishes which are attracted by drifting ob- 

 jects on the open ocean. 



Pelagic fishes frequently are seen in the vicin- 

 ity of drifting material at sea, and at least three 

 commercial seine fisheries and a pole-and-line 

 fishery take advantage of fish accumulations 

 around anchored floats. Dolphin, Coryphaena 

 hippurus Linnaeus, are netted around anchored 

 bamboo rafts in the Sea of Japan (Kojima, 1956) 

 and around large slabs of cork anchored in the 

 Mediterranean near Malta (Galea, 1961): mack- 

 erel scad, Decapterus sp., are caught around 

 anchored coconut fronds in the Java Sea (Soe- 

 marto, 1960; Natadisastra, 1952; Westenberg, 

 1953). In the Japanese pole-and-line fishery, 

 large catches of skipjack tuna, Katsuwonus pe- 

 lamis (Linnaeus), yellowfin tuna, Thunnus alba- 

 cares (Bonnaterre), and bigeye tuna. Thunnus 

 obesus Lowe, are made near drifting material 

 during certain seasons (Inoue, Amano, and Iwa- 

 saki,1963; Kimura, 1954; Yabe and Mori, 1950). 



Prior to the construction of the raft, several 

 techniques for observing tuna underwater at sea 

 from the research vessel Charles H^. Gilbert 

 were developed at the Bureau's Laboratory in 

 Honolulu. This work culminated with the con- 

 struction of an observation ''blister'" in the bow 

 of the Gilbert (Strasburg and Yuen, 1960). Al- 

 though fishes near floating logs have been seen 

 from the underwater windows, the presence of 

 the vessel so modifies the environment that seri- 

 ous studv has not been practical. Since the raft 

 Nenue^ (fig. 1) served as both the observation 

 platform and the drifting object, it permitted 

 study under conditions as natural as possible. 



DESIGN 



The Nenue consists of three units: a wooden 

 raft buoyed with steel drums, a cylindrical steel 

 observation chamber, and a small deckhouse 

 (fig. 2). 



Senue is the Hawaiian name for a reef fish, 

 Kyphosus cinerascens , which is catsmon under 

 floating objects during its juvenile stage. 



