MARQUESAS AREA OCEANOGRAPHIC AND FISHERY DATA, 

 JANUARY-MARCH 1957 



By 



Robert C. Wilson, Fishery Research Biologist 



and 



Murice O. Rinkel, Oceanographer 



Pacific Oceanic Fishery Investigations 



U. S. Fish and Wildlife Service 



Honolulu, T. H. 



This report presents the record of 

 observed data from a survey of that portion of 

 the southeastern Pacific Ocean centered in the 

 Marquesas Islands. It is the second POFI re- 

 port concerning this area; the first (Austin 1957) 

 contains the results fron-i a similar endeavor 

 during August-September 1956. The surveys 

 are part of a progrann undertaken by the Paci- 

 fic Oceanic Fishery Investigations (POFI) to 

 study the tuna resources of the southeastern 

 Pacific. The August-September cruises were 

 also part of a broad-scale coverage of the equa- 

 torial Pacific, designated operation EQUAPAC. 



To make these data rapidly available to 

 other agencies studying the Pacific Ocean, they 

 are presented here without analysis. Descrip- 

 tive and analytical reports will follow. 



Three POFI research vessels were 

 assigned to the survey, each with a different 

 primary mission. The oceanic circulation and 

 productivity of a broad area about the Marque- 

 sas was studied by the Hugh M. Smith . The 

 Charles H. Gilbert obtained a measure of the 

 tuna available to live -bait fishing and surface 

 trolling, while the John R. Manning investigated 

 the availability of deep-swimming tuna to long- 

 line gear. 



The Smith departed Honolulu January 11, 

 1957, and returned March 26, after having oc- 

 cupied the oceanographic stations shown in 

 figure 1. The cruise was interrupted by a 

 breakdown on January 31. Repairs were effec- 

 ted at sea, and the cruise resumed on February 

 24, but with some change in the cruise plan. 



The Gilbert departed Honolulu January 

 11, 1957, and returned March 22, after having 

 conducted surface live -bait tuna fishing and 

 surface trolling in the areas shown in figure 2. 



The Manning departed Honolulu January 

 4, 1957, and returned March 12, after having 

 occupied the longline -fishing stations shown in 

 figure 3. 



FIELD PROCEDURES 



Oceanography and Meteorology 



The Smith occupied 5 7 oceanographic 

 stations (table 1) during the survey period. 

 Nansen bottle casts were made to a depth of 

 1 , 20C meters with 13 bottles per cast. The 

 spacing of the Nansen bottles in the upper 200 

 meters was determined from the temperature 

 characteristics of a bathythermograph trace 

 obtained just before the hydrographic cast. 



Water samples were drawn from each 

 bottle for salinity, oxygen, and inorganic- 

 phosphate determinations. The oxygen deter- 

 nninations were made aboard the vessel by the 

 modified Winkler method. No oxygen samples 

 were taiken during the breakdown period. Ana- 

 lysis of samples for inorganic phosphate were 

 also made aboard by use of the hydrazine - 

 sulphate modification of Denige's method (King 

 et al. 1957) and a model B, Beckmaji spectro-" 

 photometer. Phosphate samples collected dur- 

 ing the breakdown period, on special casts, and 

 at 7 oceanographic stations were frozenfor ana- 

 lysis in the laboratory ashore. All the salinity 

 samples taken during the cruise were analyzed 

 ashore. 



In addition to the regular oceanographic 

 stations, two special 300-meter casts with 8 

 Nansen bottles, spaced according to the vertical 

 temperature characteristics, were made for the 

 purpose of collecting water samples for phyto- 

 plankt on analysis (see fig. 1). On one regular 

 oceanographic station, additional phytoplajikton 

 samples were drawn from bottles at selected 

 depths. All of these samples were shipped to 

 the Institutt for Marin Biologi at Oslo, Norway. 



During the cruise, 275 bathythermograph 

 observations were made from the Smith (table 

 2). Lowerings were made every 6 hours be- 

 tween Honolulu and the Equator. Between 

 oceanographic stations, lowerings were made 

 every 3 hours on the run along the Equator and 



