PHYSICAL, CHEMICAL, AND BIOLOGICAL OBSERVATIONS 



IN THE EASTERN TROPICAL PACIFIC OCEAN 



SCOT EXPEDITION, APRIL-JUNE 1958 



SCOT (Scripps Cooperative Oceanography and Tuna) 

 Expedition, carried out between 23 April and 20 June 

 1958, in eastern tropical Pacific waters, was a co- 

 operative venture utilizing funds and personnel of the 

 Scripps Institution of Oceanography (Tuna Oceanogra- 

 phy Research Project) and the Inter-Ainerican Trop- 

 ical Tuna Commission. The reference number of the 

 cruise for Scripps Institution purposes is TO-58-1. 

 Funds for the Scripps Institution group were provided 

 by the U. S. Bureau of Commercial Fisheries under 

 Department of Interior Contract 14-19-008-9354. 

 The Scripps research vessel Spencer F. Baird , 

 Captain A. W. Phinney commanding, was employed. 

 The main objectives of the expedition were: 



a. to augment our knowledge of the seasonal and 

 regional variations in primary production and 

 standing crops of phytoplanidon, zooplankton, 

 and nekton, and their relationships to tuna 

 abundance and to the physicochemical environ- 

 ment in areas of interest to the Ainerican tuna 

 fisheries; 



b. to study the abundance and distribution of tuna 

 eggs and larvae in waters west of the Mexican 

 mainland north of 17°N latitude; 



c. to study the physical, chemical, and biological 

 features common to oceanic "fronts" in the 

 vicinity of southern Baja California. 



The Scripps Tuna Oceanography Research (STOR) 

 group was primarily concerned with objective (a). 

 The expedition data, together with similar informa- 

 tion gathered on previous and subsequent investiga- 

 tions will provide the basis for an evaluation of the 

 biological events in the ocean environment with spe- 

 cial reference to the distribution and behavior of 

 tunas. 



Objectives (b) and (c) were of particular interest to 

 scientists of the Inter-American Tropical Tuna 

 Commission since such work forms an integral part 

 of their continuing field research program. 



It was originally intended that the latter portion of tlie 

 expedition (Acapulco-San Diego) would be carried out 

 under the leadership of Dr. Bell M. Shimada of the 

 Inter-American Tropical Tuna Commission, and de- 

 voted mainly to the Commission's objectives. Unfor- 

 tunately, the death of Dr. Shimada and his colleague, 



Mr. Townsend Cromwell, en route to join the expedi- 

 tion, prevented the complete fulfillment of these 

 objectives. Objective (c) was abandoned. 

 Dr. Maurice Blackburn, STOR Pi'oject Leader, took 

 charge of the work and attained objective (b) before 

 returning to San Diego. 



Figure 1 shows the expedition track. 



The following is a list of scientific personnel who 

 participated in the expedition: 



**Mr. Carl M. Boyd, Research Assistant, Scripps 

 Institution 



Dr. Maurice Blackburn, Associate Research Biol- 

 ogist, Scripps Institution (Expedition Leader, 

 Acapulco-San Diego) 



*Mr. Donald E. HoUingshead, Laboratory Techni- 

 cian, Scripps Institution 



*Mr. Robert W. Holmes, Assistant Research Biol- 

 ogist, Scripps Institution (Expedition Leader, 

 San Diego-Acapulco) 



Mr. Witold L. Klawe, Scientist, Tuna Commission 



Mr. John M. Jaynes, Marine Technician, Scripps 

 Institution 



Mr. Robert J. Linn, Senior Marine Technician, 

 Scripps Institution 



Mr. A. Dougall Reith, Senior Marine Technician 

 Scripps Institution 



*Mr. Alan C. Smith, Marine Technician, Tuna 

 Commission 



Mr. Paul N. Sund, Scientist, Tuna Commission 

 ♦Dr. William H. Thomas, Assistant Research Biol- 

 ogist, Scripps Institution 



* San Diego-Acapulco 

 ** Acapulco- San Diego 



SUMMARY OF PRELIMINARY RESULTS 



While most of the data obtained on SCOT have not yet 

 been examined in detail, certain of the biological re- 

 lationships have been examined cursorily and are 

 presented below to illustrate some of the types of re- 

 lationships that are being e.xamined. More detailed 

 and rigorous expositions will appear elsewhere. 



Interrelationships of Standing Crops - Phytoplankton , 

 Zooplanlrton , and Nekton (R. W. Holmes and 

 M. Blackburn) 



In figure 2 surface chlorophyll a_ concentration is 



