PHYSICAL, CHEMICAL, AND BIOLOGICAL OBSERVATIONS 



IN THE EASTERN TROPICAL PACIFIC OCEAN: 



THREE CRUISES TO THE GULF OF TEHUANTEPEC, 



1958-59 



by Maurice Blackburn, Raymond C. Griffiths, 

 Robert W. Holmes, and William H. Thomas 



ABSTRACT 



This report lists the results obtained on the following three cruises in the 

 region of the United States tropical tunafishery: TO-58-2, October-December 1958; 

 TO-59-1, January-February 1959; and TO-59-2, August-September 1959. 



The main objective of these cruises was to compare distribution of ocean prop- 

 erties and features in the Gulf of Tehuantepec, on the Pacific coast of southern 

 Mexico, at different seasons of the year; this investigation was begun in May-June 

 1958 on cruise TO-58-1 (Expedition SCOT), results of which have already been 

 reported. Observations were made also off the Pacific coast of southern Baja Cali- 

 fornia, thence across the mouth of the Gulf of California and along the coast of 

 southern Mexico towards the Gulf of Tehuantepec, and between the Gulf of Tehuan- 

 tepec and the thermal anticline off the Costa Rican coast. 



Properties measured or computed on all cruises were: temperature, salinity, 

 density, thermosteric anomaly, dynamic height anomaly, dissolved oxygen concen- 

 tration, inorganic phosphorus concentration, attenuation of diffuse submarine 

 daylight, incident solar radiation, standing crop of chlorophyll a, standing crop of 

 zooplankton, standing crop of micronekton, primary production rate, and surface 

 current direction and velocity (by GEK). 



Data on primary production rate and total phosphorus concentration for cruise 

 TO-58-1 (SCOT) are given in appendices. 



INTRODUCTION 



This report lists physical, chemical, and 

 biological oceanographic measurements made 

 on the second, third, and fourth cruises of the 

 Scripps Tuna Oceanography Research (STOR) 

 program of the Scripps Institution of Oceanog- 

 raphy. The first cruise, known as SCOT 

 Expedition or TO-58-1, was made in April, 

 May, and June, 1958, and has already been 

 reported (Holmes and Blackburn, I960). 



The STOR program, financed by the U.S. Fish 

 and Wildlife Service, Bureau of Commercial 

 Fisheries Contract No. 14-19-008-9354, is 

 concerned with the understanding and predict- 

 ability of changes in the aggregation and dis- 

 persal of yellowfin and skipjack tuna in the part 

 of the eastern tropical Pacific Ocean fished 

 by United States vessels. Part of this work 

 consists at present of detailed, seasonally 

 repetitive oceanographic surveys of known 

 centers of tuna aggregation, one of which is 



