presented as a function of zooplankton volume for 

 data obtained on SCOT, SCOPE, and EASTROPIC ex- 

 peditions. The SCOT data increase the significance 

 of the relationships previously observed (SCOPE and 

 EASTROPIC) and show that seasonal variations do 

 not alter the relationship. The water-column chloro- 

 phyll a (mg/m") and zooplankton-volume relation- 

 ship is presented in figure 3. Again a significant 

 relationship is obtained and the coefficient of varia- 

 tion is nearly identical in the two cases. These data 

 strengthen our previous belief that the zooplankton is 

 autocthonous and that seasonal variations in the rela- 

 tionship are quite small. 



Figure 4 is a plot of zooplankton volume against 

 nekton volumes obtained at night stations on SCOT 

 Expedition. The zooplankton data, like those in 

 figures 2 and 3, refer to standard oblique meter net 

 hauls with 450 m of wire out and are made available 

 by courtesy of the Inter-American Tropical Tuna 

 Commission. The nekton volumes refer to standard 

 hauls. This relationship is statistically significant. 

 It may be concluded fi'om figures 2-4, for the gen- 

 eral area and season covered by SCOT, that: 



1. The biological events leading to the production of 

 a particular crop of nekton (tuna food) occur in 

 the same locality as tlie crop itself, and 



2. The standing crops at the lower trophic levels 

 are replaced about as fast as they are grazed 

 down by those above. 



Zooplankton Standing Crops Around Islands 

 (M. Blackburn) 



Observations made on SCOT Expedition around 

 Clarion, Clipperton, and Cocos Islands, with the 

 help of Messrs. Klawe and Sund of the Inter- 

 American Tropical Tuna Commission, form a small 

 but interesting addition to the study of zooplankton 

 standing crop gradients around ocean islands. Sta- 

 tions were occupied on opposite sides of each island 

 at a distance of about 11 miles from it and a third 

 station was occupied at a distance of about half a 

 mile from the island; each set of stations was occu- 

 pied in the daylight and again at night. Catches made 

 in oblique haids of nets are not altogether compara- 

 ble because the inshore hauls had to be made at shal- 

 lower depths, but catches from surface horizontal 

 tows, which show similar trends, are comparable. 

 The results of surface tows, in displacement vol- 

 umes (ml/lOOOm^), may be summarized as follows; 



arrowheads indicate apparent gradients of increasing 

 crop away from the Island (Clarion) or towards it 

 (Clipperton, Cocos). 



CLARION ISLAND 



Day 



Night 



12 -f- 



37 1- 



- 4 

 19 



10 

 36 



CLIPPERTON ISLAND 



Day 50 >- 85 -* 15 



Night 173 >- 188 -< 55 



COCOS ISLAND 



Day 58 •- 152 -« 70 



Night 138 »- 210 -< 95 



Oceanographlc Survey of Gulf of Tehuantepec 

 (Al Blackburn) 



The period May 27 - June 2 of SCOT Expedition was 

 devoted to a survey of the Gulf of Tehuantepec in 

 southern Mexico, an area in which yellowfln tuna ag- 

 gregate in winter and spring. This area has been 

 selected for intensive study, by means of cruises and 

 moored stations, over a one-year period; the only 

 previous organized oceanographlc work was for a few 

 days in December 1955, during EASTROPIC Expe- 

 dition. It is frequently disturbed by offshore (trans- 

 isthmian) winds during the fishing season, which 

 suggests both the feasibility and the practical need of 

 some system of forecasting tuna distribution from 

 wind conditions. Other interesting features of the 

 area are that it is in the warmest part of the eastern 

 Pacific and a poor area for skipjack tuna. 



The Eastropic observations indicated the presence of 

 a thermal dome, with thermocline top at 10 m below 

 the surface at about 15°10'N, 95°30'W. The SCOT 

 hydrocast and BT data revealed the presence of a 

 thermal ridge with axis along 95°W between about 

 14°30' and 15°50'N, with tiiermocline top at about 

 20 m. To the west of the ridge the thermocline fell 

 sharply by some 50 m into a hollow at about 96°30', 

 beyond which it rose in a rather ill-defined way. Iso- 

 pleths of salinity, thermosteric anomaly, oxygen, and 

 inorganic phosphorus showed the same trends as the 

 isotherms. Surface temperatures, which over much 



