X 



the daylight hours. Summaries of these obser- 

 vations are presented in tables 19 to 23. 



Longline Fishing 



During four of the cruises, 25 longline 

 stations were occupied. No longlining was under- 

 takenduring Charles H. Gilbert cruise 45. The 

 longline gear used was a modification of the 11- 

 hook basket described by Mann (1955), alterna- 

 ting floatline lengths of 10, 5, and fathoms (in 

 the last case the mainline was tied directly to 

 the buoy) instead of the usual 10 -fathom length. 

 Positions and species composition of the catch 

 are presented in table 24. Common and scien- 

 tific names of fish caught are listed in table 27. 



Surface Trolling 



Two lines were trolled during daylight 

 hours. A summary of surface trolling results 

 for the five cruises is presented in table 25. 



Tagging 



A total of 236 skipjack were tagged with 

 the all - plastic dart -type tags described by 

 Yamashita and Waldron (1958). A summary of 

 skipjack tagging results is presented in table 26. 



LABORATORY PROCEDURES 



Salinity Determination 



The surface salinity samples obtained 

 at each bathythermograph lowering were ana- 

 lyzed on shipboard using a modification of the 

 Knudsen method ( Van Landingham, 1957). A 

 comparison of the shipboard and the subsequent 

 laboratory determinations showed no significant 

 difference between the two. The salinity data 

 are incorporated in tables 2 to 6. 



Phosphate Determination 



Surface phosphate samples were collect- 

 ed on Hugh M. Smith cruises 50 and 51 and on 

 Charles H. Gilbert cruises 44 and 46. These 

 samples were analyzed by the hydrazine sul - 

 phate modification of Deniges' method (King, 

 Austin, and Doty, 1957). The results are in 

 tables 2, 3, 4, and 6. 



longest dimension, plus the nonfood—' organisms 

 2-5 cm. in longest dimension, were removed 

 from the sample and not included in the weight 

 or group count data. 



2. The weights of plankton expressed 

 in g. /I, 000 m. 3 (tables 13-17) were converted 

 from volumetric displacement values for Hugh M. 

 Smith cruises 50 and 51 and Charles H. Gilbert 

 cruise 44. No significant difference was found 

 between plankton volumes determined by volu- 

 metric displacement and those weighed directly 

 after draining in a 56XXX grit gauze sock. This 

 conclusion is based on a regression analysis in 

 which 63 plankton samples ranging in displace- 

 ment volume from less than 5 cc. to more than 

 200 cc. were drained, weighed, and volumetri- 

 cally measured by water displacement. The 

 regression equation of weight on volume was 

 Y= 0.9954X. The deviationfrom a theoretical 

 one-to-one basis was 0. 0046 (E. C. Jones , 

 personal communication). 



Five stations from each cruise, except 

 Hugh M. Smith cruise 50, were selected for 

 group-count analysis (phylum to order) follow- 

 ing the method described by Jones (McGary, 

 Jones, and Austin, 1956). For Hugh M. Smith 

 cruise 50, six stations were analyzed. The 

 stations chosen were situated in one of three 

 water types characterized by comparatively 

 high salinity (> 34.9 °/oo), intermediate salinity 

 (34.5-34.9 °/oo). or low salinity (< 34.5 °/oo). 

 The group composition and the percentage - 

 occurrence of each group are presented in 

 table 18. 



Zooplankton 



For all cruises, the methods for deter- 

 mining zooplankton abundance and composition 

 described by King and Hida (1957) were followed 

 with two exceptions: 



1. All organisms above 5 cm. in 



2/ Siphonophores , medusae, ctenophores, 

 heteropods, and tunicates, as described by 

 King and Hida (1957). 



