- 13 



Hauls made with non-closing nets were of three kinds: 

 oblique, surface horizontal, and subsurface horizon- 

 tal. Most oblique hauls were made by lowering the 

 net at 50 m/min until 450 m of wire had been paid out 

 and retrieving at the rate of 20 m/min. The ship 

 speed was varied so as to maintain a wire angle of 

 45° during the retrieving period and the average haul 

 lasted about 32 minutes. Between Acapulco and 

 Tres Marias the majority of oblique net hauls were 

 made by paying out only 200 m of wire: the duration 

 of these hauls averaged about 14 minutes. The depths 

 for individual hauls, estimated from wire angle and 

 wire out, are given among the Station Data in this 

 report, as are the times. The surface (0 m) horizon- 

 tal tow was made astern while the oblique haul was in 

 progress from the starboard side; it is estimated 

 that the net did not sink more than 5 m during any 

 tow of this type. 



The net (about 20 ft in over-all length, of Marion 

 Textiles pattern 467 nylon, throughout) was fastened 

 at the mouth to a 5-ft-square iron frame to which 

 towing bridles and weights were attached to keep it 

 upright in the water when under way; a detachable 

 cod end (as used on the meter nets, 56XXX nylon grit 

 gauze) formed the catching part of the assembly. 



The usual procedure on SCOT, where this net was 

 employed mainly at night stations, was to pay it out 

 on 450 m of 3/8 in. wire at 25 m/min and retrieve it 

 at 10 m/min, all at a ship speed of 5 kt, 63 min in 

 all for the haul. Depth, found for 12 hauls by at- 

 taching a BT, ranged from 72 to 115 m, mean 90 m. 



Data recorded for these hauls consist of starting and 

 finishing times, depth (where measured), and total 

 displacement volume of catch. 



In a few localities (Stations 9, V , 21, 26, 53, 55) 

 where the depth did not permit even the shallow ob- 

 lique haul mentioned above, a subsurface shallow 

 horizontal haul was made. The net was lowered to a 

 depth close to the bottom and towed horizontally. 

 These computed depths ranged from 12 to 63 m. 



Subsurface shallow (10-20 m) horizontal hauls with 

 the same net were made at a few stations (9, 11, 19, 

 21, 53, 55) where the depth did not permit the oblique 

 type of haul described above. 



Night-Light Observations 



The closing net (see Laevitt, Biol. Bull. , 68 and 74, 

 1935 and 1938) was lowered to the desired depth and 

 opened there by lowering a messenger, after which a 

 horizontal haul was made. At the end of the haul, 

 before it was brought to the surface, the net was 

 closed by means of another messenger. 



The catches were preserved in 4 percent buffered 

 formalin. They were later filtered and the total "wet" 

 volumes measured by displacement on shipboard. 

 The volume of water sampled by each haul was de- 

 termined by a method described by the South Pacific 

 Fishery Investigations (now Biological Laboratory, 

 Bureau of Commercial Fisheries, La JoUa), U. S. 

 Fish Wildl. Serv. Spec. Sci. Rep. —Fish. , No. 100, 

 and the displacement volumes were converted into 

 terms of the volume of organisms, in ml, collected 

 from each 1000 m'^ of water strained. The small 

 organisms (see right-hand column, station zooplank- 

 ton tables) are those whose lengths are less than 5 cm. 



Nekton Standing Crop 



The large zooplankton and small nekton (organisms 

 from 0. 5 to 10. cm long, approximately) were cap- 

 tured in what was essentially a very large coarse- 

 meshed plankton net hauled obliquely at about 5 kt. 



At night stations, when weather permitted, an elec- 

 tric light (500 w) was placed above the water from the 

 stern of the drifting vessel. A fine-meshed dipnet 

 was used to capture young tunas and an array of other 

 organisms under the light. Usually the light was left 

 on for about 30 minutes but there were occasional 

 large deviations from that period. 



Bathythermograph Observations 



The list of bathythermograph (BT) obsei-vations has 

 been compiled from information tabulated on BT 

 prints by the Scripps Institution BT Section. It 

 includes: surface temperature; class of temperature- 

 depth trace (C, M, N, or P, according to U. S. Navy 

 Hydrographic Office criteria); and depth of surface 

 layer (SL), defined as depth from surface to top of 

 shai-p negative temperature gradient (or depth of 

 maximum temperature if there is a positive temper- 

 ature gradient). Surface salinity, determined by the 

 Knudsen method, is entered for BT positions at which 

 it was measured. 



Surface Current Velocity and Direction (GEK) 



All measurements were made with neutrally buoyant 

 cable. The conversion from measured electrical 



