Investigations, now standard also in investiga- 

 tions by the Scripps Institution and Inter- 

 American Tropical Tuna Commission in the 

 eastern tropical Pacific; the main body of the 

 net is made of 30XXX nylon grit gauze, the 

 rear section and detachable cod end of 56XXX 

 nylon grit gauze. 



Oblique hauls with this net were made usually 

 through the upper 300 m. of water, by paying 

 out the net on 450 m. of wire at 50 m./min. 

 and retrieving it at 20 m./min., the ship speed 

 being varied to maintain a wire angle of 45° 

 during the retrieving period. However, on 

 stations 1 to 67 of TO-59-2 an attempt was 

 made to make oblique hauls through the upper 

 140 m. only, by paying out 200 m. of wire 

 instead of 450 m., this being the standard 

 procedure by CalCOFI investigators for the 

 Baja California region; in fact, the net gener- 

 ally did not go as deep as 140 m. because of 

 technical difficulties. The greatest depths 

 actually reached were estimated for all hauls 

 from wire angles and wire lengths. Horizontal 

 hauls with the nonclosing meter net were all 

 made just below the sea surface. 



The closing Clarke-Bumpus net or sampler 

 was used on TO-59-1 and TO-59-2 to obtain 

 special samples for Paul Sund, of the Inter- 

 American Tropical Tuna Commission, who has 

 kindly made available the data on displacement 

 volumes. The equipment is an enlarged Clarke- 

 Bumpus sampler with mouth diameter 25 cm. ; 

 the body of the net is made of 706 Nitex and 

 the detachable cod end of 316 Nitex. The 

 sampler was lowered, closed, to a desired 

 depth; it was then opened and hauled horizon- 

 tally, then closed and brought to the surface. 

 Routinely, a series of three 15-min. or 30-min. 

 hauls was made at each station where the 

 samplers were used; one haul in the center of 

 the mixed layer, one in the thermocline, 

 and one well below the thermocline. 



The tabulated standardized volumes are 

 given for the total zooplankton (T ) and the small 

 zooplankton (S) of each haul; small zooplankton 

 is total zooplankton with organisms of length 

 > 5 cm. removed. 



Flowmeters were calibrated before and after 

 cruises. 



Micronekton standing crop 



The large zooplankton and small nekton 

 (organisms from 0.5 to 10 cm. long, approxi- 

 mately, for which the term "micronekton" 

 is appropriate) were captured in two different 

 nets. 



One of these nets, described previously 

 by Holmes and Blackburn (1960), was essen- 

 tially a very large coarse-meshed plankton 

 net: about 20 ft. in overall length, mouth 

 opening 5 ft. square, Marion Textiles pattern 

 467 nylon throughout, terminating in a detacha- 

 ble meter-net cod end of 56XXX nylon grit 

 gauze. 



This net was used to make oblique hauls in 

 the upper 90 m. of water at night stations, 

 at a speed of 5 kn. On Expedition SCOT 

 (TO-58-1) the net was used with attached 

 weights (Holmes and Blackburn, 1960). The 

 work on TO-58-2 consisted of experimental 

 hauls (not listed in this report) with stream- 

 lined 45-lb. depressors instead of weights; 

 as a result, the hauling procedure on TO-59-1 

 and TO-59-2 was restandardized for a net 

 used with two depressors to sample the upper 

 90 m. of water, as follows: 350 m. of 3/8-in. 

 wire paid out at 25 m./min. and retrieved at 

 10 m./min., ship speed 5 kn. throughout, total 

 time 49 min. Actual maximum depth was deter- 

 mined by an attached bathythermograph. No 

 flowmeter was used, and the tabulated volumes 

 are displacement volumes of the total catch, 

 minus tunicates, siphonophores, and medusae. 



The other ("high-speed") net was used at the 

 ordinary cruising speed of the ship, which 

 varied between 9 and 10 kn., in the upper 10 m. 

 only, normally for periods of from 2 to 3 hr. 

 when opportunity offered. Hauls on TO-58-2 

 and TO-59-1 were experimental and have not 

 been listed; those on TO-59-2 were made 

 routinely and have been listed in table 6. The 

 net is conical, of mouth diameter 70 cm., about 

 8-1/2 ft. in overall length, Marion Textiles 

 pattern 467 nylon throughout, terminating in a 

 detachable meter-net cod end of 56XXX nylon 

 grit gauze. It was normally towed with 50 m. of 

 3/8-in. wire out, with one streamlined 45-lb. 

 depressor. No flowmeter was used; but iden- 

 tical tows of the complete net with flowmeter 



