FISHERY BULLETIN: VOL. 73, NO. 4 



Table l.-Tow data for TEUTHIS-18. 



Tow 

 number 



Local time 



Date Begin 



End 



Number 

 flowmeter 

 revolutions 



180 



181 



182 



183 



184 



185 



186 



187 



188 



189 



190 



191 



192 



193 



194 



195 



196 



197 



198 



199 



200 



201 



202 



203 



204 



9/29 

 9/30 



10/1 



10/2 



1703 



2040 



0235 



0657 



1221 



1912 



0015 



0522 



0716 



0904 



1051 



1236 



1429 



1620 



1758 



1937 



2117 



2257 



0036 



0232 



0421 



0630 



1134 



1856 



2340 



2025 

 0213 

 0408 

 1203 

 1710 

 0002 

 0500 

 0657 

 0851 

 1040 

 1220 

 1408 

 1607 

 1751 

 1928 

 2110 

 2250 

 0029 

 0210 

 0409 

 0554 

 1117 

 1612 

 2330 

 0434 



517,814 

 998,460 

 290,325 

 1,061,855 

 841,941 

 884,407 

 872,342 

 399,056 

 307,434 

 336,306 

 284,953 

 346,136 

 307,172 

 306,759 

 275,434 

 295,355 

 284,199 

 293,163 

 274,276 

 308,441 

 305,249 

 935,456 

 844,093 

 857,374 

 935,631 



0000 



0100 



TIME 

 0200 0300 



OUOO 



TIME 

 2130 2230 



Max. 



depth 



(m) 



1,350 



1,500 



365 



1,160 



1,250 



1,320 



1,350 



390 



400 



400 



400 



500 



405 



410 



400 



400 



395 



440 



415 



420 



400 



1,200 



1,240 



1,310 



1,210 



0500 



° 400 



Figure 2.-Time-depth records for typical tows, depth plotted 

 every 5 min. a. Deep tow, no. 204. b. Shallow tow, no. 196. 



A stepped sampling strategy was adopted. The 

 ship speed was 100 m/min (3.5 knots) for all 

 sampling except during retrieval when the ship 

 was nearly stopped. For the shallow tows, 100 m of 

 cable were let out at 50 m/min every 5 min until 

 1,100 m of cable were out. This placed the trawl at 

 about the 400-m depth. After 5 min at this depth, 



the trawl was retrieved as fast as possible. Total 

 duration of shallow tows was about 1.5 h, that of 

 the retrieval phase about 0.3 h. For deep tows, the 

 first 1,100 m of cable were let out in the same 

 manner as for the shallow tows. Beyond 1,100 m, 

 200 m of cable were let out at 50 m/min every 10 

 min until 3,400 m of cable were out. After 10 min at 

 this depth (about 1,200 m), the trawl was retrieved 

 as fast as possible. Total duration of deep tows was 

 about 5 h; retrieval took about 1 h. The distribution 

 of mean sampling times in each 100-m depth in- 

 terval is shown in Table 2. By inspection, the 

 variability seemed small enough to treat all tows 

 within each type equally. 



Table 2.-Distribution of mean sampling time per tow (minutes) 

 and standard deviation (SD) with depth. 



Shallow 



Deep 



Day 

 (6 tows) 



Night 

 (7 tows) 



Day 

 (4 tows) 



Night 

 (5 tows) 



Sample 



depth 



interval 



(m) 



Mean 



time/ 



tow 



(min) 



Mean 



time/ 



tow 



SD (min) SD 



Mean 

 time/ 

 tow 

 (min) 



SD 



Mean 



time/ 



tow 



(min) 



SD 



401 



501 



601 



701- 



801- 



901- 



1,001- 



1,101. 



1,201- 



1,301- 



1,401- 



500 



600 



700 



800 



900 



1,000 



1,100 



1,200 



1,300 



1,400 



1,500 



Total 



291.0 13.7 292.0 23.3 



Sample Processing 



For this study, micronekton was defined as the 

 pelagic marine animals longer than 1 cm caught by 

 the 10- foot I KMT with the trawling methods 

 described above. Each catch was preserved in buf- 

 fered 7% seawater-Formalin. The animals were 

 originally sorted to family or genus but sub- 

 sequently were lumped into larger groups chosen 

 to roughly discriminate between vertical migra- 

 tors and non-migrators, as well as among trophic 

 groups (Table 3). Group names are capitalized in 

 the text. All micronekton except siphonophores 

 were counted, and all groups were weighed (blot- 

 ted wet weight ±0.01 g). Siphonophore biomass 

 was included in the Cnidaria group, but the 



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