MAYNARD ET AL.: HAWAIIAN MESOPELAGIC MICRONEKTON 



Table 3. -Group composition used to sort each catch. 



1. Myctophidae. 



2. Cyclothone (Gonostomatidae). 



3. Other Gonostomatidae. 



4. Sternoptychidae, 



5. Other Stomiatoidei: Astronesthidae, Chauliodontidae, Idia- 

 canthidae, Malacosteidae, Melanostomiatidae, Stomiatidae. 



6. Anguilliformes; Cyemidae, Eurypharyngidae, leptocephali, 

 Nemichthyidae, Serrivomeridae. 



7. Miscellaneous fishes: Alepisauridae, Apogonidae, Bathylagi- 

 dae, Bregmacerotidae, Brotulidae, Ceratioidei, Cetomimidae, 

 Chiasmodontidae, Evermanellldae, Giganturidae, Macrouri- 

 dae, Melamphaeidae, Neoscopelidae, Omosudidae, Opls- 

 thoproctidae, Paralepididae, Scorpaenidae, Trachipteridae, 

 Zeidae, Zoarcidae, larval neritic, unidentified larval mid- 

 water. 



8. Caridea: Opiophoridae, Pandalidae, Pasaphaeidae. 



9. Penaeidae: Penaeidae, Sergestidae. 



10. Euphausiacea: Bentheuphausidae, Euphausiidae. 



11. Mysidacea: Eucopeidae, Lophogastridae. 



12. Miscellaneous Crustacea: Amphipoda, Isopoda, Ostracoda. 



13. Cephalopoda. 



14. Tunicata: Pyrosomidae, Salpidae. 



15. Cnidaria: Hydrozoa, Scyphozoa, SIphonophora. 



16. Miscellaneous invertebrates: Annelida, Cfenophora, Hetero- 

 poda, Pteropoda, Nemertea. 



17. Zooplankton: Copepoda, larval Stomatopoda, other mero- 

 plankton, organisms <, 1 cm, residue. 



Pooled classifications 

 Total fishes = Groups 1-7. 

 Total Crustacea = Groups 8-12. 

 Other invertebrates = Groups 14-16. 

 Total micronekton = Groups 1-16. 



number of siphonophores could not be determined 

 from the assorted zooids (Pugh 1974), and the 

 numerical standing stock of Cnidaria is thus 

 slightly underestimated. Organisms larger than 

 10 g/individual were weighed separately, but their 

 weights and abundance were included in group 

 totals. Most animals with greatest linear dimen- 

 sions of about 1 cm or less, such as the euphausiid 

 Stylocheiron spp., were placed into the zooplank- 

 ton group although some sergestids in this size 

 range were included in Penaeidea. Standing 

 stocks of zooplankton shrimps were calculated 

 from subsamples (Folsom splitter) of one deep 

 tow. 



Calculations 



The volume of water filtered by each tow was 

 determined by multiplying the distance travelled 

 (as determined by the flowmeter) by the area of 

 the net mouth. Mouth areas from 7.08 to 8.19 m^ 

 have been reported for the 10- foot I KMT (Brooks 

 et al. 1974). We used 7.7 m^ for our trawl. 

 Zooplankton biomass was calculated for a mouth 

 area of 7.7 m^ the full IKMT mouth, and 0.785 m^ 

 the area of the cod end mouth. The true zooplank- 

 ton concentration probably lies somewhere 

 between these values because the anterior por- 



tions of the trawl funnel some zooplankton into 

 the cod end while others pass through the meshes 

 (Banse and Semon 1963; Hopkins 1966; Friedl 

 1971). 



To calculate the number of organisms or 

 biomass of each group per 100 m^of ocean surface, 

 the catch was divided by the volume of water 

 filtered; this quotient was multiplied by the 

 maximum depth of the tow and the product was 

 then multiplied by 100. This computation assumes 

 all depths were sampled equally. 



RESULTS 



Standing Stock 



The standing stocks from deep-day and deep- 

 night tows were not significantly different (Ntest, 

 P<0.05) in either number of organisms or biomass 

 for most groups, including total micronekton. Only 

 the numbers of miscellaneous fishes and 

 Mysidacea showed significant diel differences. 

 Likewise there were no significant differences 

 (P<0.05) between the two series of deep tows (tows 

 183-186 vs. 201-204). Consequently we treated all 

 deep tows as replicates and pooled the data to 

 compute mean micronekton standing stocks for 

 the 0- to 1,200-m deep water column (Tables 4, 5). 

 Shallow-day (tows 188-193) and shallow-night 

 (tows 182, 195-200) data were obviously different 

 and were treated separately in these tables. The 

 percentage composition of the fauna by group is 

 illustrated in Figure 3 for each of the three classes 

 of tows. 



The mean standing stocks of total micronekton 

 for the 0- to 1,200-m water column are about 900 

 organisms and 500 g wet weight/ 100 m^ of ocean 

 surface (Tables 4, 5). Fishes comprised over one- 

 half of both the total numbers and biomass; crus- 

 taceans constituted about one-third of the 

 numbers and one-fifth of the biomass, while the 

 cephalopods contributed only one-hundredth of 

 the numbers but one-tenth of the biomass (Tables 

 4, 5). Cijclothone were more than twice as 

 numerous as any of the other 15 groups, totalling 

 almost 35% of the individuals caught (Figure 3a). 

 The distribution of biomass among the groups 

 varied less than the distribution of the abundance. 

 No group contributed more than the Myctophidae 

 which comprised 13% of total biomass (Figure 3a). 

 A comparison of group rank by biomass with rank 

 by abundance indicates that most of the more 



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