FISHERY BULLETIN: VOL. 85, NO. 1 



Loop Current-influenced stations with the 36 south- 

 ern (SE) Loop Current samples showed that the 

 samples were comparable in diel and vertical depth 

 coverage and that species composition was also 

 similar. However, the number of specimens collected 

 at the NE sites were almost 2.5 times that of the 

 SE total. This apparent impoverishment of mycto- 

 phids in Loop Current waters is supported by the 

 data of other workers showing low biomass of zoo- 

 plankton in the Loop Current (Austin 1971; Jones 

 1973). 



Tropical-Subtropical Myctophid 

 Faunal Structure 



The only other work which has extensively ana- 

 lyzed the myctophid assemblage in a tropical-sub- 

 tropical setting is that of Clarke (1973) in the waters 

 off Hawaii (lat. 21 °N, long. 158°W). Estimates of 

 micronekton standing stock off Hawaii (Maynard et 

 al. 1975) and in the eastern Gulf (Hopkins and Lan- 

 craft 1984) show that both ecosystems are oligo- 

 trophic with roughly equivalent micronekton 

 biomass in the upper 1,000 m. Because of these 

 similarities, a direct comparison between the pres- 

 ent study and the findings of Clarke (1973) is 

 possible. 



High diversity was apparent in both myctophid 

 assemblages, with 18 genera, 47 species off Hawaii 

 (Clarke 1973) and 17 genera, 49 species in the east- 

 ern Gulf. Of these taxa, the two systems shared 21 

 species. Excluding 2 bathypelagic species and 2 

 species of uncertain affiliation, 10 species are 

 tropical-subtropical, 5 are tropical and 2 are tropical- 

 semisubtropical according to Backus et al. (1977). 

 Of the seven numerically dominant species of both 

 studies, three {Benthosema suborbitale, Cerato- 

 scopelus warmingii, Notolychnus valdiviae) are 

 shared (Table 9). In fact, C. warmingii is the top 



ranked species on both lists. The other dominants 

 on Clarke's list are Pacific congeners of Atlantic- 

 Caribbean species, or are in very closely related 

 genera (Paxton 1972). The percent of the total num- 

 ber of individuals that the top seven species com- 

 prise is strikingly similar (75.5%, Hawaii, 74.7% 

 Gulf). Considering the difference in gear types and 

 sampling strategy, estimates of numbers of individ- 

 uals for the three shared species also agree well. 

 Clarke's (1973) abundance ranges for B. suborbitale 

 during warm months was 14 to 23 x 10^ m^, com- 

 pared with 32 to 42 in the Gulf; C. warmingii ; 55 

 to 155 vs. 86 to 287; N. valdiviae; 23 to 104 vs. 27 

 to 128. Thus, the contribution of the abundant 

 species in the myctophid faunas appears to remain 

 relatively constant. 



Clarke's (1973) data on diel distributions of B. 

 suborbitale, C. warmingii, and N. valdiviae are also 

 similar to our own. Some differences, which may be 

 the result of localized environmental variations, in- 

 clude shallower MDO's, depression of MDO and 

 zones of abundance during full moon and roughly 

 equivalent day-night abundances off Hawaii. Addi- 

 tionally, members of the Hawaiian A^. valdiviae 

 population were found to have a significant non- 

 migratory fraction, which has not been observed in 

 the Gulf population. Clarke (1973) did note, however, 

 that during several collection periods (March and 

 June) no evidence of nonmigration was observed in 

 Notolychnus. 



Comparison of our species list with those compiled 

 from other studies encompassing tropical-sub- 

 tropical latitudes (Nafpaktitis and Nafpaktitis 1969, 

 Indian Ocean; Hulley 1972, SW Indian Ocean; 

 Clarke 1973, central Pacific; Wisner 1976, eastern 

 Pacific; Hulley 1981, eastern and South Atlantic) 

 showed that 10 myctophid species (8 mesopelagic, 

 2 bathypelagic) were common to all regions and that 

 three {Benthosema suborbitale, Ceratoscopelus war- 



Table 9.— Comparison of the top seven myctophid species and their percentage composition for the 

 tropical-subtropical community off Hawaii (from Clarke, 1973) and the eastern Gulf of Mexico (the pres- 

 ent study). Underline indicates shared species. 



96 



