GARTNER ET AL.: LANTERNFISHES 



Table 8.— Distribution patterns of eastern Gulf myctophids. NE - northeast, EC - eastern central, SE 



- southeastern. 



'Collections from shallower than 200 m at night. 



are found in our collections. Species with tropical 

 and tropical-subtropical affinities predictably form 

 the largest component of the Gulf myctophid assem- 

 blage during the summer, comprising almost 70% 

 of the 46 species. The seven abundant species all 

 belong to one of these two faunal associations: three 

 (Ceratoscopelus warmingii, Notolychnus valdiviae, 

 Benthosema suborbitale) are tropical-subtropical; the 

 other four {Lepidophanes guentheri, Lampanyctus 

 alatus, Diaphus dumerilii, Myctophum affine) are 

 tropical. Species with subtropical and temperate- 

 subtropical affinities, however, are poorly repre- 

 sented in our collections. A comparison of species 

 number by sampling locale (NE, EC, SE) within the 

 Gulf reveals no particular pattern (Table 8). Ab- 

 sences from an area are probably due to species 

 rarity or inadequate depth coverage of samples 

 rather than to geographic influence. 



Backus et al. (1977) characterized the mesopelagic 

 Gulf of Mexico as a special zoogeographic region 

 because of its unique physical and faunal character- 

 istics. Although our collections captured a larger 

 number of species than did theirs (49 vs. 38), the 

 species composition patterns are very similar (Table 

 8) and indicate that the Gulf myctophid assemblage 

 is overwhelmingly dominated by tropical-subtropical 

 species. However, comparison of the percentage 

 contribution of species within the two collections 

 shows a much different composition (Table 8). 

 Where the data of Backus et al. (1977) showed a 2:1 

 numerical predominance of tropical-subtropical myc- 

 tophids over tropical species, our findings indicate 

 that the two groups are roughly equal. This dis- 

 crepancy may be due to the fact that Backus et al.'s 

 data were based on collections from the western 

 Gulf which has a different circulation pattern and 

 is less directly influenced by the tropical Loop Cur- 

 rent (Jones 1973). Their data were also from collec- 

 tions <200 m at night (J. E. Craddock^") which could 



have affected species number and percentages. 



The largely tropical and tropical-subtropical com- 

 position of the eastern Gulf, during the warmer 

 months at least, is most probably due to the influ- 

 ence of the Loop Current, which may entrain in- 

 dividuals of many uncommon species from the Carib- 

 bean. The size ranges of some of the species taken 

 in our collections support such a hypothesis for tran- 

 sient species. Among the 26 uncommon species, 15 

 are represented only by either newly metamor- 

 phosed through juvenile or juvenile stages (Table 3). 

 This suggests that the large, sexually mature adults 

 may occur and spawn outside the Gulf, with occa- 

 sional transport of eggs, larvae, and juveniles into 

 the Gulf via the Loop Current. Four of the 15 

 species, however, are deep-dwelling Lampanyctus 

 (L. ater, L. cuprarius, L. nobilis, L. tenuiformis) 

 and the sexually mature individuals of these species 

 may be present in the Gulf below our normal fish- 

 ing depths, i.e., >1,000 m. 



Other evidence of Loop Current influence is the 

 relative absence of subtropical species whose geo- 

 graphic distributions usually place them at higher 

 latitudes well to the north or south of the Caribbean 

 Sea and Florida Straits. This is reinforced by the 

 fact that of the six subtropical species we recorded 

 from the Gulf, four {Hygophum reinhardtii, Lam- 

 panyctus ater, L. lineatus, Taaningichthys mini- 

 mus) have uncertain zoogeographic affinities, as 

 they seem to occur often in lower latitudes, including 

 the Caribbean and the Gulf (Backus et al. 1977). 



Although the Loop Current appears to play an im- 

 portant role in the composition of the eastern Gulf 

 myctophid fauna, the biomass transported appears 

 to be low. Comparison of the 25 northern (NE) non- 



'"J. E. Craddock, Woods Hole Oceanographic Institution, Woods 

 Hole, MA 02543, pers. commun. August 1978 (reconfirmed July 

 1986). 



95 



