FISHERY BULLETIN: VOL. 72, NO. 4 



Figure 13. — Locality records and nighttime abundance of Nematoscelis microps adults in the Indian Ocean: a - NE Monsoon period. 



clearly understood. However, lat. 35°-45°N, cor- 

 responding to the North Pacific transition, seems 

 to be the extent of the region in the North Atlantic 

 where N. megalops (instead of N. difficilis ) is the 

 most common Nematoscelis. Nematoscelis atlan- 

 tica, N. microps, and N. tenella also appear in the 

 transition zone of the North Atlantic but not in the 

 corresponding zone in the North Pacific. The 

 northeasterly North Atlantic Current carries 

 warmwater species farther north into the transi- 

 tion zone or even beyond to the subarctic subre- 

 gion. For example, the present survey recorded N. 

 atlantica from lat. 52°N {Atlantis II -9, station 

 371). Outside of its main zone in the North Atlan- 

 tic, N. megalops occasionally occurs in the 

 subtropical and subarctic subregions. It is also the 

 most common Nematoscelis species of the circum- 

 polar transitional regions of the Southern Hemi- 

 sphere, while A^. atlantica, N. microps, and N. 



tenella also were occasionally caught there, from 

 the Indian Ocean sector. 



The eastern tropical Pacific Ocean is considered 

 a subregion of the warmwater zone because of its 

 characteristic hydrographical and faunal proper- 

 ties. Nematoscelis gracilis old form is part of that 

 faunal assemblage. The Indo-West Pacific and 

 eastern tropical Pacific subregions were consid- 

 ered separate from the Atlantic tropical subre- 

 gion (Ekman, 1953). The distribution ofN. gracilis 

 and A^. atlantica presents evidence for this. 

 Nematoscelis microps and A^. tenella are warmwa- 

 ter species, occupying both tropical and subtropi- 

 cal regions (Table 3). Many warmwater plank- 

 tonic species are restricted to tropical latitudes, 

 whereas others are found only outside of this re- 

 gion (examples in Bieri, 1959; Brinton, 1962; 

 Alvarino, 1965; Baker, 1965; McGowan, 1971). In 

 this respect N. gracilis is tropical and N. atlantica 



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