Loweina rara (Lütken 1892)

Loweina rara

This lanternfish is moderate in size, growing to about 45 mm and reaching sexual maturity at about 28–32 mm (Nafpaktitis et al., 1977). The largest specimen in the Ocean Acre collections, and the only one in excess of 30 mm, is 41 mm. Presumably, L. rara is a tropical-subtropical species (Backus et al., 1977); it is uncommon throughout its range (Nafpaktitis et al., 1977) and is an “uncommon” lanternfish in the study area. The Ocean Acre collections contain 78 specimens; 50 were caught during the paired seasonal cruises, 29 of these in discrete-depth samples, of which 26 were in noncrepuscular tows.

DEVELOPMENTAL STAGES.—Postlarvae were 8–20 mm, juveniles 21–24 mm, subadults 22–30 mm, and the only adult 41 mm. External sexual dimorphism is obvious soon after transformation; males develop supracaudal luminous tissue and females do not. The adult is a female with ova as large as 0.3 mm in diameter. Of the specimens that could be sexed, 13 were males and 10 were females.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—The reproductive status and life span of L. rara near Bermuda are uncertain. Judging from the numerical dominance of postlarvae (about 70 percent of the total number) and the presence of an adult female in the Ocean Acre collections, L. rara may be an uncommon breeding resident. However, the absence of this species in collections from late November through January, and of specimens 31–40 mm at all times, suggest that few individuals survive long enough to reach sexual maturity.

A prolonged reproductive season for the parent population is apparent in the seasonal distribution of postlarvae, which were taken from March to September, and a summer peak is suggested by the late summer catch when 40 were taken.

VERTICAL DISTRIBUTION.—Daytime vertical range in winter was 801–850 m, in late spring at the surface, and late summer scattered between 251 m and 1150 m. Depth range at night in winter was 101–150 m and 301–350 m, in late spring 51–150 m, and in late summer 101–200 m and 951–1000 m with a slight concentration at 151–200 m (Table 119).