Lanternfish

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

Mesopelagic (Ref. 5951).

High-oceanic, found between 325-750 m during daytime (Ref. 4479). At night, a two layer system occurs, with adults found at 300-600 m and juveniles at 40-200 m (Ref. 4479).

Diaphus rafinesquii

This is a large myctophid, growing to 89 mm in the study area (Gibbs et al., 1971), which is about the maximum size attained (Nafpaktitis et al., 1977). The species reaches sexual maturity at about 65 mm (Nafpaktitis, 1968; 50 mm according to Taaning, 1918). A common temperate-semisubtropical species (Backus et al., 1977) it is most abundant in the North Atlantic temperate region (Nafpaktitis et al., 1977). It is common near Bermuda, being represented in the Ocean Acre collections by 342 specimens; 193 were caught during the paired seasonal cruises, 128 of these in discrete-depth samples, of which 93 were caught in noncrepuscular tows.

DEVELOPMENTAL STAGES.—The one postlarva was 11 mm, juveniles 9–26 mm, subadults 61–87 mm, and the only adult (a male) 66 mm. All juveniles had small, barely discernible gonads that could not be sexed under the dissecting microscope. Females showed little development of ovaries or eggs, with most eggs less than 0.1 mm in diameter, the maximum size observed. Subjectively, males seemed to be more developed sexually than females. Males had a larger Vn than females of a comparable size. There also may be a sexual dimorphism in size. Males were 61–82 mm and females 65–87 mm. A greater proportion of females than males were larger than 70 mm (37 vs 17 percent). Data given by Goodyear et al. (1972) for fish taken in the Mediterranean Sea also show a difference in size for the sexes; adult males were 53–69 mm and adult females 54–78 mm.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—The life history of D. rafinesquii in the study area is quite complex and, as is the case with D. metopoclampus, may involve migrations into and out of the study area. Spawning probably does not take place in the study area. Therefore, the population must be maintained by recruitment from outside, possibly from the north or northeast. The parent population spawns in fall-winter. The life span probably is at least two years.

Abundance was greatest in late spring, when the catch consisted only of subadults in excess of 60 mm. It was intermediate in winter and least in late summer. In winter juveniles accounted for nearly 70 percent of the catch (Table 52).

All specimens were either 9–31 mm or 61–87 mm. Small fish were taken from January to April. All those 9–12 mm were caught in January. Large fish were taken at all seasons and constituted the entire catch from June to December.

The lack of specimens 32–60 mm in the Ocean Acre collections, although puzzling, probably reflects the situation in the study area rather than a sampling bias. This suggests that by April most young specimens have either died or migrated out of the study area. Therefore, large fish must migrate into the area to maintain their numbers. To account for their presence at all seasons, they must either be able to survive in the area or must migrate into the area on a regular or periodic basis. This situation apparently is unique to the study area. Most of the missing sizes have been taken east of the area (Hulley, personal communication), in the Mediterranean Sea (Goodyear et al., 1972), in slope water near Hudson Canyon (Krueger et al., 1975; personal observation), and near the Canary Islands (Badcock, 1970). Although all females captured in the study area were larger than the reported size at sexual maturity for other populations of D. rafinesquii (Taaning, 1918; Nafpaktitis, 1968; Goodyear et al., 1972), none were ripe or nearly so. Nafpaktitis (1968) suggested that the species is an expatriate in the western North Atlantic and that spawning does not occur west of 40°W. Although the absence of ripe females in the collections would support this hypothesis, the recruitment of juveniles 9–12 mm (the size at metamorphosis; Taaning, 1918) in January does not, and suggests that there may be a breeding population not too distant from Bermuda. In any case, the parent population must spawn in fall or winter, the spawning season in the Mediterranean Sea (Taaning, 1918; Goodyear et al., 1972), to account for the capture of such small recruits.

In winter small fish predominate. These juveniles are mostly 9–12 mm in January and 18–21 mm in February. By late spring all small fish have died or left the area, and the catch consists exclusively of subadults. Abundance in late spring is nearly twice that in winter (Table 52), suggesting that there has been a migration of large fish into the study area. By late summer abundance is drastically reduced, with only a few 60–65 mm specimens being caught. This reduction in abundance may be due to failure of large fish to survive in the area or to their migrating out of the area.

It is unlikely that the largest juveniles caught in winter (26 mm) and the smallest subadults in late spring (63 mm) represent the same recruit class at different ages. The capture of large fish at all seasons suggests a life span of at least two years.

SEX RATIOS.—Fewer than 10 subadults and adults were taken in either late summer and winter, with the sexes about equally numerous in the collections (Table 53). In late spring females were slightly more numerous than males with a ratio of 1.2:1.

VERTICAL DISTRIBUTION.—Depth range by day in winter was 451–650 m with maximum abundance at 451–500 m, in late spring 451–700 m with no apparent concentration at any depth, and in late summer three fish were taken at 601–650 m. Nocturnal vertical range in winter was 40–200 m and 351–550 m with a slight concentration at 51–100 m, in late spring 351–600 m with a maximum abundance at 501–550 m, and in late summer one fish was taken at 451–500 m (Table 54).

Stage and size stratification were evident day and night in winter, and size stratification by night in late spring.

By day in winter juveniles 15–20 mm were taken at 451–500 m, those 10–11 mm at 601–650 m, and one subadult was taken at 501–550 m and another at 601–650 m. At night in winter all juveniles were taken in the upper 200 m, while subadults were all from 351–550 m. Juveniles were stratified by size, those 10–12 mm long were from 151–200 m and those 23–26 mm from 51–100 m; intermediate sizes were taken at 40–200 m. Subadults also showed a size stratification during the day with an increase in maximum and mean size with depth, but only five fish were taken (Table 54).

By night in late spring larger subadults (77–82 mm) were taken only at 551–600 m, and those 64–76 mm were taken throughout the range. Mean and maximum sizes increased with depth from 451–600 m (Table 54).

Only juveniles undergo extensive diel migrations, but at least some subadults show a slight change in depth over a 24 hour period.

In winter all juveniles were taken at 40–200 m at night, or about 300–450 m shallower than day depths. Few subadults were taken by day, but in each season the upper depth limit at night was shallower than by day. Although this could be due to enhanced diurnal net avoidance, a slight upward shift of at least some large fish seems a more likely cause for the shallower upper depth limit at night. Goodyear et al. (1972) noted a similar restricted diel migration in large D. rafinesquii in the Mediterranean Sea, with small fish having a more extensive diel migration. Badcock (1970) and Badcock and Merrett (1976) noted a similar pattern in the eastern Atlantic.

PATCHINESS.—A patchy distribution was indicated at night at 51–100 m in winter and at 451–500 m in late spring. Only juveniles were caught at 51–100 m in winter, and only subadults were taken at 451–500 m in late spring.

The significant CD value obtained for samples taken in the upper 50 m in winter may have been due to a vertical concentration rather than horizontal patchiness. Of 10 samples made at 18 m, 34 m, 40 m, and 50 m, only the single sample at 40 m was positive.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios (including interpolated values) for discrete-depth captures were 1.1:1 in winter, 6.5:1 in late spring, and 0.1:1 in late summer (Table 55).

In late spring, when the catch was exclusively subadults, the night catch was considerably greater than the day, suggesting that there was greater net avoidance during daytime. However, there was a diel difference in patchiness, which could have affected catch rates. Sample sizes were so small in late summer that catch rates have little reliability.

The white-spotted lantern fish (Diaphus rafinesquii), also called Rafinesque's lanternfish, is a species of fish in the family Myctophidae.

Western Atlantic: north of the Gulf Stream

Found at depths of 40- 1080 m.

nektonic