Dofleini's 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.

Dorsal spines (total): 0; Dorsal soft rays (total): 15 - 14; Analspines: 0; Analsoft rays: 13 - 15

High-oceanic, found between 300-750 m during the day and between 20-400 m at night. Size stratification observed with depth. Feeds nocturnally or during vertical migration, mainly on copepods and ostracods .

High-oceanic, found between 300-750 m during the day and between 20-400 m at night (Ref. 4066). Size stratification observed with depth (Ref. 4479). Feeds nocturnally or during vertical migration, mainly on copepods and ostracods (Ref. 4775).

Lobianchia dofleini

This medium-size lanternfish is known to grow to 45–50 mm (Nafpaktitis et al., 1977); the largest specimen in the Ocean Acre collections is 38 mm. Lobianchia dofleini, a bipolar temperate-semisubtropical species, is a ranking myctophid in the North Atlantic subtropical region (Backus et al., 1977). The Ocean Acre collections are in agreement with this. The species is one of the abundant myctophids found near Bermuda, and was among the 15 most abundant lanternfishes at each of the three seasons, ranking third in late spring when it was most abundant (Table 131). It is represented in the Ocean Acre collections by 3749 specimens; 964 were caught during the paired seasonal cruises, 601 of these in discrete-depth samples, of which 413 were caught in noncrepuscular tows (Table 23). The biology of L. dofleini in the study area has been discussed elsewhere by Karnella and Gibbs (1977). The account given here is similar to that presented by those authors and is included for the sake of making the species accounts complete.

DEVELOPMENTAL STAGES.—Postlarvae were 4–10 mm, juveniles 10–24 mm, subadults 19–36 mm, and adults 24–34 mm. Generally only the largest juveniles, 16 mm and larger, could be sexed. Adult females contained eggs as large as 0.6 mm, but mostly 0.2–0.3 mm in diameter. Sexual dimorphism was apparent externally at 18–21 mm, with males developing supracaudal luminous tissue and females infracaudal luminous tissue. Females may grow larger than males. The largest female was 36 mm, the largest male 33 mm (two 38-mm specimens were not sexed); nearly 64 percent of the sexed fishes larger than 29 mm were females. Taaning (1918) and Nafpaktitis (1968) reported that males have noticeably larger eyes than females.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.— The species has a one-year life cycle. It breeds from January (possibly December) to June, with a peak of spawning intensity in winter. It was most abundant in late spring, intermediate in late summer, and least abundant in winter. The catch in each season was dominated strongly by a different developmental stage; juveniles were predominant in late spring, subadults in late summer and adults in winter. In each season the dominant stage accounted for about 80 percent of the total catch (Table 112).

Although adult-size females were caught throughout the year, only in winter did many have eggs larger than 0.1 mm in diameter. Most (15) of the relatively few postlarvae (19) caught were taken from February to May. Small juveniles 10–15 mm were caught from February to September and were most abundant in late spring. These seasonal distributions indicate a winter peak in spawning. The capture of postlarvae and small juveniles (10–15 mm) over much of the year suggest a long spawning season for L. dofleini in the study area.

In winter, spawning was at or near a peak, abundance was lowest, and adults comprised nearly 80 percent of the abundance (Table 112). None of the other stages accounted for more than 10 percent of the abundance. The capture of postlarvae and small juveniles in low abundance shows that a minimum of spawning occurred over the fall. Most of the specimens caught in winter were larger than 25 mm.

In late spring recruits from the spawning peak were mostly 10–25 mm juveniles. These individuals made up about 80 percent of the total abundance. The abundances of adults and specimens larger than 25 mm were much lower than in winter, reflecting postspawning mortality. The increase in the abundance of subadults from winter to late spring was partially due to growth of the earliest spawned individuals; some were adult size and probably were spent during the recent spawn and would die soon.

By late summer there was little additional recruitment, as indicated by the low abundance of all individuals smaller than 22 mm. Continued growth and development in the recruit class resulted in an increase in the abundance of subadults and a decrease in the abundance of juveniles (Table 112). Adult abundance remained at its low, late spring level. All adults were males (Table 113), indicating that spawning was completed by early to midsummer.

O'Day and Nafpaktitis (1967) and Nafpaktitis (1968) concluded that L. dofleini spawned only east of 34° and south of 48° in the North Atlantic, and that it was nonbreeding in the western and northern Atlantic, maintaining its population in the expatriate region by periodic recruitment from the spawning area to the east. These authors found neither gravid females nor juveniles less than 16 mm in the western North Atlantic north of Cape Hatteras. Histological preparations made by O'Day and Nafpaktitis (1967) showed that female L. dofleini in the western North Atlantic had only oogonia and oocytes and no large yolk-filled eggs in their ovaries. The oocytes appeared to be normal, but had not undergone vitellogenesis. It was noted that males in the expatriate area had testes that contained mature sperm.

O'Day and Nafpaktitis (1967) noted the presence of 11–12 mm juveniles off Cape Hatteras but offered no explanation for this. Presumably those small specimens were transported from the spawning area via prevailing currents, a crossing that O'Day and Nafpaktitis hypothesized would take about a year, i.e., the total life span of most specimens found near Bermuda. Because this species is known to transform to the juvenile stage at 11–13 mm (Taaning, 1918), the proposed system of recruitment would involve a larval stage nearly a year in duration. Furthermore, as O'Day and Nafpaktitis (1967) observed, the population density of L. dofleini in the expatriate area is almost as large as that in the spawning area. This implies that truly astronomical numbers of this species must be transported from the spawning area to account for the population density in the western North Atlantic. One would expect the population density in the spawning area to be much greater than, and not about the same as, that in the expatriate area.

Finally, O'Day and Nafpaktitis (1967) did not examine females collected at all times of the year. Most of their material was collected from June through October; only one female was taken between November and March. The present study shows that Bermuda has a breeding, not expatriated, population that spawns primarily in winter. If L. dofleini found in slope water off the continental United States is a reproductive population, spawning mainly in winter, it is quite possible that O'Day and Nafpaktitis found no gravid females because winter collections were not available.

The Ocean Acre collections analyzed here, the normal but undeveloped oocytes and the mature sperm present in males observed by O'Day and Nafpaktitis, the large population density in the slope water, and the appearance of 12 mm juveniles off Cape Hatteras all speak against the hypothesis of sterile expatriation and indicate that L. dofleini maintains a reproductive population in the western North Atlantic.

SEX RATIOS.—Males and females probably were equally abundant at all seasons. They were taken in about equal numbers both in late spring and late summer, and more females than males were taken in winter (1.3:1), but the latter difference was not significant (Table 113). Juvenile males were more numerous than juvenile females in late spring and late summer. Subadult females were more numerous than subadult males in all three seasons. Adult males were more numerous than adult females in late spring and late summer, and less numerous than adult females in winter, when adults were most abundant. The only significant difference from equality was for juveniles in late summer (Table 113), and this probably reflects sexual dimorphism in rate of development rather than a fundamental difference in the numbers of each sex.

VERTICAL DISTRIBUTION.—Diurnal vertical range in winter was 1–50 m and 351–750 m with maximum abundance at 451–500 m, in late spring 351–700 m with a maximum at 601–650 m, and in late summer 451–650 m with a maximum at 501–600 m. Depth range at night in winter was 51–200 m (a 10 mm specimen was taken at 18–19 m) with no apparent concentration within that range, in late spring 50–200 m with a maximum abundance at 50 m, and in late summer 90–175 m (a 16 mm juvenile was caught at 33 m) with a maximum at about 100 m (Table 114).

Stage and size stratification were evident at each of the three seasons and, except for size stratification by day in late spring, were apparent both day and night. By night at all seasons juveniles were most abundant at shallower depths and had a shallower upper depth limit than adults. In terms of size, the largest fish were taken only at the lower depth limit at all seasons, and in winter and late summer the smallest individuals were taken only at the shallower depth limit. Nocturnal stratification was indicated by the increase in mean size with depth (Table 114).

By day in late spring juveniles and subadults were most abundant at 601–650 m and had similar depth ranges, but juveniles were more abundant above than below 600 m, while the opposite was true for subadults. Only one adult was caught during the day at this season. Small (11–13 mm) and large (25–36 mm) fish were caught only at or near the lower depth limit, while those of intermediate size were taken at all depths within the vertical range (Table 114).

In late summer during the daytime juveniles were most abundant at a shallower depth than subadults and adults, and they and subadults had a shallower upper depth limit than adults. Small juveniles (11–13 mm) were caught only near the lower depth limit, and there was a slight increase in the mean size with depth (Table 114).

By day in winter, stratification apparently was reversed. Adults were most abundant at a shallower depth and had a shallower upper depth limit than the few juveniles and subadults, and juveniles were taken only below the deepest depth at which advanced stages were taken. Fish 10–11 mm were caught only below 500 m, those 26–30 mm were all from shallower depths; a single postlarva was caught in the upper 50 m (Table 114).

Diel migrations occurred at all three seasons and apparently by all stages and sizes. Only one fish, a probable contaminant from a previous tow, was caught at daytime depths during the night. Recently metamorphosed juveniles (10–11 mm) were taken only at or near the deepest day depths and at or near the shallowest night depths both in winter and late spring, suggesting that they may undertake more extensive diel migrations than older fish (Table 114).

Evening migrations were about 2.0 hours in duration in late spring and as long as 3.0 hours in winter and late summer. (Almost certainly they were of shorter duration, because the population at the latter two seasons was mostly made up of larger fish than in late spring). Day depths still were occupied about an hour before sunset in late spring (520 m), about 2.5 hours before sunset in late summer (∼650 m), and about 2.0 hours before sunset in winter (535 m). In late summer a single individual was taken at between 470 and 500 m at about sunset. Nocturnal depths were reached within an hour after sunset at all three seasons. Based on these times, estimated migration rates between day and night depths of maximum abundance are about 300 m/hour in late spring, about 140 m/hour in late summer, and about 120 m/hour in winter.

The duration and rate of morning migrations were similar to evening migrations at each of the three seasons. Descent to diurnal depths apparently starts about the time of sunrise, as specimens were caught in the upper 200 m at or near that time in all three seasons. Daytime depths were reached about 2.0 hours after sunrise in late spring (∼475 m) and about 3.0 hours (perhaps less) after sunrise in winter (∼400 m and ∼750 m) and in late summer (∼575 m).

Captures were made at several intermediate depths at or near sunset in late spring and late summer, and at or near sunrise in late spring, suggesting that different migration rates or times or both may exist in various elements of the population.

PATCHINESS.—Patchiness at night was indicated at 50–100 m in late spring and at 51–100 m in late summer. In late spring each of the three most advanced developmental stages occurred in maximum abundance in this interval, but probably only juveniles had a patchy distribution. They accounted for more than 95 percent of the catch at 50–56 m and, hence, were responsible for the observed variation in the catch from that depth. Between 90 and 100 m, where more than 60 percent of the catch consisted of juveniles, two samples from about 90 m, containing almost exclusively juveniles, suggested clumping, while three samples at 100 m, containing mostly subadults, did not. In late summer clumping was indicated for juveniles and subadults at 51–100 m. Juveniles were most abundant at this depth, but subadults accounted for more than 70 percent of the catch from that depth interval. Subadults were most abundant at 101–150 m, but showed no clumping.

CD values were significantly greater than 1.0 in late summer at night at 151–200 m and during the day at 101–150 m, 451–500 m and 501–600 m, and during the day in late spring at 551–700 m. The significant CD value obtained at 151–200 m at night in late summer resulted from a series of three negative samples taken during one cruise being tested with a series of three samples, two of which were positive, from the other cruise. CD values calculated for each series separately were not significantly greater than 1.0. Additionally the positive samples were taken near the morning crepuscular period and may have caught early migrants.

The CD value for 501–600 m during the day in late summer barely was significant, and the catches suggest a random distribution. At 451–500 m only one sample was positive, suggesting a low population density at the upper day depth limit. At 101–150 m, a depth much too shallow to be within the diurnal vertical range, only one sample taken near the evening crepuscular period was positive, suggesting that the catch included migrants. By day in late spring at 551–700 m the distribution may be patchy, but more likely is random, similar to that of 501–600 m by day in late summer, only at a lower population density. Patchiness was not indicated in winter for any stage at any depth day or night.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios for discrete-depth captures, including interpolated values, were 0.5:1 in winter, 4.2:1 in late spring and 1.2:1 in late summer (Table 115).

Seasonal differences in clumping, abundance, vertical distribution, discrete-depth coverage, and stage and size composition render it most unlikely that any one factor was the principal cause of the observed differences in diel catch rates. Adults were most abundant in winter and accounted for most of the difference between night and day catches at that season. Juveniles had the greatest proportional difference between day and night catches but they comprised little more than 10 percent of the day abundance and less than 5 percent of the night abundance. Increased net avoidance at night by adults may have been responsible for the higher daytime catches in winter.

Apparently, L. dofleini feeds at night or during migrations (Merrett and Roe, 1974), and increased activity associated with feeding may result in enhanced net avoidance. The two largest catches of L. dofleini in winter were made in discrete-depth samples taken at 130 m and 140 m at about dusk and dawn, respectively. Night discrete-depth samples were taken at 100 m and 150 m but not between, suggesting the depth of maximum abundance of L. dofleini was not sampled, and as a result the abundance at night was artificially low.

Juveniles were responsible for most of the difference between late spring day and night catches, and subadults for most of that in late summer. Patchiness was greater and the vertical range more compressed at night than during the day at these seasons. These differences may have resulted in increased night catches.

Lobianchia dofleini, Dofleini's lantern fish, is a species of lanternfish. The fish is found in the {Atlantic Ocean]].

Feeds nocturnally or during vertical migration, mainly on copepods and ostracods

Atlantic Ocean: between 50°N and 40°S including the Mediterranean but with a distributional gap between 8°S and 13°S in the eastern Atlantic, absent in the South Sargasso Sea and minimum region off Brazil; southern circumglobal

high-oceanic, found between 300-750 m during the day and between 20-400 m at night

nektonic

Known from seamounts and knolls

Epipelagic

Mesopelagic