Bermuda Lantern Fish

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): 13 - 15; Analspines: 0; Analsoft rays: 21 - 23

Oceanic and mesopelagic (Ref. 4066), found between 600-800 m during the day, nyctoepipelagic at surface and down to 300 m (Ref. 4479). Reach sexual maturity at 5.8 cm (Ref. 47377).

Oceanic and mesopelagic (Ref. 4066), found between 600-800 m during the day, nyctoepipelagic at surface and down to 300 m (Ref. 4479). Reach sexual maturity at 5.8 cm (Ref. 47377).

Hygophum hygomii

This moderately large myctophid grows to a maximum size of 64 mm in the study area (68 mm is the known maximum; Hulley, 1981), but few specimens caught exceeded 60 mm. A temperate-semisubtropical lanternfish, it is most abundant in the North Atlantic temperate region (Backus et al., 1977). It is one of the “abundant” lanternfishes in the study area, ranking sixth in winter, 16th in late spring, and 20th in late summer (Table 131). The Ocean Acre collections contain 5350 specimens, more than 10 percent of the total number of lanternfish taken, but 3726 of these were taken with the Engel trawl during one cruise. Only 754 specimens were taken during the paired seasonal cruises; 521 of these in discrete-depth samples, of which 475 were caught in noncrepuscular tows.

DEVELOPMENTAL STAGES.—Postlarvae were 6–14 mm, juveniles 13–38 mm, subadults 27–63 mm, and adults 47–56 mm. Fewer than 10 adults were taken. Most juveniles less than 25 mm could not be sexed; most larger ones had small but recognizable ovaries or testes. About 89 percent of the winter juveniles and 59 percent of those taken in late spring could not be sexed. Females may grow faster than males; they attain a larger size and can be recognized at a smaller size than males (25 vs 27 mm). Of 78 specimens 56–64 mm long (almost all caught with the Engel trawl) only one 56 mm fish was a male. The dimorphism in size was most prominent in late summer: subadult males were 37–51 mm and averaged 43.0 mm, and subadult females 45–63 mm with a mean of 51.5 mm. Goodyear et al. (1972) also noted a sexual dimorphism in growth rate and size for H. hygomii in the Mediterrannean Sea, with females growing faster and becoming larger than males. Their material consisted mostly of adults. Presumably adults in the study area also would show this dimorphism. Males have a supracaudal luminous gland and females an infracaudal luminous gland.

REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Hygophum hygomii has a one-year life cycle, with only a few individuals living much longer than one year. Spawning apparently occurs in fall and winter, with a peak in intensity in late fall-early winter. Abundance was greatest in winter, when juvenile recruits 13–16 mm predominated; juveniles made up nearly 86 percent of the catch, with postlarvae accounting for most of the remainder. Abundance fell greatly between winter and late spring. By late summer abundance had reached a minimum, about of that in winter (Table 70).

Four females with eggs larger than 0.05 mm in diameter were taken from October to January. A 56 mm female taken in November contained the largest eggs (0.35 mm) and had greatly enlarged ovaries. Poor catches in November and December because of inclement weather, and in October-November because of the smaller 2-m IKMT used, may partially account for the paucity of adult females in the collections. Larger fish also may avoid the 3-m IKMT, judging from the difference between the catch made with the Engel trawl (3726 specimens) and the IKMT (7 specimens) in August-September. Postlarvae and juveniles at or near transformation size are most abundant in winter.

About 93 percent of all postlarvae were caught from January to March. The seasonal distributions of postlarvae, 13–16 mm juveniles, and the few females with relatively large eggs suggest that spawning takes place in fall and winter with a peak intensity in fall. The very low abundance of fish greater than 30 mm in winter suggests that most individuals die shortly after the spawning season at about one-year of age.

In late summer 97 percent of the poor discrete-depth catch consisted of subadults. As indicated above, the great number of specimens taken with the Engel trawl at the same time indicates that this estimate of abundance may be too low, because larger individuals avoid the IKMT.

In winter juvenile recruits 13–20 mm were predominant. Most of these were caught in February-March, suggesting that in January most of the population was represented by postlarvae. The few adults taken were males.

By late spring most recruits of the winter population had grown considerably and were large juveniles (greater than 20 mm) and subadults. Smaller juveniles were not very abundant, indicating that little spawning occurred in midto late winter. The tremendous decrease in abundance from winter to late spring (Table 70) is difficult to explain. Total abundance in late spring was only about 16 percent of that for juveniles in winter. It is possible that abundance was underestimated at this season because some individuals had grown large enough to avoid the net.

SEX RATIOS.—The sexes probably are equally abundant at all seasons, but sample sizes are too small to be reliable. Male-to-female sex ratios were 0.4:1 in winter, 1.6:1 in late spring, and 1.0:1 in late summer, with only the winter ratio statistically different from equality (Table 71). The difference in winter was due almost exclusively to juveniles, for which the female-to-male ratio was 3.0:1. However, only about 11 percent of the juveniles examined from winter collections could be sexed. Also, as indicated above, females may develop faster and, therefore, be recognized at a smaller size than males. All 25–26 mm juveniles that were sexed were females. When these individuals were excluded, sex ratios for large juveniles and total numbers were not significantly different from equality.

The difference in numbers of each sex also is statistically different from equality for juveniles in late spring. However, at that season juvenile males were more numerous than juvenile females, with a female-to-male ratio of 0.2:1. Again, this difference probably can be explained by different growth rates of the sexes. By late spring most winter females have become subadults while most males remain as juveniles. These differences in numbers of each sex for both stages cancel each other, although males are more numerous than females. Both sexes had developed into subadults by late summer and were present in about equal number (Table 71).

VERTICAL DISTRIBUTION.—Day depth range in winter was the upper 50 m and 501–1050 m with maximum abundance at 551–600 m, in late spring 51–100 m and 551–1000 m with a maximum at 651–700 m, and in late summer 701–800 m (Table 72). Nighttime depth range in winter was from the surface to 1050 m with maximum abundance at 51–150 m, in late spring the upper 100 m with a slight concentration at 50 m, and in late summer 51–100 m and 151–200 m with all but one specimen caught at the first depth.

Stage stratification was evident only during the day in winter and late spring. Size stratification was evident both day and night in winter and by day in late spring (Table 72). During the day in winter only postlarvae were caught at the shallow extreme of depth. Adults were taken only at 601–700 m, and juveniles and postlarvae were caught over much of the 501–850 m stratum. By day in late spring only postlarvae were caught at either extreme of depth and only juveniles at 551–650 m (Table 72). In terms of size, all specimens taken in the upper 100 m during the day in winter and late spring were 7–11 mm. During the day in winter fish less than 15 mm were most abundant at 701–750 m and 801–850 m, and those larger than 14 mm were taken mostly at 501–650 m. This stratification was evident from the mean of the catches at those depths, 14.1 and 13.7 mm vs 17.8 mm, respectively (Table 72). Badcock and Merrett (1976) caught transforming H. hygomii at 500–600 m in the eastern North Atlantic, and the above data indicate that transformation occurs below 700 m in the study area. In late spring, specimens 18–32 mm were caught only at 551–700 m, and those 33–35 mm only at 651–800 m.

At night in winter fish smaller than 10 mm and those larger than 20 mm were taken only in the upper 100 m, and specimens 13–16 mm were taken throughout the depth range (Table 72).

Postlarvae were stratified according to size in winter: smaller ones (6–9 mm) were caught only in the upper 100 m both day and night, and most of those larger than 9 mm were caught below 500 m. As is the case for other species, initial development occurs in the superficial layer and, at a size of about 9–10 mm, postlarvae descend to depths in excess of about 500 m where they continue to develop and transform into juveniles.

Diel vertical migrations occurred at all seasons, but only in late spring and late summer was the entire night catch taken above daytime depths (Table 72). In winter the population included nonmigrants, partial migrants, and complete migrants. Migrants were 13–34 mm (and probably larger); partial migrants and nonmigrants were 13–19 mm, but mostly 13–16 mm. Postlarvae probably do not migrate over any extensive depth range, as migratory behavior apparently is adopted on a regular basis at a size of about 17 mm. Almost all individuals larger than 16 mm were taken in the upper 200 m at night. The smallest juveniles (13 mm) were taken only at 101–150 m and 751–800 m and contained the largest proportion of nonmigrants (71 percent). Juveniles 14–16 mm were taken at all depths; less than 50 percent of these were partial migrants and nonmigrants. Although the late spring population contained juveniles within the size range of winter partial migrants and nonmigrants, all night captures were made in the upper 100 m.

Little could be determined concerning the chronology of diel vertical migrations in late spring and late summer due to sparse catches in the upper 100 m until well after sunset. In winter the onset of evening migrations was difficult to determine, because the population included nonmigrants. The upper 200 m was occupied by 0.5 hour after sunset, the upper 150 m by 1.4 hours after sunset, and the upper 100 m by 2.7 hours after sunset. As these are all the latest times of arrival, actual times of arrival may be earlier, particularly the last, which is based upon the first sample made within the upper 100 m after sunset.

PATCHINESS.—Patchiness during daytime was evident only in winter at 701–750 m and 801–850 m. No samples were taken at 651–700 m, 751–800 m, and 851–1000 m, and patchiness may have been more extensive than indicated. More than 95 percent of the catch from the depths at which clumping was indicated was made up of 13–14 mm juveniles. By day in winter larger juveniles (15–25 mm) were most abundant at 551–600 m, where no patchiness was indicated.

Patchiness was more prevalent at night. Significant clumping was noted in winter at 18–100 m and in late summer at 51–100 m. In winter juveniles were most abundant at 18–100 m (postlarvae were not included in the analysis), and in late summer the catch at 51–100 m was almost exclusively subadults.

Significant CD values were obtained for nocturnal surface samples in winter and late spring. However, these probably reflect a low population density rather than patchiness. More than 45 nocturnal surface samples were taken in both seasons, only three in winter and two in late spring were positive; one of the positive samples contained two specimens, the rest only a single specimen.

NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios, including interpolated values, were 0.6:1 in winter, 0.3:1 in late spring, and 2.9:1 in late summer (Table 73). The ratios for the developmental stages followed the overall seasonal trends. Juveniles were responsible for most of the diel differences in the catches in winter and late spring, and subadults in late summer.

In winter most of the difference between day and night catches was due to 13–14 mm juveniles for which the night-to-day catch ratio was 0.3:1. The 13 mm juveniles were about 10 times more abundant in day samples than in night samples. The nighttime vertical range of these juveniles was much greater than the daytime range, and patchiness was more prevalent at night, both of which may have contributed to the difference between the day and night catches. Net avoidance probably is not an important factor, because the catch was mostly smaller than 20 mm both day and night.

In late spring the poor night catches may be a result of inadequate discrete-depth sampling in the upper 150 m, and particularly the upper 50 m (Figure 2). The night depth range was compressed compared to the daytime range, yet the day catch was greater than the night catch (Table 72). Increased net avoidance may account partly for the difference in catches, for all specimens greater than 40 mm were caught in day samples.

In late summer the population was mostly 45 mm and larger. Apparently, H. hygomii of this size can avoid the 3-m IKMT both day and night. That large fish were present in some abundance at that season is indicated by the catch of H. hygomii made with the Engel trawl. As both the day and night catches with the IKMT were small (less than 4.0 specimens/hour), it is assumed that H. hygomii was not adequately sampled either by day or by night.

Canada to 20°N and from Brazil to subtropical convergence

oceanic and mesopelagic, found between 600-800 m during the day, nyctoepipelagic at surface and down to 300 m

nektonic

Known from seamounts and knolls