Comprehensive Description
provided by Smithsonian Contributions to Zoology
Ceratoscopelus warmingii
This is a moderately large species growing to 81 mm (Hulley, 1981); maximum size in the Ocean Acre collections was 75 mm. A ubiquitous tropical-subtropical species, C. warmingii is a dominant lanternfish found in the North Atlantic subtropical region (Backus et al., 1977). Near Bermuda, C. warmingii is one of the “abundant” myctophids, being among the eight most abundant at each of the three seasons sampled (Table 131). A total of 4683 specimens was caught; 1862 were taken during the paired seasonal cruises, with 1226 of these from discrete-depth samples, 818 of which were from noncrepuscular tows (Table 23).
DEVELOPMENTAL STAGES.—Postlarvae were 5–18 mm, juveniles 15–41 mm, subadults 35–36 mm, and adults 43–75 mm. Juveniles smaller than 25 mm could not be sexed; most of those 25–35 mm and all larger ones were sexed. Of those categorized as subadults, females larger than about 55 mm and males larger than about 45 mm may have been spent or recovering adults. Sexual dimorphism in size is apparent in the three older stages, with adult females (53–75 mm) averaging nearly 10 mm larger than adult males (43–55 mm). Adult females contained ova as large as 0.5 mm in diameter, but most eggs were 0.2–0.3 mm. Luminous tissue (other than photophores), for which no sexual dimorphism was apparent, was developed on fish 22–29 mm, sizes 6–13 mm smaller than reported by Nafpaktitis et al. (1977).
REPRODUCTIVE CYCLE AND SEASONAL ABUNDANCE.—Ceratoscopelus warmingii apparently has a one-year life cycle. Spawning takes place from spring to fall, perhaps extending into winter, with a peak in late spring. Most individuals live about a year and apparently some live longer, perhaps as long as two years. Abundance was lowest in late spring, although all stages except juveniles had their greatest abundance then (Table 40). In both late summer and winter total abundance, which was dominated by juveniles, was about 60 percent greater than that of late spring.
Adult-size females were caught at all seasons, but only from April to October did any of them have enlarged ovaries that either contained ova 0.2 mm or larger or looked spent. There is some indication that spawning may not occur continuously from spring to fall. None of the adult-size females (28 specimens) taken in July had large eggs (all were less than 0.1 mm), and most of them appeared to be in a postspawning condition.
Although they occurred over much of the year, postlarvae were most common from June to October; less than 5 percent of the total came from collections made at other times. They were most numerous in July, when nearly half the total number were caught. Small juveniles (smaller than 25 mm) were abundant in late summer and winter but virtually absent in late spring. Juveniles of all sizes made up nearly 90 percent of the catch in late summer, 80 percent in winter, and slightly more than 10 percent in late spring (Table 40).
The catch in late spring was dominated by subadults and postlarvae, which together accounted for 75 percent of the catch. Juveniles and adults were less and about equally abundant (Table 40). Adults were more than three times as abundant in late spring as in the other two seasons. This, together with the maximum abundance of subadults, suggests that spawning was at or approaching a peak. The presence of fair numbers of postlarvae shows that spawning commenced earlier in the spring. The paucity of juveniles, especially those smaller 33 mm, indicates that minimal spawning occurred over winter.
Larger fish in late spring showed strong sexual dimorphism in size. All those smaller than 43 mm were males, and all but two larger than 50 mm were females (males were 33–54 mm, and females 44–60 mm). Presumably, most of the larger fish of each sex were about a year old and had spawned recently or would spawn soon. Smaller fish probably were spawned the previous fall and had not yet grown to adult size. Males larger than about 50 mm and females larger than about 55 mm may have been more than one year old.
Recruits from the spring spawn dominated the catch in late summer. Juveniles accounted for more than 87 percent of the catch at night, with those 17–26 mm accounting for more than 68 percent and those 27–40 mm an additional 19 percent. Postlarvae made up about half of the remaining catch (Table 40). The largest juveniles probably represent the vanguard of the spring spawn, and the smaller group presumably was spawned near the peak in June. The reduced abundance of large fish (subadults and adults combined were about one-sixth as abundant as they were in late spring) suggests that most spawning already had occurred. Most subadults and adults caught in late summer were later spawners approaching one year in age. Some larger males (larger than 55 mm) probably were more than one year old and presumably had spawned in the spring.
Winter collections were dominated by recruits from the fall spawn, with fish smaller than 26 mm comprising more than 50 percent of the night catch (these fish were poorly sampled during the day). The catch of fish smaller than 26 mm at night in winter was about two-thirds that of the night catch of fish of the same size in late summer, which is assumed to reflect a decrease in spawning intensity between spring and fall. A peak at 17 mm, representing recently transformed fish, was entirely due to the catch in January and was not seen in late February. If the latest spawning occurred in October-November, development to the juvenile stage took between two and three months. Larger juveniles (25–35 mm) caught in winter probably were spawned the previous late spring and were 7–8 months old. Sexual dimorphism in size was evident in these larger juveniles, and females were, on the average, larger than males (33.0 vs 30.3 mm). Most winter subadults would be the earliest spawned and be about 9–10 months old. Fish larger than 55 mm were all females and may have been in their second year; perhaps some of the larger males also were. Most of these larger fish presumably had spawned during the previous season.
SEX RATIOS.—Significant differences from equality were noted for subadults at all seasons, males being more numerous in late spring and late summer and females in winter, with total male-to-female sex ratios of 2.6:1, 1.5:1, and 0.8:1, respectively (Table 41).
The difference observed in late spring may be due, at least in part, to a spatial segregation between the sexes at certain depths and times. Excluding postlarvae, 48 spiecimens, mostly subadults, were caught at about 50 m between 0200 hours and sunrise; the 45 that could be sexed were males. In winter at about 100 m at the same time discrete-depth samples caught 228 fish, mostly unsexable juveniles; of the 56 that could be sexed, 52 were females (60 percent were juveniles and 40 percent subadults). Samples from about 100 m between 0200 and 0300 hours in late spring and between 2100 and 2400 hours in winter contained about equal numbers of each sex, indicating that spatial segregation between males and females did not occur at all depths and times. Unfortunately, this matter could not be pursued in greater detail because most large samples in winter and late summer contained relatively few sexable fish, and in late spring, when nearly all fish could be sexed, most positive samples contained fewer than 10 specimens.
VERTICAL DISTRIBUTION.—Day depths of occurrence in winter were 601–1550 m with maximum abundance at 1001–1200 m, in late spring 50–100 m, 351–400 m, and 651–1100 m with a maximum at 1051–1100 m, and in late summer 751–1150 m with a maximum at 801–850 m. Night depths in winter were 20–200 m, 801–900 m, and scattered between 301 and 600 m, with maximum abundance at 51–100 m and a secondary concentration at 801–900 m. In late spring, night depths were 50–100 m and scattered at 451–800 and 951–1000 m, with a maximum at 50–100 m. In late summer, night depths were 33–200 m, 851–1000 m, and scattered between 301 and 700 m, with a maximum at 51–100 m (Table 42).
Fish caught at 601–650 m during the day in winter actually may have been migrants. Eleven other daytime samples taken between 580 and 850 m failed to capture C. warmingii. The only positive sample, which caught five specimens, was made near the evening crepuscular period. The two following crepuscular samples during the same trawl had even larger catches (30 and 39 specimens per hour).
Stage stratification was evident day and night in late summer and during the day in late spring. Size stratification was evident day and night at all three seasons.
During the day in late summer the vertical range of juveniles encompassed that of other stages, but juveniles were concentrated at the upper limit of their range, which was shallower than the adult range and at the shallow end of the subadult range. Both subadults and adults were rather uniformly distributed vertically. In late spring only postlarvae were found shallower than 950 m during the day (Table 42).
Size stratification by day was well developed in late spring and late summer, and was weakly developed in winter. In late spring all fish caught above 900 m were postlarvae 7–16 mm, those from 950–1000 m were 14–50 mm, and those from 1051–1100 m were all greater than 36 mm. In late summer more than 95 percent of the catch from 751–850 m was 15–22 mm, and all fish from greater depths were larger than 22 mm. The mean size of the catch from 751–850 m was less than 20 mm; from greater depths it was more than 30 mm. In winter the smallest fish caught during the day were all from 601–650 m but, as suggested, these may have been migrants. The catch at 1001–1050 m averaged at least 3 mm smaller than that from deeper 50 m intervals (Table 42).
At night in late summer only postlarvae and juveniles were caught above 50 m. At that season the catch from the upper 50 m was 17–26 mm (only one specimen larger than 20 mm); at 51–200 m it was 8–63 mm (only two larger than 50 mm); and at day depths (nonmigrants) it was 13–18 mm. Only five specimens were caught at intermediate depths. The mean size of the catch at 30–50 m and 851–1000 m was distinctly smaller than that at 51–200 m, where most of the catch was taken (Table 42).
In late spring more than 95 percent of the night catch from the upper 50 m, and only about 50 percent of that from 51–100 m, was 45 mm or smaller. All fish larger than 54 mm were caught at 51–100 m. The mean size of the catch at 51–100 m was 13.6 mm larger than from the upper 50 m (Table 42).
In winter all sizes, including most of the larger specimens, were caught in the upper 100 m at night, but most small fish (less than 20 mm) were taken at depths greater than 100 m. All specimens taken at day depths (nonmigrants) at night were 15–18 mm (Table 42). During late February and early March the spacing of samples detected a smaller scale stratification of fish caught at 51–100 m. Mean sizes were 30.9 mm at 68 m, 38.1 mm at 95 m, and 53.5 mm at 100 m.
Postlarvae were stratified by size in late spring and late summer and probably do not migrate vertically. In late spring most smaller postlarvae (less than 14 mm) were caught in the upper 100 m; all those between 14–18 mm were caught below 750 m both day and night. At night in late summer postlarvae 6–12 mm were caught in the upper 150 m, those 14–16 mm were caught at 851–1000 m, and 13 mm specimens were caught in both strata. Only one postlarva was caught during the day in late summer (Table 42). Postlarvae clearly spend the early part of their lives in the upper 100–200 m and, upon reaching 11–13 mm, descend to the deeper stratum where they continue to develop and metamorphose into juveniles before migrating regularly.
Diel vertical migrations occurred at all three seasons, but at each season part of the night catch came from daytime depths. Very few fish were caught at intermediate depths (201–700 m) at night in each season; those caught in late summer were 21–31 mm, those in winter 18 mm (one specimen) and 31–61 mm, and in late spring 46 mm (one specimen). Nonmigrants were all smaller than 20 mm, but fish of those sizes also were migrators.
All but one of the few 15–16 mm specimens caught at night were from day depths. Fish 17–19 mm were caught during the night at diurnal depths and also in the upper 200 m both in winter and late summer, indicating the onset of migratory behavior at this size range. Most 19 mm fish and all larger fish were caught only above day depths at night. Nonmigrants, including postlarvae, accounted for about 25 percent of the night catch in winter, about 6 percent of that in late spring, and 9 percent of that in late summer. Clarke (1973) noted that, near Hawaii, 15–19 mm fish were taken both in the upper 100 m and at 600–700 m, and that larger fish migrated regularly.
Little could be determined about the chronology of vertical migrations of C. warmingii in late spring, and only crude estimates of migration times and rates could be made for winter and late summer. In late spring a single fish was caught near 200 m within an hour after sunset. There were no positive day samples from shallow depths after 1000 hours; the earliest positive night sample in the upper 100 m was 2.5 to 3.5 hours after sunset, and the earliest sample at 50 m (it was positive) started at 0200 hours.
In winter, day depths were still occupied at about 2.5 hours before sunset (and possibly until 1.5 hours or less). Specimens were taken at 650 m and 225 m no more than 0.5 hour after sunset, and at 130 m no more than 1.5 hours after sunset. Fish were captured in the upper 100 m at least 2 to 3 hours after sunset; no samples were taken in the upper 100 m between sunset and those times, so it is possible that fish arrived in the upper 100 m earlier. Assuming that upward migrations were on the order of 3.5 hours in duration, migration between day (1050 m) and night (100 m) depths of maximum abundance averaged about 270 m/ hr. Several specimens were caught at about 140 m within an hour of sunrise, but there were no positive day samples until 5 hours after sunrise.
In late summer the latest positive day sample ended more than 2 hours before sunset, but it was taken near the upper depth limit and caught only one specimen. Presumed migrants were taken at 301–350 m and 451–500 m no more than 1.3 hours before sunset. Fish reached the upper 50 m by 1.5 hours after sunset. This results in a migration time of about 2.5 hours and a migration rate of 160 m/hr between 500 and 100 m. Migration time between diurnal and nocturnal depths of maximum abundance (850 m to 100 m) would approximate 4.5 hours, giving a migration rate of about 170 m/hr. Some fish may remain in the upper 100 m as late as 0.5 hour after sunrise, but most probably begin the descent to day depths earlier. A sample made at about 90 m between 1.3 and 0.3 hours before sunrise caught four times as many fish as the following one-hour sample at the same depth, suggesting that a majority of the population begins to migrate within 1.3 hours of sunrise. Daytime depths were reached at least two hours after sunset. This was when the earliest diurnal sample made at day depths ended, so arrival times could have been earlier. Migration time between nocturnal and diurnal depths was, therefore, about 3 hours, yielding a migration rate of 250 m/hr between night and day depths of maximum abundance.
PATCHINESS.—Clumping apparently occurred only at night at each of the three seasons. Clumping was indicated at all three seasons at 51–100 m where, except for juveniles in late spring and adults in late summer, abundance of the three older stages was greatest. The two exceptions were close to the maximum concentration, which was small (Table 42). In late summer clumping was also indicated at 851–900 m, the depth at which nonmigrants were most abundant. There was no indication of a patchy distribution for nonmigrants in winter or late spring.
Other significant CD values were thought to reflect distributional features other than clumping. A significant CD value in late spring at 951–1000 m during the day was due to one of only two positive day samples at that season; one in winter at 601–650 m during the day was due to a sample that probably caught early migrants (see “Vertical Distribution” section).
Night samples from the upper 50 m in late summer and the upper 50 m and 151–200 m in winter also had significant CD values. In late summer only two night samples were taken in the upper 50 m; the one that took fewer fish was made shortly after the crepuscular period, apparently when migrants were just reaching this depth. In winter the CD values obtained for samples taken in the upper 50 m and at 151–200 m may reflect vertical concentration in narrow strata within those depth intervals. In the upper 50 m one fish was taken in three 1-hour samples made at 18 m; none in three 1-hour samples at 34 m; 29 in one 0.6-hour sample at 40 m; and 2 in three 1-hour samples at 50 m. At 151–200 m, three samples each were taken at 175 m and 200 m; all the specimens were caught at 175 m, and neither series, when considered individually, had a significant CD. Year-to-year variation in population size or depth preference may also have contributed to the observed differences. The samples at 175 m were taken in January and those at 200 m in February one year later.
NIGHT:DAY CATCH RATIOS.—Night-to-day catch ratios, including interpolated values, for discrete-depth captures were 0.9:1 in winter, 2.3:1 in late spring, and 2.0:1 in late summer. Juveniles accounted for more than 75 percent of the catch in winter and late summer, and the total ratio in each of the two seasons was similar to that for juveniles (Table 43). Seasonal differences in stage and size composition, abundance, vertical distribution, and depth coverage were all factors in the observed differences in catch rates.
In late spring, when subadults and adults were most abundant, the difference between day and night catches was mostly due to fish 40 mm and larger, suggesting that increased net avoidance by day was the major cause of the observed difference. However, even fish 33–40 mm were more abundant in night samples, suggesting that the day vertical range may not have been adequately sampled.
In late summer 65–70 percent of both day and night catches consisted of fish 16–25 mm. It is not likely that these fish effectively avoided the net, yet they were more than twice as abundant in night samples as in day samples. Fish larger than 39 mm, which presumably have a greater ability to avoid the net than smaller fish, were about equally abundant in day and night samples (2.7 and 3.1 per hour, respectively). Failure to sample a narrow concentration by day may account for most of the difference in catch rates.
The day depth range was poorly sampled in winter, but this was apparently compensated for by interpolated values, which accounted for more than half of the calculated abundance (Table 42). However, a poor estimate of the actual size composition of the population resulted from this technique. Therefore, fish 19–24 mm and fish larger than 50 mm were not accounted for by day.
- bibliographic citation
- Gibbs, Robert H., Jr. and Krueger, William H. 1987. "Biology of midwater fishes of the Bermuda Ocean Acre." Smithsonian Contributions to Zoology. 1-187. https://doi.org/10.5479/si.00810282.452
