SOME ASPECTS OF THE ECOLOGY OF LANTERNFISHES 

 (MYCTOPHIDAE) IN THE PACIFIC OCEAN NEAR HAWAII 



Thomas A. Clarke' 



ABSTRACT 



Most species of myctophids collected near Hawaii showed ontogenetic differences in vertical 

 distribution and migration. Newly transformed juveniles of several species did not regularly 

 migrate. Within both day and night depth ranges, the smaller fish tended to occur shallower 

 than the adults. Few differences were related to sex or reproductive condition. Large 

 fractions of populations of three species appeared not to migrate at certain seasons. Seasonal 

 changes in size composition of populations and ripeness of mature females indicated that 

 most abundant species spawn principally in the spring and summer and live about I year. 

 The size-depth patterns of congeners and closely related species were quite different, while 

 similar-sized individuals of dissimilar species tended to co-occur at the same depths. 



Comparison of day and night estimates of abundance and size composition indicated 

 that there was little differential avoidance by most species. There were differences between 

 catches by a 10-ft Isaacs-Kidd trawl and a modified Cobb pelagic trawl related to 

 both species and size with neither trawl showing a distinct advantage for all species. Com- 

 parison of catches at full and new moon indicated that at full moon most species occurred 

 about 30 m deeper and avoided the Isaacs-Kidd trawl better than at new moon. 



The average standing crop of myctophids was about 0.32 g(wet weight)/m-, and the 

 yearly turnover rate was estimated at roughly twice the standing crop. Myctophids and 

 other vertically migrating micronekton appear to be very important in the trophic structure 

 of the tropical open ocean and probably account for most of the consumption of 

 zooplankton. 



Myctophids or lanternfishes are one of the 

 dominant families of mesopelagic fishes and are 

 generally thought to be important in the open 

 ocean ecosystem because of their frequent 

 occurrence and apparently great abundances. 

 The bulk of early work was concerned primarily 

 with taxonomy and distribution. Most recent 

 work has concentrated on one aspect of their 

 ecology, diurnal vertical migration. Myctophids 

 have been shown in a number of cases, e.g., 

 Paxton (1967), Badcock (1970), to undertake 

 substantial migrations from depths of several 

 hundred meters during the day to the upper 

 100-200 m at night, but few studies have done 

 more than describe the vertical distribution 

 patterns and suggest possible relationships of 

 these to gradients in temperature or light with 

 depth or with the position of sonic scattering 

 layers. There are numerous gaps in our knowl- 



' Hawaii Institute of Marine Biology and Department 

 of Oceanography, University of Hawaii, Honolulu, HI 

 96822. 



edge of other aspects of the ecology of this 

 ubiquitous group of fishes. Moreover, previous 

 work has not been equitably distributed in a 

 geographic sense; most has been carried out at 

 higher latitudes. 



Among others, Badcock (1970) has indicated 

 that there are size-specific differences in migra- 

 tion patterns of some species of myctophids, but 

 ontogenetic changes in depth distribution have 

 not been studied quantitatively. Similarly, 

 Nafpaktitis (1968) has indicated that in some 

 species of the genus Diap}u(i< the mature females 

 do not migrate. It is not known whether either 

 of these patterns is typical or widespread within 

 the family. Extensive life history data have been 

 presented for some abundant northern species, 

 Benthosoma glaciale (Halliday, 1970), Ste)io- 

 branchus leucopsaurus (Smoker and Pearcy, 

 1970), and Mijctophum affine (Odate, 1966), but 

 the life histories of most species, particularly 

 tropical ones, remain unknown. 



This paper presents and discusses data on 

 myctophids collected in several series of mid- 



Manuscript accepted November 1972. 

 FISHERY BULLETIN: VOL. 71, NO. 2, 1973. 



401 



