CLARKE: ECOLOGY OF LANTERNFISHES 



high values for Triphoturus nigrescens and 

 Lampariyctus niger, and the peak in total 

 biomass then was caused mainly by the larger 

 numbers of L. niger, a large species, and the 

 fact that Ceratoscopelus ivar))U)igi had the 

 highest percentage of adults at this time. Over- 

 all, C. war'mi)igi and L. )iige7^ were clearly the 

 dominant species with respect to both numbers 

 and biomass. 



The average number of myctophids per m- 

 was about 0.55 and the average biomass was 

 about 0.32 gim'-. These figures are lower than 

 those given by Pearcy and Laurs (1966) for 

 total mesopelagic fishes in the upper 1,000 m 

 off Oregon — 1.5 individuals and 3.6 g/m- for 

 the night tows. The total number of the three 

 dominant myctophids off Oregon was about 

 0.78/m'. Analyses of other fishes collected off 

 Hawaii is not yet complete, but inclusion of 

 other groups, particularly the hatchetfishes, 

 Cyclothone, and larger stomiatoids would likely 

 raise the average number and possibly the 

 average biomass to values comparable to those 

 of Pearcy and Laurs. 



Preliminary analyses of the biomass of 

 other groups of micronekton indicate that most 

 of the biomass in the upper 250 m at night is in 

 the form of vertically migrating groups which 

 are not present during the day and that the 

 myctophids dominate the fauna as a whole. The 

 only other important group of vertically 

 migrating fishes were the gonostomatids whose 

 biomass, principally from Gonostoma spp., was 

 about one-fourth that of the myctophids. The 

 myctophid biomass was one to two times that 

 of the caridean shrimps and about one to four 

 times that of the larger euphausiids, TJuji^anopo- 

 da spp. 



The biomass of epipelagic fishes and larval 

 fishes over 10 mm was about one-sixth that of 

 the myctophids. The figure for epipelagic fishes 

 may be low due to higher concentrations very 

 near the surface, where the sampling was 

 inadequate, and possibly greater avoidance. In 

 general, however, the data agree with Ahlstrom's 

 (1969) conclusions, based on abundances of 

 larval fishes, that vertically migrating, meso- 

 pelagic groups — principally myctophids and 

 gonostomatids — dominate the open ocean fish 

 fauna. 



Conservatively, the average biomass of 

 micronekton is at least three times that of the 

 myctophids or about 1.0 g/m-. Most myctophids 

 appear to have a 1-year life cycle, and in many 

 species, the population is nearly totally replaced 

 by each new generation. The difference between 

 the highest and lowest estimates of myctophid 

 biomass is greater than the average value. 

 Yearly production is then probably higher than 

 the average standing crop. It is not unreasonable 

 to assume that the dynamics of other groups of 

 micronekton are similar and that micronekton 

 production is about twice the average standing 

 crop. 



If, following Ryther (1969), it is assumed 

 that ecological efficiency in the open ocean is 

 about 10% for each trophic level and the 

 organisms are about 10% carbon, then a pro- 

 duction of 0.2 g C/m- by the micronekton 

 would require production of 2 g C/m-/yr by 

 the trophic level below. The yearly primary 

 production in this area is about 50 g C/m-/yr 

 (S. A. Cattell, pers. comm.) with about 5 g 

 C/m-/yr available to the third trophic level 

 and 0.5 g C/m-/yr to the fourth. For the rather 

 conservative estimate of micronekton produc- 

 tion to result, ecological efficiencies must be 

 higher than 10% or the food chain in the open 

 ocean must be shorter than generally assumed 

 by Ryther (1969) and others, i.e., the micronek- 

 ton must be consuming a large fraction of 

 production by herbivores. 



A final point concerns the fate of micronekton 

 production; about 2 g/m-/yr must be consumed 

 by higher carnivores. Studies of the feeding 

 habits of such predators as tuna; dolphin, 

 Coi^phaena; and lancet fish, Alepisai(rus 

 (Gibbs and Collette, 1959; King and Iversen. 

 1962; Haedrich and Nielsen, 1966; Fourmanoir, 

 1971) indicate that these predators consume 

 few vertically migrating forms such as 

 myctophids or gonostomatids. Tuna and dolphin 

 appear to eat mostly epipelagic forms. Unless 

 the standing crop of epipelagic micronekton 

 has been greatly underestimated here or its 

 turnover rate is greater than that of vertically 

 migrating forms, the "typical" predators of the 

 open ocean are consuming only a fraction of the 

 production by micronekton. In order to identify 

 the principal energy pathways in the open 



431 



