CLARKE: ECOLOGY OF LANTERNFISHES 



Table 4. — Proportion of females among total mature fish at different seasons 

 for 10 species of myctophids. Total number examined is given in parentheses. 



that the same or equivalent populations were 

 sampled on each cruise. Possible changes due 

 to horizontal advective transport were ignored. 

 Advection rates, especially for organisms which 

 spend one-half of their time below the surface 

 layers, and horizontal gradients in the parame- 

 ters measured — abundance, size composition, 

 etc. — are probably low. It seems unlikely that 

 populations which had been subjected to greatly 

 different environmental conditions were advected 

 into the study during the periods between 

 cruises. 



The most likely possibility of change due to 

 advection would be related to seasonal north- 

 south shifts of water masses. Near Hawaii in 

 the upper layers, water transitional between 

 North Pacific Central and North Pacific Equa- 

 torial displaces North Pacific Central water 

 during the summer. This shift is known to affect 

 the abundance of skipjack tuna (Seckel, 1969). 



The absence of marked changes in species 

 composition and relative abundance of the 

 myctophid fauna suggest that north-south 

 shifts of water masses did not, during the study 

 period, markedly affect populations. Two 

 examples illustrate this particularly well. 

 DiapIiKs schmidti, a species of myctophid which 

 apparently does not occur much further south 

 than Hawaii, was consistently taken here in 

 abundance, while a very similar congener, 

 D. gannaiuii, which is very abundant from at 

 least lat. 12°30'N and further south (Hartmann, 

 1971), was never taken. Two species, Dio- 

 geiiichthys atlanticus and Diaphns fragUis, 

 which are very abundant in equatorial waters 

 (Hartmann, 1971), were taken consistently 

 but never in great numbers near Hawaii. 



Most species that showed seasonal changes in 



size composition appeared to reach maturity 

 in about 1 year. The larger species — Lanipadoia 

 spp., Lampanyctus itobilia, Boli)iichthys supnt- 

 lateralii^, and Notoscopelus caudispi^iosus — 

 probably take longer. In many species the 

 adults nearly or completely disappeared at 

 about the same time that juveniles became 

 most abundant suggesting that few individuals 

 live longer than 1 year. 



The ages at maturity and life spans of colder 

 water species of myctophids, e.g., Benthosema 

 glaciale (Halliday, 1970), Stenobranchus 

 leucopsaurus (Smoker and Pearcy, 1970), are 

 considerably greater than those suggested here 

 for tropical species. Murphy (1968) has pre- 

 sented data on epipelagic clupeoid fishes which 

 show a marked decrease in age at maturity, the 

 number of reproductions, and life span related 

 to year-to-year variability in spawning success. 

 He suggests that the latter is directly related 

 to year-to-year variability in the physical 

 environment. It is not unreasonable that the 

 same trend exists for a mesopelagic family 

 that occurs in both variable high-latitude 

 waters and in the more stable tropical open 

 ocean. 



Most species appear to spawn predominately 

 in the spring or summer. Primary production 

 measurements taken by S. A. Cattell near 

 Hawaii during 1969-70 indicate that primary 

 production and productivity index are much 

 higher during March-June than the period 

 from October to January. Zooplankton pro- 

 duction probably lags behind the peaks in 

 primary production only slightly. Assuming 

 that this seasonal pattern recurred during the 

 present study, the period of principal spawning 

 for most myctophid species appears to be timed 



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