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 migr<jte 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 IO-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 50 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 2 , 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.

Gunter R. Seckel

Papers

Vertical Sections of Temperature and Salinity in the Trade Wind Zone of the Central North Pacific, February 1964 to June 1965