Prey composition and daily rations of myctophid fishes in the Southern Ocean

The feeding ecology of myctophids was studied using data collected during 5 South African scientific cruises to the Southern Ocean from 1985 to 1995. A total of 362 specimens, comprising 36 species, were analyzed for gut contents. Myctophid biomass levels, estimated from Bongo net tows, are among the lowest yet recorded for the Southern Ocean. Peak biomass levels were associated with the main frontal zones and with a permanent polynya region in the Lazarev Sea. Results show that all myctophid species are opportunistic mesozooplankton feeders exhibiting a high degree of overlap in their food spectrum and consuming primarily the most abundant species of copepods, euphausiids, hyperiids and pteropods. Daily rations were estimated using 3 different approaches and ranged from 0.2 to 4.4% of dry body weights. Generally, the daily food intake was equivalent to 0.5 (lower mean) to 2.9 (upper mean) of dry body weight for Antarctic and subantarctic species, and between 1.2 and 3.8% for temperate and subtropical species. Antarctic krill, Euphausia superba, was usually poorly represented in the stomachs of all but 1 myctophid species. The results of this study therefore do not support the hypothesis that krill plays a major role in the feeding ecology and budget of myctophids.