Biomass Measures Assessment of Antarctic Krill

LOGO THAROSGood day Friends and Colleagues.

The Antarctic Marine Living Resources program of the NOAA Southwest Fisheries Science Center’s Antarctic Ecosystem Research Division has been conducing research surveys of Antarctic krill (Euphausa superba) around the Antarctic peninsula since the late 1980s.

The surveys expanded during this period from a grid of net tows around Elephant Island to four grids including adjacent regions, with acoustic biomass measured along transect lines between the stations. Two legs a month apart were generally sampled, but not every station or area was sampled every year.

Main conclusions are that:

  • Krill annual biomass calculated based on net tows was usually less than the biomass produced by acoustics, and was uncorrelated with the acoustic values over a 19 year period.
  • The assessment model is able to fit both data series by using differences in age selectivity.
  • Krill spawning biomass in the integrated model using only the acoustic biomass data was about twice the spawning biomass based on only the net trawls for most years.
  • Heavier weightings on biomass from acoustics produced larger estimates of spawning biomass than when the biomass from net trawls were weighted more heavily.

Detailed report seen here.