Variation in the biomass density and demography of Antarctic krill in the vicinity of the South Shetland Islands during the 1999/2000 austral summer

Interannual spatial variability of krill (Euphausia superba) influences seabird foraging behavior near Elephant Island, Antarctica

“…They found that the areas of highest krill density shift toward the shelf break as the season progressed. They also found that changes in density and dispersion patterns reflected shifts of adult (∼50 mm) and juvenile (∼25 mm) krill, where sexually advanced stages of krill immigrated into the region later in the season and displaced juvenile stages (Hewitt et al. , 2004c).…”

“…Land‐based krill predators breeding on the South Shetland Islands consume ∼0.83 million tons of krill during the reproductive season (Croll and Tershy, 1998). The krill fishery that operated near the South Shetland Islands and Elephant Island during the 1980s and 1990s targeted krill patches within <100 km of penguin and petrel colonies during their breeding periods (Agnew and Phegan, 1995; Marin and Delgado, 2001), so while the total catch was not great (100 kTons) the distribution of the fishing effort is of great concern (Hewitt et al. , 2004c).…”

“…, 2004b; Demer and Conti, 2005). Fishery removals over the last 10 yr have averaged ∼100 kTons, with most of this occurring around the South Shetland Islands and near South Georgia and within 50 nautical miles (nmi) of breeding colonies (Hewitt et al. , 2004c).…”

“…Pulses were transmitted every 2 s at 1 kW for 1 ms. Positions were logged every 2 s. SonarData Echoview was used to aggregate acoustic data into 1‐nmi horizontal intervals and to a depth of 200 m. We use the nautical area scattering coefficient (NASC) as an index of krill and zooplankton abundance (log # nmi −1 ) (Hewitt and Demer, 1993; Madureira et al. , 1993; Hewitt et al. , 2004a,b,c;Demer and Conti, 2005).…”

“…Current biomass estimates for the Scotia Sea range between 40 and 100 million tons (Hewitt et al, 2004b;Demer and Conti, 2005). Fishery removals over the last 10 yr have averaged 100 kTons, with most of this occurring around the South Shetland Islands and near South Georgia and within 50 nautical miles (nmi) of breeding colonies (Hewitt et al, 2004c). Near Elephant Island, krill biomass fluctuates with a period of roughly 8 yr (Hewitt et al, 2003) and successful reproduction and recruitment by krill is related to the extent of sea ice (Loeb et al, 1997).…”