Overwinter habitat selection by Antarctic krill under varying sea-ice conditions: implications for top predators and fishery management

Summary

This study presents the first winter acoustic measurements of Antarctic krill populations around the South Shetland Islands, uncovering striking seasonal movement patterns from deep ocean waters to coastal regions. Krill biomass in Bransfield Strait reached approximately 5.5 million tonnes during winter 2014, roughly ten times higher than typical summer levels. This coastal concentration happened regardless of sea-ice coverage, showing that krill spend winter months in nearshore basins whether or not ice is present. Crabeater seals were found in areas with heavy ice cover and high krill densities, while Antarctic fur seals had more widespread distributions. Climate change is shrinking sea ice in traditional krill habitat areas, potentially increasing competition between fishing operations and predators while changing ecosystem dynamics.

Research area showing sampling locations around the South Shetland Islands (SSI) during winter surveys in 2012 (green cross), 2013 (red dot), and 2014 (green triangle). Boxed areas indicate regions where Antarctic krill population estimates were calculated, including the west shelf (WA), Elephant Island (EI), Bransfield Strait (BS), and Joinville Island (JI) zones. Gerlache Strait (GS) is located in the southwestern-most section of the map.

Key Findings

First winter acoustic population measurements for Antarctic Peninsula krill.

Bransfield Strait winter population: ~5.5 million tonnes (compared to 520,000 tonnes summer average).

Ten-fold increase in krill abundance in coastal waters during winter months.

Krill concentration occurred regardless of sea-ice coverage conditions in 2014.

Crabeater seals gathered in areas with over 70% ice cover and high krill densities.

Antarctic fur seals spread more widely across different ice conditions.

Winter coastal concentration represents 92% of average summer population for entire research area.

Climate change making winter krill concentrations more accessible to fishing operations.

Abstract

Climate change will affect Antarctic krill Euphausia superba, krill-dependent predators, and fisheries in the Southern Ocean as areas typically covered by sea ice become ice-free in some winters. Research cruises conducted around the South Shetland Islands of the Antarctic Peninsula during winters with contrasting ice conditions provide the first acoustic estimates of krill biomass, habitat use, and association with top predators to examine potential interactions with the krill fishery. Krill abundance was very low in offshore waters during all winters. In Bransfield Strait, median krill abundance was an order of magnitude higher (8 krill m⁻²) compared to summer (0.25 krill m⁻²), and this pattern was observed in all winters regardless of ice cover. Acoustic estimates of krill biomass were also an order of magnitude higher (~5 500 000 metric tons [t] in 2014) than a 15 yr summer average (520 000 t).

Published in

Marine Ecology Progress Series

2017

Authors

Reiss, C.S., Cossio, A., Santora, J.A., Dietrich, K.S., Murray, A., Mitchell, B.G., Walsh, J., Weiss, E.L., Gimpel, C., Jones, C.D., Watters, G.M.

Institutions

Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, La JollaDepartment of Applied Mathematics and Statistics, University of California, Santa CruzDesert Research Institute, University of NevadaScripps Institution of Oceanography, University of CaliforniaCenter for Microbial Ecology Research and Education, University of Hawaii

Methods

AcousticDataBiological sampling Field

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