Estimating the average distribution of Antarctic krill Euphausia superba at the northern Antarctic Peninsula during austral summer and winter

Summary

This study developed predictive maps showing where Antarctic krill are most likely to be found in the northern Antarctic Peninsula region during summer and winter, filling an important gap needed for ecosystem-based fisheries management.The researchers used acoustic survey data spanning 11 summers (1999-2011) and 4 winters (2012-2016) to identify which environmental conditions are associated with high krill density. They then created spatial models that predict krill distribution across the region.In summer, krill concentrated near the shelf break in warmer, saltier waters with moderate chlorophyll-a levels. During winter, krill were found in shallow waters with low sea-ice concentration and moderate current speeds.These predictive habitat models provide valuable spatial information to support CCAMLR's management approach by identifying areas where krill consistently aggregate in high densities. This information is critical for both sustainable fishing operations and protecting feeding areas that krill-dependent predators like whales, seals, and penguins rely on.

This figure shows the average density of Antarctic krill (Euphausia superba) observed during acoustic surveys. Panel (a) displays mean krill density (shown on a logarithmic scale) averaged across all summer surveys conducted from 1999 to 2011. Panel (b) shows the same data for winter surveys from 2012 to 2016. The maps reveal the spatial distribution patterns of krill concentrations in the northern Antarctic Peninsula region during both seasons.

Key Findings

Summer krill density is highest at shelf breaks, in areas with higher sea surface temperatures, increased salinity, and moderate chlorophyll-a concentrations

Winter krill density is greatest in shallow waters (<1500m), with low sea-ice concentration, moderate sea-level anomaly, and medium current speeds

Krill undergo seasonal migration, with more concentrated distribution in the Bransfield Strait during winter

Predicted summer krill densities are higher than winter densities across the study area

Elevated krill densities were consistently observed near Elephant Island and in nearshore waters along the Antarctic Peninsula and South Shetland Islands

Abstract

This study was performed to aid the management of the fishery for Antarctic krill Euphausia superba. Krill are an important component of the Antarctic marine ecosystem, providing a key food source for many marine predators. Additionally, krill are the target of the largest commercial fishery in the Southern Ocean, for which annual catches have been increasing and concentrating in recent years. The krill fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which has endorsed a new management framework that requires information about the spatial distribution and biomass of krill. Here, we use krill density estimates from acoustic surveys and a GAMM framework to model habitat properties associated with high krill biomass during summer and winter in the northern Antarctic Peninsula region, an area important to the commercial fishery. Our models show elevated krill density associated with the shelf break, increased sea surface temperature, moderate chlorophyll-a concentration and increased salinity. During winter, our models show associations with shallow waters (<1500 m) with low sea-ice concentration, medium sea-level anomaly and medium current speed. Our models predict temporal averages of the distribution and density of krill, which can be used to aid CCAMLR's revised ecosystem approach to fisheries management. Our models have the potential to help in the spatial and temporal design of future acoustic surveys that would preclude the need for modelled extrapolations. We highlight that the ecosystem approach to fisheries management of krill critically depends upon such field observations at relevant spatial and temporal scales.

Published in

Polar Biology

2022

Authors

V. Warwick-Evans, S. Fielding, C. S. Reiss, G. M. Watters, P. N.

Institutions

British Antarctic SurveyAntarctic Ecosystem Research Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, La Jolla

Methods

AcousticData

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