Issue |
Aquat. Living Resour.
Volume 16, Number 3, July 2003
Acoustics in Fisheries and Aquatic Ecology. Part 2
|
|
---|---|---|
Page(s) | 205 - 213 | |
DOI | https://doi.org/10.1016/S0990-7440(03)00019-6 | |
Published online | 15 July 2003 |
An 8-year cycle in krill biomass density inferred from acoustic surveys conducted in the vicinity of the South Shetland Islands during the austral summers of 1991–1992 through 2001–2002
Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92037, USA
Corresponding author: rhewitt@ucsd.edu
Accepted: 7 January 2003
Data from single and multi-frequency active acoustic surveys conducted annually in the vicinity of the South Shetland Islands, Antarctica were re-analyzed using updated procedures for delineating volume backscattering due to Antarctic krill, adjusting for signal contamination due to noise, and compensating for diel vertical migration of krill outside of the acoustic observation window. Intra-and inter-seasonal variations in krill biomass density and dispersion were derived from the re-processed data set for surveys conducted in the austral summers of 1991/1992 through 2001/2002. Estimated biomass density ranged from 1 to 60 g m–2, decreasing from mid-range levels in 1991/1992 to a minimum in 1992/1993–1993/1994, increasing to a peak in 1996/1997–1997/1998, and decreasing again through 2000/2001–2001/2002. Although this variability may be attributed to changes in the spatial distribution of krill relative to the survey area, comparisons with the proportion of juvenile krill in simultaneous net samples suggest that the changes in biomass density are consistent with apparent changes in reproductive success. A truncated Fourier series fit to the biomass density time series is dominated by an 8-year cycle and predicts an increase in krill biomass density in 2002/2003 and 2003/2004. This prediction is supported by an apparent association between cycles in the extent of sea ice cover and per-capita krill recruitment over the last 23 years and indications that ice cover in the winter of 2002 is seasonally early and extensive.
Key words: Krill / Antarctica / South Shetland Islands
© Elsevier, IRD, Inra, Ifremer, Cemagref, 2003
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.