Classification of Southern Ocean krill and icefish echoes using random forests
Abstract Target identification remains a challenge for acoustic surveys of marine fauna. Antarctic krill, Euphausia superba, are typically identified through a combination of expert scrutiny of echograms and analysis of differences in mean volume backscattering strengths (SV; dB re 1 m−1) measured a...
Published in: | ICES Journal of Marine Science |
---|---|
Main Authors: | , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Oxford University Press (OUP)
2016
|
Subjects: | |
Online Access: | http://dx.doi.org/10.1093/icesjms/fsw057 http://academic.oup.com/icesjms/article-pdf/73/8/1998/31230755/fsw057.pdf |
id |
croxfordunivpr:10.1093/icesjms/fsw057 |
---|---|
record_format |
openpolar |
spelling |
croxfordunivpr:10.1093/icesjms/fsw057 2024-05-12T07:55:15+00:00 Classification of Southern Ocean krill and icefish echoes using random forests Fallon, Niall G. Fielding, Sophie Fernandes, Paul G. 2016 http://dx.doi.org/10.1093/icesjms/fsw057 http://academic.oup.com/icesjms/article-pdf/73/8/1998/31230755/fsw057.pdf en eng Oxford University Press (OUP) ICES Journal of Marine Science volume 73, issue 8, page 1998-2008 ISSN 1095-9289 1054-3139 Ecology Aquatic Science Ecology, Evolution, Behavior and Systematics Oceanography journal-article 2016 croxfordunivpr https://doi.org/10.1093/icesjms/fsw057 2024-04-18T08:16:20Z Abstract Target identification remains a challenge for acoustic surveys of marine fauna. Antarctic krill, Euphausia superba, are typically identified through a combination of expert scrutiny of echograms and analysis of differences in mean volume backscattering strengths (SV; dB re 1 m−1) measured at two or more echosounder frequencies. For commonly used frequencies, however, the differences for krill are similar to those for many co-occurring fish species that do not possess swimbladders. At South Georgia, South Atlantic, one species in particular, mackerel icefish, Champsocephalus gunnari, forms pelagic aggregations, which can be difficult to distinguish acoustically from large krill layers. Mackerel icefish are currently surveyed using bottom-trawls, but the resultant estimates of abundance may be biased because of the species' semi-pelagic distribution. An acoustic estimate of the pelagic component of the population could indicate the magnitude of this bias, but first a reliable target identification method is required. To address this, random forests (RFs) were generated using acoustic and net sample data collected during surveys. The final RF classified as krill, icefish, and mixed aggregations of weak scattering fish species with an overall estimated accuracy of 95%. Minimum SV, mean aggregation depth (m), mean distance from the seabed (m), and geographic positional data were most important to the accuracy of the RF. Time-of-day and the difference between SV at 120 kHz (SV 120) and that at 38 kHz (SV 38) were also important. The RF classification resulted in significantly higher estimates of backscatter apportioned to krill when compared with widely applied identification methods based on fixed and variable ranges of SV 120–SV 38. These results suggest that krill density is underestimated when those SV-differencing methods are used for target identification. RFs are an objective means for target identification and could enhance the utility of incidentally collected acoustic data. Article in Journal/Newspaper Antarc* Antarctic Antarctic Krill Euphausia superba Icefish Southern Ocean Oxford University Press Antarctic Southern Ocean ICES Journal of Marine Science 73 8 1998 2008 |
institution |
Open Polar |
collection |
Oxford University Press |
op_collection_id |
croxfordunivpr |
language |
English |
topic |
Ecology Aquatic Science Ecology, Evolution, Behavior and Systematics Oceanography |
spellingShingle |
Ecology Aquatic Science Ecology, Evolution, Behavior and Systematics Oceanography Fallon, Niall G. Fielding, Sophie Fernandes, Paul G. Classification of Southern Ocean krill and icefish echoes using random forests |
topic_facet |
Ecology Aquatic Science Ecology, Evolution, Behavior and Systematics Oceanography |
description |
Abstract Target identification remains a challenge for acoustic surveys of marine fauna. Antarctic krill, Euphausia superba, are typically identified through a combination of expert scrutiny of echograms and analysis of differences in mean volume backscattering strengths (SV; dB re 1 m−1) measured at two or more echosounder frequencies. For commonly used frequencies, however, the differences for krill are similar to those for many co-occurring fish species that do not possess swimbladders. At South Georgia, South Atlantic, one species in particular, mackerel icefish, Champsocephalus gunnari, forms pelagic aggregations, which can be difficult to distinguish acoustically from large krill layers. Mackerel icefish are currently surveyed using bottom-trawls, but the resultant estimates of abundance may be biased because of the species' semi-pelagic distribution. An acoustic estimate of the pelagic component of the population could indicate the magnitude of this bias, but first a reliable target identification method is required. To address this, random forests (RFs) were generated using acoustic and net sample data collected during surveys. The final RF classified as krill, icefish, and mixed aggregations of weak scattering fish species with an overall estimated accuracy of 95%. Minimum SV, mean aggregation depth (m), mean distance from the seabed (m), and geographic positional data were most important to the accuracy of the RF. Time-of-day and the difference between SV at 120 kHz (SV 120) and that at 38 kHz (SV 38) were also important. The RF classification resulted in significantly higher estimates of backscatter apportioned to krill when compared with widely applied identification methods based on fixed and variable ranges of SV 120–SV 38. These results suggest that krill density is underestimated when those SV-differencing methods are used for target identification. RFs are an objective means for target identification and could enhance the utility of incidentally collected acoustic data. |
format |
Article in Journal/Newspaper |
author |
Fallon, Niall G. Fielding, Sophie Fernandes, Paul G. |
author_facet |
Fallon, Niall G. Fielding, Sophie Fernandes, Paul G. |
author_sort |
Fallon, Niall G. |
title |
Classification of Southern Ocean krill and icefish echoes using random forests |
title_short |
Classification of Southern Ocean krill and icefish echoes using random forests |
title_full |
Classification of Southern Ocean krill and icefish echoes using random forests |
title_fullStr |
Classification of Southern Ocean krill and icefish echoes using random forests |
title_full_unstemmed |
Classification of Southern Ocean krill and icefish echoes using random forests |
title_sort |
classification of southern ocean krill and icefish echoes using random forests |
publisher |
Oxford University Press (OUP) |
publishDate |
2016 |
url |
http://dx.doi.org/10.1093/icesjms/fsw057 http://academic.oup.com/icesjms/article-pdf/73/8/1998/31230755/fsw057.pdf |
geographic |
Antarctic Southern Ocean |
geographic_facet |
Antarctic Southern Ocean |
genre |
Antarc* Antarctic Antarctic Krill Euphausia superba Icefish Southern Ocean |
genre_facet |
Antarc* Antarctic Antarctic Krill Euphausia superba Icefish Southern Ocean |
op_source |
ICES Journal of Marine Science volume 73, issue 8, page 1998-2008 ISSN 1095-9289 1054-3139 |
op_doi |
https://doi.org/10.1093/icesjms/fsw057 |
container_title |
ICES Journal of Marine Science |
container_volume |
73 |
container_issue |
8 |
container_start_page |
1998 |
op_container_end_page |
2008 |
_version_ |
1798835016986263552 |