Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa
The migration of Southern Hemisphere humpback whales Megaptera novaeangliae between their feeding and breeding areas has thus far been considered a highly predictable and seasonal event. However, previous observations on the humpbacks that pass through the nearshore waters of the west coast of South...
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ftjafricanj:oai:ojs.ajol.info:article/54596 2023-05-15T16:36:08+02:00 Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa Barendse, J Best, PB Thornton, M Pomilla, C Carvalho, I Rosenbaum, HC 2010-05-20 application/pdf http://www.ajol.info/index.php/ajms/article/view/54596 eng eng NISC http://www.ajol.info/index.php/ajms/article/view/54596/62568 http://www.ajol.info/index.php/ajms/article/downloadSuppFile/54596/74 http://www.ajol.info/index.php/ajms/article/view/54596 Copyright for articles published in this journal is retained by the publisher. African Journal of Marine Science; Vol 32, No 1 (2010); 1-22 1814-232X info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Peer-reviewed Article 2010 ftjafricanj 2017-03-05T06:34:25Z The migration of Southern Hemisphere humpback whales Megaptera novaeangliae between their feeding and breeding areas has thus far been considered a highly predictable and seasonal event. However, previous observations on the humpbacks that pass through the nearshore waters of the west coast of South Africa have revealed deviations from the behaviour and seasonality expected during a typical migration. This ‘anomaly’ is hypothesised to be associated with prey availability in the region. Shore-based observations between July 2001 and February 2003 from North Head, Saldanha Bay, in the Western Cape province, yielded relative abundances that again did not support a classical migration pattern, with the highest sighting rates from mid-spring through summer. Movement parameters (actual swimming speed, direction and linearity) of humpback groups tracked by theodolite showed mid-spring to be a turning point in their behaviour, after which we observed a significant reduction in actual swimming speed, an increase in ‘non-directional’ movement, and a distribution farther from shore than in other seasons. Additional data on group composition and sex collected between 1993 and 2008 showed a significantly female-biased sex ratio during mid-spring, the first such recorded for any region. Direct observation of feeding on crustacean prey during spring and summer further supports the notion that humpbacks may have more flexible foraging habits than previously appreciated, and that the southern Benguela upwelling region may function as an important feeding area for these whales. Keywords: Benguela upwelling; Breeding Stock B; feeding; group composition; humpback whale; migration; Pythagoras software; seasonality; sex ratios; shore-based survey; South Atlantic; theodolite trackingAfrican Journal of Marine Science 2010, 32(1): 1–22 Article in Journal/Newspaper Humpback Whale Megaptera novaeangliae AJOL - African Journals Online |
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Open Polar |
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AJOL - African Journals Online |
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ftjafricanj |
language |
English |
description |
The migration of Southern Hemisphere humpback whales Megaptera novaeangliae between their feeding and breeding areas has thus far been considered a highly predictable and seasonal event. However, previous observations on the humpbacks that pass through the nearshore waters of the west coast of South Africa have revealed deviations from the behaviour and seasonality expected during a typical migration. This ‘anomaly’ is hypothesised to be associated with prey availability in the region. Shore-based observations between July 2001 and February 2003 from North Head, Saldanha Bay, in the Western Cape province, yielded relative abundances that again did not support a classical migration pattern, with the highest sighting rates from mid-spring through summer. Movement parameters (actual swimming speed, direction and linearity) of humpback groups tracked by theodolite showed mid-spring to be a turning point in their behaviour, after which we observed a significant reduction in actual swimming speed, an increase in ‘non-directional’ movement, and a distribution farther from shore than in other seasons. Additional data on group composition and sex collected between 1993 and 2008 showed a significantly female-biased sex ratio during mid-spring, the first such recorded for any region. Direct observation of feeding on crustacean prey during spring and summer further supports the notion that humpbacks may have more flexible foraging habits than previously appreciated, and that the southern Benguela upwelling region may function as an important feeding area for these whales. Keywords: Benguela upwelling; Breeding Stock B; feeding; group composition; humpback whale; migration; Pythagoras software; seasonality; sex ratios; shore-based survey; South Atlantic; theodolite trackingAfrican Journal of Marine Science 2010, 32(1): 1–22 |
format |
Article in Journal/Newspaper |
author |
Barendse, J Best, PB Thornton, M Pomilla, C Carvalho, I Rosenbaum, HC |
spellingShingle |
Barendse, J Best, PB Thornton, M Pomilla, C Carvalho, I Rosenbaum, HC Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
author_facet |
Barendse, J Best, PB Thornton, M Pomilla, C Carvalho, I Rosenbaum, HC |
author_sort |
Barendse, J |
title |
Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
title_short |
Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
title_full |
Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
title_fullStr |
Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
title_full_unstemmed |
Migration redefined? Seasonality, movements and group composition of humpback whales Megaptera novaeangliae off the west coast of South Africa |
title_sort |
migration redefined? seasonality, movements and group composition of humpback whales megaptera novaeangliae off the west coast of south africa |
publisher |
NISC |
publishDate |
2010 |
url |
http://www.ajol.info/index.php/ajms/article/view/54596 |
genre |
Humpback Whale Megaptera novaeangliae |
genre_facet |
Humpback Whale Megaptera novaeangliae |
op_source |
African Journal of Marine Science; Vol 32, No 1 (2010); 1-22 1814-232X |
op_relation |
http://www.ajol.info/index.php/ajms/article/view/54596/62568 http://www.ajol.info/index.php/ajms/article/downloadSuppFile/54596/74 http://www.ajol.info/index.php/ajms/article/view/54596 |
op_rights |
Copyright for articles published in this journal is retained by the publisher. |
_version_ |
1766026433712357376 |