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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on July 7, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(9):1967-1971; doi:10.1093/icesjms/fsp198
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Bottom temperature and in situ development of chokka squid eggs (Loligo vulgaris reynaudii) on mid-shelf spawning grounds, South Africa

Anè Oosthuizen1 and Mike J. Roberts2

1 Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown, South Africa. Present address: South African National Parks, PO Box 20419, Humewood, 6013 Port Elizabeth, South Africa
2 Marine and Coastal Management, Private Bag X2, Rogge Bay 8012, South Africa

Correspondence to A. Oosthuizen: tel: +27 83 5408500; fax +27 41 5085415; e-mail: ane.oosthuizen{at}nmmu.ac.za

Oosthuizen, A., and Roberts, M. J. 2009. Bottom temperature and in situ development of chokka squid eggs (Loligo vulgaris reynaudii) on mid-shelf spawning grounds, South Africa. – ICES Journal of Marine Science, 66: 1967–1971.

The aim of the study was to test the development success of squid eggs on the mid-shelf (60–150 m deep) spawning grounds in relation to previous laboratory results, and to describe the mid-shelf temperature environment and how it could affect egg development. A series of in situ egg incubation experiments was conducted on the mid-shelf (~119 m deep) spawning grounds using cages, temperature sensors, and acoustic releases for retrieval. Newly spawned eggs were collected by scuba, and continuous temperature data were collected at two points between the known inshore spawning grounds and the mid-shelf areas. Temperature variations followed a seasonal warming and cooling cycle, with superimposed peaks and troughs. Egg development data indicated that warm temperature peaks (10–13°C) are sufficient for normal development of eggs on the mid-shelf. Egg development time on the mid-shelf was 2–3 times longer (50–60 vs. 20–30 d) than inshore. The scarcity of abnormalities (0.45%) disputes previous laboratory results that suggested that ~50% of eggs would suffer abnormalities in the colder mid-shelf temperature environment.

Keywords: Agulhas Bank, chokka squid, downwelling, egg development, spawning, temperature

Received 31 October 2007; accepted 12 June 2009; advance access publication 7 July 2009.


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