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A mass stranding, or `walk out' of west coast rock lobster, Jasus lalandii, in Elands Bay, South Africa: Causes, results, and implications

Biomedical Sciences Research Institute Computer Science Research Institute Environmental Sciences Research Institute Nanotechnology & Advanced Materials Research Institute

Cockcroft, AC, Schoeman, DS, Pitcher, GC, Bailey, GW and Van Zyl, DL (2000) A mass stranding, or `walk out' of west coast rock lobster, Jasus lalandii, in Elands Bay, South Africa: Causes, results, and implications. In: BIODIVERSITY CRISIS AND CRUSTACEA. (Eds: von Vaupel Klein, J and Schram, FR), A.A. Balkema, pp. 673-688. ISBN 90-5410-478-3 [Book section]

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Abstract

During 14 March-7 May, 1997, South Africa experienced its worst ever low-oxygen induced rock lobster mortality. About 2000 tons (compared to an annual TAC of 1,680 tons for the 1996/97 season) of Jasus lalandii were stranded in and around Elands Bay, an important fishing area on the west coast of South Africa. The persistent accumulation and eventual decay of a dense dinoflagellate bloom (most likely as a result of nutrient depletion) and concomitant depletion of oxygen, as a result of aerobic bacterial activity, was the cause of the low oxygen levels that precipitated the sequence of stranding events. A massive stranding of some 1,500 tons in Elands Bay during 5-8 April (spring tides) was preceded by two large strandings and followed by three less severe events. This sequence followed a general north-south progression. Females constituted the bulk (about 80%) of the stranded lobster up to early April, with males increasing in importance during the latter events. The proportion of stranded lobster larger than the commercial minimum size limit (75 mm CL) increased from < 20%, during 14 March-25 April, to around 30% for the last two stranding events. In total, some 318 tons (16% of total lobster stranded during the sequence of events) were returned to the sea alive in areas unaffected by low oxygen. Trap and diving surveys conducted after the strandings illustrated the success of this operation. These surveys, together with decreased commercial catch per unit effort in the area, indicated that lobster distribution, but not abundance, recovered within a year of the strandings. Decreased lobster growth rates were also noted in the season following the strandings. The long-term implications of this substantial loss (5-10% of total spawning biomass) to the resource as a whole are difficult to assess. Since the recruitment dynamics of this species are poorly understood at present, and recruitment to the fished population requires in excess of six years, the full impact of this event may only be manifested in the future.

Item Type:Book section
Faculties and Schools:Faculty of Life and Health Sciences
Faculty of Life and Health Sciences > School of Environmental Sciences
Research Institutes and Groups:Environmental Sciences Research Institute
Environmental Sciences Research Institute > Coastal Systems
ID Code:480
Deposited By:Dr David Schoeman
Deposited On:09 Mar 2010 14:23
Last Modified:28 Mar 2012 16:20

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