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

AC Cockcroft, DS Schoeman, GC Pitcher, GW Bailey, DL Van Zyl

    Research output: Chapter in Book/Report/Conference proceedingChapter

    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.
    Original languageEnglish
    Title of host publicationBIODIVERSITY CRISIS AND CRUSTACEA
    EditorsJ von Vaupel Klein, FR Schram
    PublisherTaylor & Francis
    Pages673-688
    Volume12
    ISBN (Print)90-5410-478-3
    Publication statusPublished - 2000

    Publication series

    NameCRUSTACEAN ISSUES
    PublisherA.A. Balkema

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    Cockcroft, AC., Schoeman, DS., Pitcher, GC., Bailey, GW., & 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 J. von Vaupel Klein, & FR. Schram (Eds.), BIODIVERSITY CRISIS AND CRUSTACEA (Vol. 12, pp. 673-688). (CRUSTACEAN ISSUES). Taylor & Francis.