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    A hypothetical life cycle for Antarctic toothfish Dissostichus mawsoni in Antarctic waters of CCAMLR Statistical Area 88

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    S.M. Hanchet, G.J. Rickard, J.M. Fenaughty, A. Dunn and M.J. Williams (New Zealand)
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    Aspects of the reproduction, size distribution, and movements of Antarctic toothfish Dissostichus mawsoni in CCAMLR Statistical Areas 88.1 & 88.2 were reviewed. Based on the presumed location and timing of spawning, and the probable early life history characteristics of toothfish, we investigated models that mimic the drift of eggs and larvae over a 6–24 month period using an oceanic circulation model linked to the high resolution global environmental model (HiGEM). The location of toothfish larvae after an 18–24 month period suggested by the models agreed moderately well with the distribution of the smallest toothfish taken in the toothfish fishery.
    Our present hypothesis is that D. mawsoni in CCAMLR Statistical Subareas 88.1 and 88.2 spawn to the north of the Antarctic continental slope, mainly on the ridges and banks of the Pacific-Antarctic Ridge. The spawning appears to take place during winter and spring, and may extend over a period of several months. Depending on the exact location of spawning, eggs and larvae become entrained by the Ross Sea gyres, and may either move west settling out around the Balleny Islands and adjacent Antarctic continental shelf, south onto the Ross Sea shelf, or eastwards with the eastern Ross Sea gyre settling out along the continental slope and shelf to the east of the Ross Sea in Subarea 88.2. As the juveniles grow in size they move west back towards the Ross Sea shelf and then move out into deeper water (greater than 600m). The fish gradually move northwards as they mature, feeding in the slope region in depths of 1000–1500 m, where they gain condition before moving north onto the Pacific-Antarctic ridge to start the cycle again. Spawning fish may remain in the northern area for up to 2–3 years. They then move southwards back onto the shelf and slope where productivity is higher and food is more plentiful where they regain condition before spawning.
    We recommend research surveys be carefully planned to test some of these hypotheses.