A hypothetical life cycle for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region
Aspects of the reproduction, size distribution and movements of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region are reviewed. Based on the presumed location and timing of spawning and the probable early life-history characteristics of toothfish, the drift of eggs and larvae over a 6–24 month period were investigated using an oceanic circulation model linked to the high-resolution global environmental model (HiGEM). Model outputs indicated that the locations of toothfish larvae after an 18–24 month period were moderately consistent with the distribution of the smallest toothfish taken in the toothfish fishery.
The hypothesis presented is that D. mawsoni in CCAMLR Subareas 88.1 and 88.2 spawn mainly on the ridges and banks of the Pacific-Antarctic ridge to the north and east of the Ross Sea. The spawning appears to take place during the austral winter and spring. Depending on the exact location of spawning, eggs and larvae become entrained by the Ross Sea gyres, and may 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. As they mature, the fish gradually move deeper out onto the continental slope where they gain condition before undergoing a northwards spawning migration to the Pacific-Antarctic Ridge to start the cycle again. Toothfish probably remain in the northern area for 6–18 months before migrating back to the slope to regain condition.