Toothfish life history
There are two main species of toothfish in the Southern Ocean: the Patagonian and Antarctic toothfish.
The Patagonian toothfish (Dissostichus eleginoides) lives in predominantly subantarctic waters. The Antarctic toothfish (Dissostichus mawsoni) lives predominantly in Antarctic waters, and is continuously distributed around the Antarctic continent. [NIWA]
Antarctic toothfish size distribution in the Ross Sea
Juvenile toothfish (40–80 cm in length) are mainly found on the southern Ross Sea shelf and around the Balleny Islands, at depths of 750 m or less. Sub-adult and maturing (80–130 cm) toothfish have been found at more than 750 m in deeper parts of the shelf and along the continental slope. The largest toothfish (>130 cm) are typically found in deeper parts of the slope and on banks, ridges and seamounts in the north. Sex ratios at birth are approximately 50:50. Catches of adults on the slope are approximately 60% female, while catches in the north are approximately 70% male.
Results from a tagging programme suggest that toothfish of all sizes are quite sedentary, with the majority being recaptured within 50 km of release. Fish found further than 50 km from where they were released were generally sub-adult and maturing fish moving between the deeper parts of the Ross Sea shelf and slope. Mature adults released on the shelf and slope have been recaptured on the northern grounds and vice versa. [NIWA]
Reproduction and life cycle
It is likely that spawning occurs between June and September on the Pacific-Antarctic ridge to the north of the Ross Sea. Although Antarctic toothfish eggs or postlarvae have not yet been caught, eggs and larvae spawned in the northern region would be transported by the Ross Sea gyre and carried passively east and then south to the Antarctic coastline.