We propose to test three hypotheses to describe the reproductive ecology of Antarctic toothfish (Dissostichus mawsoni):
1) Antarctic toothfish eggs are buoyant and accumulate under sea ice. If true, this would retain eggs near the spawning locations under the vast sea ice extent and once broken up in the spring, may provide access to a productive pagophilic ecosystem for feeding as well as a transport mechanism for subsequent advection patterns, all of which could be impacted by climate change. This would have implications on the understanding where recruiting fish originate and how those patterns may be influenced by changes in sea ice or circulation patterns that affect observed recruitment patterns.
2) Antarctic toothfish spawn throughout the Pacific Antarctic fracture zone. Evidence to date only exists from the west of the region (SSRU 88.1B), yet adult Antarctic toothfish are found much further east and north of the CCAMLR Convention area, which is bounded by latitude 60°S. Obtaining a better understanding of the location and movement of adult spawning toothfish has direct implications on the understanding of those parts of the adult stock that contribute to recruitment, and hence the productivity of the stock assumed in the stock assessment.
3) Biological characteristics of the northern spawning population change as younger, fatter, female fish move to the north for spawning during winter. Evidence to date found no change in these characteristics in June, suggesting sampling later in the spawning season is needed.
We propose to conduct a scientific survey during the austral winter in the northern Ross Sea region to test these hypotheses. The longline and plankton survey is designed to cover key gaps in the knowledge of the life cycle of Antarctic toothfish in the Ross Sea by collecting biological samples from a range of locations in the northern regions of Subarea 88.1 and 88.2 and begin in September 2019. The survey will be coordinated with a corresponding survey targeting Antarctic toothfish spawning dynamics in the southern area of the South Pacific Regional Fisheries Management Organisation (SPRFMO) area at a similar time.