Indexing maturation of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region

The longline fisheries for Antarctic toothfish (Dissostichus mawsoni) in subareas 88.1 and 88.2 have provided more than a decade of observations to aid in understanding the life history and ecology of toothfish. Updated spawning ogives for males and females support the currently used values. Using histological samples, a summer GSI threshold of 1% appears to be a good indicator of vitellogenic fish developing to spawn in the upcoming season. Evidence is accumulating that almost all Antarctic toothfish in the northern SSRUs have spawned in the previous season and are preparing to spawn in the upcoming season. Observations of post-spawning fish on the slope indicate that some females either spawn on the slope or return to the slope in early spring. The absence of high condition fish in the north indicate that any northward migration occurs in late autumn or winter. Determination of fish movement during the winter period requires winter sample collection from the northern area.