Length- and age-at-spawning of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea
This study uses histological assessments to determine age- and length-at-spawning for female and male Antarctic toothfish (Dissostichus mawsoni) from fish sampled in the Ross Sea spanning the 2000–2009 fishing seasons. A characterisation of the oocyte developmental cycle of D. mawsoni shows that once development begins, oocytes grow and accumulate at the cortical alveoli stage for at least one year. Individual oocytes are then recruited into the vitellogenic phase over at least a 6–12 month period, resulting in a developed group of oocytes accumulating at the final maturation stage by approximately May each year. The age at 50% spawning for females on the Ross Sea slope region is 16.6 years (95% CI 16.0–17.3) or 133.2 cm (95% CI 130.9–135.7) by length. On average,
males spawn at a younger age with an A50% of 12.8 years (95% CI 11.9–14.0) or 120.4 cm (95% CI 114.8–126.7) by length. Evidence of skip-spawning was observed for females only and results in a flatter, right-shifted ogive, increasing the functional difference between male and female ogives. The degree to which the overall population ogive is biased right (older) by applying the slope-derived ogive to the northern Ross Sea region depends on the proportion of the total population occurring in the northern Ross Sea region, which is currently unknown.