Radiometric Age Validation of the Patagonian and Antarctic Toothfishes

The Patagonian toothfish (Dissostichus eleginoides) is one of the dominant fishes in the Antarctic belonging to the family Nototheniidae, the Antarctic cods. Age estimates from otolith growth zone counts indicate the Patagonian toothfish may live to at least 50 years; however, attempts to validate these estimates have been met with limited success. Regular interpretations of age using otoliths in the international community have been used to determine life history characteristics, but observed differences in derived growth parameters have raised the question of whether the differences are real or an artifact of methodological differences. To address the problem age estimates must be validated, but typical validation techniques have limited applicability to deep-water and long-lived fishes. One technique that has been successful is lead-radium dating, which uses the disequilibria of lead-210 and radium-226 in otoliths as a natural chronometer. In this study, otolith age estimation methods used at the Center for Quantitative Fisheries Science (CQFE) in the USA and the Central Ageing Facility (CAF) in Australia have been evaluated using lead-radium dating. The findings provide insight on between facility similarities and differences for the respective ageing methodologies. Both facilities appear to have an ageing bias of just a few years depending on what ages are considered. In general, the trend for both facilities supports agreement on age interpretation with only minor differences. For the oldest age groups (about 26 to 30 years) age estimation was accurate and the findings provide support for age estimates approaching 50 yr using the same age estimate methodology. Antarctic toothfish (Dissostichus mawsoni) are subject to an increasingly important commercial fishery in the Southern Ocean, yet many of their life history characteristics, including vital rates, remain unknown. In this study, Antarctic toothfish were aged using otolith age estimation criteria established for Patagonian toothfish, D. eleginoides, a closely related species. To validate estimated ages, the radioactive disequilibrium of lead-210 and radium-226 in otolith cores was measured and used as an independent chronometer to determine age. Estimated and radiometric ages were in close agreement, confirming age estimation criteria and an annual periodicity of otolith growth zones. Estimated ages indicated longevity of 39 years and von Bertalanffy growth function parameters indicate Antarctic toothfish are relatively slow-growing (k = 0.111), especially in relation to their size (L = 158.9 cm). These vital rates are discussed in the context of the growing Antarctic toothfish fishery.