The aim of this research was to gain a better understanding of the ecology and life history of the deepwater notothenid, Dissostichus eleginoides, on the Patagonian Shelf. Archival tagging revealed strong site fidelity of adult toothfish with the majority of fish remaining within 50km of release. Furthermore depth data revealed three behavioural patterns showing feeding, seasonal and spawning activities. The trophic ecology of five notothenioids was studied, examining resource utilisation and niche separation on the Falkland’s shelf. Spatial, ontogenic and seasonal variations in the parasite fauna for juvenile D. eleginoides are described and potential species for use as biological tags to study toothfish population structure are suggested. Validated age readings gave maximum estimated ages of 35 (L = 214.3cm) and 26 years (L = 126.3cm) for females and males respectively and reasons for this sexual dimorphism are discussed. Comparisons of otolith transition zones and growth rates from different regions shows toothfish have adapted their life history traits dependant on their environmental and hydrological surroundings, with populations in warmer areas growing quicker than those in cooler waters. Reproduction in toothfish is discontinuous and group synchronous and final spawning was found to occur in batches. Toothfish predominantly spawn only in one region around the Falklands, on the Burdwood Bank, mainly during July/August. Evidence of skipped spawning was identified indicating that not all fish spawn annually and this aspect is discussed in terms of body condition, periodic strong recruitment and the lack of large scale migrations of adult toothfish. Toothfish around the Falklands have a higher fecundity compared to other regions, a potential adaption to living north of the polar front. This new information on age, growth, reproduction and movements of toothfish, combined with its role in the Patagonian shelf and slope ecosystems, is vital for accurate stock assessment and hence sustainable fisheries management.

Patagonian toothfish (Dissostichus eleginoides) or "Chilean sea bass" support a valuable and controversial fishery, but the life history is little known and longevity estimates range from ~20 to more than 40 or 50 yr. In this study, lead-radium dating provided validated age estimates from juveniles to older adults, supporting the use of otoliths as accurate indicators of age. The oldest age groups were near 30 yr, which provided support for age estimates exceeding 40 or 50 yr from grow zone counts in otolith sections. Hence, scale reading, which rarely exceeds 20 years, has the potential for age underestimation. Lead-radium dating revealed what may be minor differences in age interpretation between two facilities and findings may provide an age-validated opportunity for the CCAMLR Otolith Network to reassess otolith interpretations. Orange roughy (Hoplostethus atlanticus) support a major deep-sea fishery and stock assessments often depend on age analyses, but lifespan estimates range from ~20 to over 100 yr and validation of growth zone counts remained unresolved. An early application of lead-radium dating supported centenarian ages, but the findings were met with disbelief and some studies have attempted to discredit the technique and the long lifespan. In this study, an improved lead-radium dating technique used smaller samples than previously possible and circumvented assumptions that were previously necessary. Lead-radium dating of otolith cores, the first few years of growth, provided ratios that correlated well with the ingrowth curve. This provided robust support for age estimates from otolith thin sections. Use of radiometric ages as independent age estimates indicated the fish in the oldest group were at least 93 yr. Lead-radium dating has validated a centenarian lifespan for orange roughy. To date, radium-226 has been measured in otoliths of 39 fish species ranging from the northern Pacific and Atlantic Oceans to the Southern Ocean. In total, 367 reliable radium-226 measurements were made in 36 studies since the first lead-radium dating study on fish in 1982. The activity of radium-226 measurements ranged over 3 orders of magnitude (<0.001 to >1.0 dpm.g⁻¹). An analysis revealed ontogenetic differences in radium-226 uptake that may be attributed to changes in habitat or diet. Radiometric age from otolith core studies was used to describe a radium-226 uptake time-series for some species, which revealed interesting patterns over long periods. This synopsis provides information on the uptake of radium-226 to otoliths from an environmental perspective, which can be used as a basis for future studies.