The reproductive ecology of Patagonian toothfish (Dissostichus elginoides, Smith 1898) around the sub-Antarctic island of South Georgia : spatial and temporal patterns and processes spanning two decades of data

• Main Author: Brigden, Katie
• Format: Dissertation
• Language: English
• Published: University of Aberdeen 2019
• Subjects: Fishery management; Patagonian toothfish

This thesis aimed to describe trends in the reproductive and recruitment processes of Dissostichus eleginoides at South Georgia, to update and enhance the knowledge and understanding of life history processes, and examine the implications of variability within such processes. A long-term fisheries dataset was utilised to define key reproductive traits and spawning dynamics of D. eleginoides at South Georgia. Multi-year spawning site fidelity was revealed through the identification of spawning hotspots, and the timing of female spawning was shown to have shifted later, leading to a shorter spawning duration. Reduced length and weight of spawning fish was evident across the time period examined and fewer later maturity stage females were observed in conjunction with increased proportions of early stage females. Histological analysis of D. eleginoides ovaries provided the first microscopic descriptions of maturity stages at this location. The use of histological and macroscopic staging with gonadosomatic index data provided a detailed description of the reproductive cycle of female D. eleginoides, affording an enhanced understanding of the maturation process. Such information was further utilised within the examination of D. eleginoides body condition (calculated as relative condition factor, Kn), in order to identify and describe relationships between energy allocation and reproduction. Intra- and inter-annual variability in Kn was demonstrated; and a significant relationship between depth and Kn was revealed, with increased body condition at shallower depths. Sea surface temperature, Southern Oscillation Index, and krill density were not found to significantly influence Kn. The use of an individual based model to examine D. eleginoides egg/larval distribution demonstrated the importance of spawning sites and retention areas in contributing most to retention. Transport pathways between spawning sites and retention areas were identified, revealing the influence of underlying physical processes. These are subject to considerable intra- and inter-annual variability, and act as a significant driver of retention and dispersal of D. eleginoides early stages. Spawning location was found to be important to retention, with oceanographic flows differentially impacting on spawning sites. This new information on key life history processes updates the ecological understanding of D. eleginoides and provides essential knowledge to informing management and policy.