A preliminary investigation of the possible effects of rhizocephalan parasitism on the management of the crab fishery around South Georgia
Relatively high levels of infection by a rhizocephalan barnacle have been found in the population of the crab Paralomis spinosissima, which has been harvested by a new fishery around South Georgia (Subarea 48.3) since 1992. One of the main effects of the parasite is to render infected animals sterile. Parasitism can therefore reduce the effective spawning stock biomass, and this clearly has implications for stock management.
The possible implications of parasitism for management are investigated by considering a population model that captures the main characteristics of the system. An age-based host-parasite model is constructed, incorporating two scenarios for the stock-recruit relationship of the host: (i) resilience; and (ii) sensitivity to declines in spawning stock. The effects of harvesting both healthy and infected animals are contrasted with the effects of harvesting healthy animals only. Equilibrium and transition dynamics of the models are explored for ranges of parameter values.
Results indicate a need to harvest or remove infected animals from the population. The need is stronger when the population is sensitive to declines in spawning stock. Results highlight the importance of incorporating parasitism in the design of a management strategy for this crab population. The main data requirements for improving on this preliminary study are identified.