Output of population growth and fishing model for Longspined sea urchins (Centrostephanus rodgersii)

This study created a size-structured stock assessment model to examine the population dynamics and fishing impacts on the long-spined sea urchin (Centrostephanus rodgersii) on the east coast of Tasmania, Australia. The model tracks urchin abundance and growth through size classes over time, using a transition matrix to determine how individuals grow each year, for nine (9) East Coast Tasmanian regions described by Ling and Keane (2018). It begins in 1960 with no population, reflecting the species' first recorded presence in Tasmania in 1978. The model runs until 2160, but the focus of the paper and results is for management options in the next 5 to 10 years, plus retrospective examination for the past 15 years since commercial fishing began. The model generates data through the model testing and fitting process. Output files are defined by three 'classes' (biomean, fitsum, nevermean), with each class producing results for the nine different geographic regions. (1) 'biomean' is predicted urchin density (kg/m2) for each region; (2) 'fitsum' is the Rstan-produced model fit for each region, where the model provides a fit of an equation for recruitment over time based on a sigmoidal increase function; (3) 'nevermean' is the predicted/projected urchin density if no commercial fishing ever occurred for each region. The modelling process is fully described in the associated journal article (in final preparation). A description of files is provided in the 'Lineage' section of this record.