This data package consists of two files to accompany the manuscript Smith J., Flukes E., Keane J.P. (2024) The risky nightlife of undersized sea urchins. Marine and Freshwater Research IN PRESS. Dataset A: 211 Centrostephanus rodgersii (longspined sea urchin) were measured for test diameter and spine canopy at Fortescue Bay, Tasmania, Australia in May-June 2023 (FB_TD_SC.csv) Dataset B: Urchin movement data from Flukes et al. 2023 and associated urchin sizes measured in this study (whole_measured_df.csv)

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.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the Nubeena region, and its 3 subsites: Cape Raoul, Salters Point and Wedge.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the Four-mile Creek region, and its 3 subsites: Falmouth, Ironhouse Point and Saltwater Inlet.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the North Bruny Island region, and its 3 subsites: Patrick's Bight, Trumpeter Point and Yellow Bluff.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the Wineglass Bay region, and its 3 subsites: Boot, Nuggets and Wineglass.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the South Bruny Island region, and its 3 subsites: Mangana Bluff, Bay of Islands and Cape Conella.

Timed GPS-tracked swims using SCUBA (45 and 30 minutes), were used to assess the changes in frequency and size of Centrostephanus rodgerii incipient barrens in eastern Tasmania. The number of C. rodgerii and Heliocidaris erythrogramma in each incipient barren were also assessed.

The spatial extent of C. rodgersii "barrens" was estimated by surveying rocky reef habitat with a towed underwater video system. Sampling took place at 13 regions along the east coast of Tasmania, each comprising 3 subsites, this dataset refers to the Recherche region, and its 3 subsites: Eliza Point, Fisher Point and Actaeons.