Input data for the 2018 stock assessment of pāua (Haliotis iris) for PAU 5D

This report describes the data inputs to the 2018 stock assessment of New Zealand abalone, pāua (Haliotis iris), in quota management area (QMA) PAU 5D. The PAU 5D QMA covers the eastern coast of Southland and the Otago coast. Data inputs to the stock assessment were catch, catch-per-unit-effort (CPUE), catch sampling length frequency from commercial sampling (CSLF), growth data from tagging, and maturity. There were three years of additional data since the preceding assessment in 2016, e.g., catch data from 2015–16, 2016–17 and 2017–18.

The 2018 stock assessment also included a number of developments and updates to the modelling approach for CPUE, CSLF and growth and maturity data. For CPUE data, two previously separate time series with different resolutions for key covariates were merged by specifying the relationship between the two resolutions within the model structure. The accuracy of the effort variable was also improved by accounting for the probability that diver effort was reported individually or at the level of the crew. For the length-frequency composition data (CSLF), samples were standardised assuming a Dirichlet-Multinomial error distribution instead of rescaling them as in previous stock assessments. For the growth model, a new formulation based on a meta-analysis of growth across all pāua QMAs led to a new, less informative growth prior for population-wide growth in PAU 5D.