Standardized catch-per-unit-effort (CPUE) from commercial fishing underpins most stock assessments in the Southern and Eastern Scalefish and Shark Fishery (SESSF). However, increased fishing power, climate-driven shifts in fish distribution and productivity, and the need to monitor stocks under rebuilding strategies are collectively eroding confidence in CPUE as a reliable abundance index. Close-kin mark-recapture (CKMR) — which estimates mature abundance from parent–offspring and half-sibling pairs offers a robust, fishery-independent alternative. CKMR accumulates information over time (reducing future sampling needs), and is robust to the distributional changes affecting CPUE.
We present CKMR assessment designs for 19 stocks identified as priorities for the SESSF, spanning commercially important target species and ecologically significant food-web components. For each stock, we estimated annual sample sizes required over a five-year period to achieve coefficients of variation (CV) of 20% and 25% on spawning biomass. Two sampling strategies were compared: a 'flat' design (equal sampling across age classes, more efficient but harder to implement) and a 'catch' design (sampling proportional to catch age distribution, straightforward but less efficient). These bracket the range of realistic programs.
Required sample sizes span several orders of magnitude, broadly tracking population abundance. Very abundant small-bodied species (e.g. Jack Mackerel, Redbait, School Whiting) require large samples, while large-bodied or depleted stocks (e.g. Pink Ling East, Blue-eye Trevalla, Gummy Shark) have more achievable requirements. Orange Roughy East and Bight Redfish emerge as poor CKMR candidates due to fishing selectivity-maturity overlap and excessive estimation lags.
For two hypothetical examples, ongoing sample collection resulted in the precision advantage of flat over catch sampling disappearing within three additional years and required annual sample sizes fell to roughly 50% of initial levels by 2040. CKMR offers cost-effective, climate-resilient stock assessment for some species, and a possible monitoring tool for those under rebuilding strategies.