Silver warehou are found all around New Zealand and are relatively common around the South Island and on Chatham Rise at depths of 200–800 m. There has never been an accepted stock assessment for New Zealand silver warehou. We applied length-based spawning potential ratio (LB-SPR) analysis to the SWA 3 and 4 stock. LB-SPR uses length frequency data and biological parameters to estimate spawning potential ratio, a measure of the impact of fishing on the potential productivity of the stock. Length frequency data were collated from observer samples and resource surveys, but length frequencies from the resource surveys were too sparse and variable to be used. Observer length frequencies were acceptable, but SPR estimates were not considered plausible, primarily because the assumption of constant recruitment was likely to be violated. The method assumes that a relative reduction in large fish within the proportions at length is caused by mortality, but this could also occur if there had been recent strong recruitment, which was suspected for silver warehou. The hypothesis of recent strong recruitment should be tested through further fish ageing and age frequency analysis.
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