The availability and spatial coverage of fishery-dependent and independent data for stock assessment can be reduced by management-driven catch reductions and expansion of areas closed to fishing. Baited remote underwater stereo-video (stereo-BRUV) is a non-extractive method for sampling fish assemblages that has been widely adopted for cost-effective collection of fish abundance and length data, mainly for conservation and research. To our knowledge, length frequency distribution (LFD) data from stereo-BRUVs have not previously been used directly in stock assessments. We compared fishing mortality estimates derived from a data-limited, length-based catch-curve method applied to LFD data from stereo-BRUVs and from extractive line fishing. For pink snapper Chrysophrys auratus and breaksea cod Epinephelides armatus off south-western Australia, stereo-BRUVs produced mortality estimates comparable to line fishing, as full selection occurs well below maximum length. For several smaller, incidentally caught species, full selection near maximum size prevented reliable estimates. Extractive sampling and ageing remain essential, but stereo-BRUVs offer a complementary, cost-effective source of length data for assessing exploited stocks and broader conservation metrics.