Quantitative assessment and management of small-scale fisheries is a persistent problem for fisheries. Crustaceans are particularly challenging for conventional techniques because their lack of permanent hard body parts makes ageing difficult. While a growing body of literature is aimed at developing alternative approaches to small-scale fisheries assessment there are concerns about the indiscriminate application of generic methodologies and the need to address the specific circumstances of fisheries. The length-based assessment of spawning potential ratio (LBSPR) is appealing because it has simple data requirements, a well-developed theoretical foundation, and estimates Spawning Potential Ratio (SPR) an internationally recognized indicator of stock status. With the aim of establishing basic standards and providing structured discussion of the issues raised by its application, this study documents its application to the regionally important blue swimming crab (BSC) (Portunus spp.) fisheries, in Sri Lanka and Indonesia. Our study demonstrates the methods technical feasibility and cost-effectiveness for small-scale BSC fisheries and by extension other small-scale fisheries. In Sri Lanka and Indonesia, these LBSPR assessments are successfully informing discussions about sustainability; focusing discussion on managing size selectivity, one of the few management controls available to fisheries managers in many small-scale fisheries. In Indonesia BSC are first caught at around the size of maturity by trawling and with baited traps without escape gaps, reducing SPR to unsustainable levels. Despite similarly high fishing pressure, in Sri Lanka the larger size of first capture with bottom set nets preserves a sustainable level of SPR. Supported by these assessments, in 2018, that fishery attained a provisional sustainability rating from Seafood Watch. We suggest how LBSPR assessment might be used to adaptively manage size selectivity within the harvest strategy being developed in Indonesia. It is hoped this documentation of the methodology will assist other small-scale fisheries to use this technique similarly.

小型渔业的定量评估和管理一直是渔业的难题。甲壳类动物对常规技术特别具有挑战性，因为它们缺乏永久的硬质身体部位，使老化变得困难。尽管越来越多的文献旨在开发用于小型渔业评估的替代方法，但人们仍对通用方法的不加区别地应用以及解决渔业具体情况的需求感到担忧。基于长度的产卵潜力比（LBSPR）评估很吸引人，因为它具有简单的数据要求，完善的理论基础，并估计了产卵潜力比（SPR）是国际公认的种群状况指标。Portunus spp。）渔业，在斯里兰卡和印度尼西亚。我们的研究表明了该方法在小型BSC渔业以及扩展到其他小型渔业中的技术可行性和成本效益。在斯里兰卡和印度尼西亚，这些LBSPR评估成功地推动了有关可持续性的讨论；将讨论的重点放在管理规模选择性上，这是许多小型渔业中渔业管理人员可用的少数管理控制措施之一。在印度尼西亚，BSC首先通过拖网捕捞，并带有诱饵陷阱，没有逃生间隙，从而将SPR降低到不可持续的水平。尽管面临同样高的捕捞压力，但在斯里兰卡，较大的第一次捕捞和底部设置的渔网可保持可持续的SPR水平。在这些评估的支持下，2018年，该渔业获得了Seafood Watch的临时可持续性评级。我们建议在印度尼西亚正在制定的收获策略中，如何使用LBSPR评估来适应性地管理大小选择性。希望该方法学的文档能够帮助其他小型渔业类似地使用该技术。