Extreme environmental events that trigger mass mortalities are making fisheries management more challenging. Catastrophic events can have unforeseen impacts on fished resources outside the scope of fishery models and management plans. Mass mortality events (MME) that rapidly reduce densities can decrease the productivity of Haliotis spp. abalone and other benthic free spawning marine invertebrates that require minimum densities for reproductive success. Density-based indicators using fishery-independent measures of density on the fishing grounds serve as an important alternative source of information for management. In northern California, this approach is used to manage the recreational red abalone Haliotis rufescens fishery using densities at key fished sites to guide management. In 2011, a harmful algal bloom (HAB) impacted the southern region of the fishery providing a test of the density-based indicators. Surveys following the HAB revealed a 35% decrease in average density in the southern portion and a decrease in the fishery overall. Empirical fishery-independent density surveys could be used in a range of fisheries for detection of impacts from nonclimate-related stressors such as overfishing and pollution as well as climate-related stressors such as warming, acidification, hypoxia, and disease bolstering climate-ready management. Ecosystem indicators may also be used as early indicators of future changes to productivity. As climate change is predicted to increase the intensity and frequency of MME, managers will need to use sensitive indicators to inform effective climate-ready management responses.