We used folk biological classification as a framework for understanding stakeholder perceptions of marine species diversity and its potential consequences for conservation in Puget Sound, Washington. Respondents (N= 99) classified 46 marine species into folk taxonomies, which diverged substantially from a scientific taxonomy. Variation in folk taxonomy structure was related to respondents’ expertise, suggesting that the ways in which people sampled or observed the marine environment led to different perceptions of species diversity within it. Differences in the degree of aggregation among taxa supported the notion that culturally important species are more identifiable. We focused on rockfishes (Sebastes spp.), long-lived species of conservation concern, to demonstrate how different views of biodiversity could lead to divergent perceptions of risk to rockfish populations. Understanding the connection between people's values, goals, and experience and their underlying views of species diversity may help to reconcile differences between stakeholder and scientific perspectives.