Since its introduction in the Western Atlantic more than 30 years ago, the lionsh (Pterois volitans/miles complex) has spread throughout the Gulf of Mexico and the Caribbean having massive and unprecedented ecological impacts. This invasion is among the most studied marine sh invasions but very little is still really known about the population dynamics of the species and the factors ultimately governing its abundance. We here document a large population crash for the lionsh following its rapid increase in abundance on the Saba Bank following its appearance in 2010. In doing so we document the third case of apparent local population boom-bust event for the Greater Caribbean, and the rst for the Eastern Caribbean. We also document gradual increases in the mean size of lionsh of the Saba Bank that coincided with the increase and subsequent decline in lionsh abundance. Contrary to the previously documented epizootic disease outbreak associated with the population crash observed in the Gulf of Mexico we were unable to nd any signs of the occurrence of epizootic disease. We suggest that the population crash on the Saba Bank might have been due to non-local causes, such as reduced reproductive output in distant larval source populations. Boom-bust dynamics are often witnessed in biological invasions and have critical implications for both understanding and managing invasive species. While the underlying cause for the boom-bust event we document remains unknown, our work helps improve our understanding of this most serious biological invasion.