Abstract Cardinal snapper Pristipomoides mac- rophthalmus is a commercially important, but com- monly misidentifed, deepwater species in artisanal and semi-industrial fsheries throughout the Carib- bean Sea. As with many tropical deepwater fshes, lit- tle is known about the biology or ecology of the spe- cies. Bomb radiocarbon (14C) dating was applied to cardinal snapper sagittal otoliths collected from the waters of Belize and Honduras during 2015–2019 to investigate the lifespan of the species from thin-sec- tioned otoliths with an evaluation of otolith mass as a proxy for age. Ages estimated from 28 thin-sectioned otoliths ranged from 7 to 68 years for fsh that covered the range lengths and otolith masses available. Radio- carbon values were measured for each cardinal snap- per otolith core, and two fsh (one each from Belize and Honduras) had 14C signatures consistent with pre-bomb values, efectively validating a lifespan of at least 60 years. A curvilinear relationship between otolith mass and estimated age was robust (r 2=0.95) and is likely to produce age estimates with similar margins of error to traditional, more labor-intensive methods, such as counting increments from thin-sec- tioned otoliths. The otolith mass-to-age relationship is a well-supported method that provides a simple, low- cost approach that can be used by fshers, managers, and other stakeholders to assess the age composition of the cardinal snapper stock in the western Carib- bean Sea for present and long-term monitoring.