Little is known of the relationship between instantaneous natural mortality rate, M (year−1), and body weight, W (g), for the lake-resident life stages of sockeye salmon Oncorhynchus nerka and kokanee (lacustrine sockeye salmon), despite the importance of the M–W relationship for modeling fishery management options. This study provided estimates of the two parameters of the allometric relationship M = 1.38W−0.19based on nonlinear regression of sockeye salmon egg–fry and egg–smolt survivals on fry and smolt weights reported in the literature. The values of both parameters were low compared with values reported from data sets that included marine iteroparous fish species and larval fish but were similar to values calculated from production–biomass ratios of lake fish populations. The difference suggests that nonpredation mortality plays a minor role in the population dynamics of juvenile sockeye salmon due to their relatively large size at emergence. The M–W relationship provided reasonable predictions of M for juvenile kokanee, based on M calculated from literature reports of kokanee density at age. Predictions of M also appeared reasonable when extrapolated to adult kokanee body weights, based on a comparison with M predicted by four previously published models of adult fish M. The M–W relationship has three potential applications to fishery management: (i) modeling of O. nerka population dynamics; (ii) back-calculating density of age-0 kokanee from density of age-2 kokanee; and (iii) estimating fishing mortality rate of exploited age-classes of kokanee by subtracting predicted M from total mortality rate.