ABSTRACT The population dynamics of jumbo squid Dosidicus gigas from northwest Mexico was evaluated for the period 1974-2012 using Schaefer's model, where model parameters were estimated with the catch maximum sustainable yield method (Catch-MSY) using two prior intrinsic population increase rate (r) range values (1.0 to 2.0 and 1.5 to 2.0). Estimated parameters with both prior r ranges were 1.23 and 1.68 yr−1 for r and 243,836 and 190,468 ton for carrying capacity (k), respectively. Corresponding management quantities were 75,147 and 80,098 ton for the maximum sustainable yield (MSY) and 121,918 and 95,234 ton for the biomass at MSY (BMSY). Estimated jumbo squid biomass dropped below the BMSY after 2003, and near to 0.2 k in 2012. The Schaefer's model showed that declines in estimated biomass were preceded by catches that exceeded the MSY. Strong El Niño-Southern Oscillation events can change the availability of jumbo squid in northwest Mexico through migratory processes and phenotype changes in maturation size, but stock biomass variability is most likely to be caused by fishing.