An Eulerian approach was applied through a daily data set (n = 51) on mantle length frequencies of jumbo squid Dosidicus gigas derived from a small jigging fleet (5 vessels), which stayed fishing in the same area off Mulegé, central Gulf of California. Data were corrected for observation bias introduced by the fishing gear (jigs) and were used to analyze population structure and growth-related parameters by modal progression analysis. Sexual maturity stages and size structure showed a predominance of medium-size immature specimens, both male and female. Mean size of jumbo squid showed a progressive increment throughout the fishing period that could be associated with growth or migration. Our estimations of growth rates were higher (3.15–3.85 mm/day) than those calculated previously for D. gigas with other methods in the same region (Gulf of California). This apparent overestimation of growth rates could be associated with a bias introduced by migration. In fact, our study area is part of some migratory routes known for this species and could be considered a transitory feeding ground for medium-size jumbo squid. The most possible explanation for the progressive increment of size (mantle length) during the fishing period considers a dynamic interaction between growth and migration.