Marine organisms are influenced by environmental variability and fishery and cephalopods are especially plastic in their response to exogenous factors. Underlying mechanisms of interactions are often unclear and complex. The ommastrephid jumbo squid (Dosidicus gigas) is an important component in the ecosystems of the Eastern Pacific Ocean and like other cephalopods rapidly changes abundances of its populations and their size structure. Results of the present work show that the morphological and life history traits of D. gigas respond highly variable to changing environmental conditions. Fishery impacts indirectly and rather positive through the reduction of competitors and predators. A synchronous change in the state of expression of traits occurred after the strong La Nina/El Nino-sequence 1996 to 1998. The elevated energetic requirements of the new states compared to those before the shift lead to the conclusion that the changes in traits follow an energy optimization strategy that allows jumbo squid to adjust to changing availability of prey and emphasize either in survival of the population or the increase of individual fitness
