Abstract

The role of marine mammals in ecosystems has been evaluated mainly in species of high trophic level and results indicate that they influence the structure and functioning of biological communities. In this study the trophic role of the humpback whale was analyzed using an ecosystem model of the Francisco Coloane Coastal Marine Protected Area, Magellan Strait. The model was built with the Ecopath with Ecosim software that also allowed quantification of trophic interactions, predation mortality and prey consumption by the whales. Indices of network analysis were calculated and the removal of whales from this ecosystem was simulated. The humpback whale presented an intermediate trophic level of 3.4 and represented the most important predator for lobster krill and euphausiids, explaining 51% and 36% of total mortality in those groups, and the second predator in importance for the Fuegian sprat, after the long-tailed hake. Network analysis indicated that food web organization and development was determined by low trophic levels (i.e. phytoplankton and mesozooplankton), while fish played a major role in the transfer of energy. The removal of humpback whale biomass in the model produced a change in food web structure. This study approaches the trophic role of whales in Chilean waters for the first time, indicating that humpback whales in the Magellan Strait play a role in the maintenance of the ecosystem organization.