Relationship between yellowfin tuna (Thunnus albacares) distribution caught by Iranian purse seiners and environmental variables in the Indian Ocean

Yellowfin tuna (Thunnus albacares) is one of the most important apex predator species that currently catch by Iranian purse seiners in the Indian Ocean and Oman Sea. This study considered the possible relationship of spatial, temporal and some satellite derived environmental variables on yellowfin tuna distribution to finally help implementing of ecosystem based fisheries management for stock recovery program and management of yellowfin tuna. Results of generalized additive model (GAM) (by assuming two distribution; binomial and Gaussian) revealed spatial and temporal explanatory variables plus sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD) and net primary production (NPP) have the greatest impact on yellowfin tuna distribution in both cold and warm season. In addition, the results revealed that latitude had stronger effect on deviance explanation of model in warm season. On the other hand, in cold season, the effect of longitude and environmental variables was clear. In warm season, binomial distribution was explained higher deviance of model, though in cold season deviance explanation of best model was lower than warm season but no significant difference has detected. Since the early step in ecosystem management is the sufficient knowledge on ecosystem and distribution of target species in relationship to environmental variables, therefore this research could help Iranian purse seiners to improve the catch efficiency in order to help to implementing of ecosystem based management in the Indian Ocean.