According to the studies by trites and donnelly, the most likely reason for the decline in the population of steller sea lions in the gulf of alaska is

I think the correct answer to this is ‘reduced prey quality’.

This is because in the study made by Trites and Donnelly, they found out that steller sea lions were experiencing nutritional stress. Nutritional stress means that although the prey contains all the necessary nutrients, the quantity of prey is not enough due to a reduction in overall biomass of prey locally.