The following diagram shows an oceanic food web. At what trophic level do the killer whales primarily feed?

The killer whales primarily feed on the secondary consumers in the oceanic food web.

Explanation:

Killer whales are the tertiary consumers and occupy the highest position in the ocean food web. They are predating carnivores and feed on secondary consumers like other fishes, marine animals like leopard seals, sea turtles, dolphins, sea birds, etc. These secondary consumers in turn feed on primary consumers like zooplanktons, small fishes etc which feed on the primary producers like phytoplanktons. The energy flow is highest at the primary producer level and decreases as it goes up to the consumer levels.