Weddell seals prey upon fish, squid and octopus, prawns and crabs, although their diet may vary slightly based on seasonal changes, according to TravelWild. Their favorite fish species to prey on are emerald rock-cod and Antarctic silverfish. Weddell seals seem to eat their food underwater.
Because of the wide variety of food that they eat Weddell seals are generally carnivores, but are also more specifically pesectivores and molluscivores. They feed on both pelagic, or mid-water, and bottom dwelling or benthic fish.
Weddell seals can hold their breath for 45 minutes; they regularly dive 600 meters in search of food and have been reported to have gone as deep as 720 meters. They are incredibly stealthy hunters and are aided by their ability to swim at high speeds and keen eyesight. In addition they have sensitive whiskers or vibrissae which help to detect prey in the darkness of a long Antarctic winter. Weddell seals have been documented blowing bubbles into crevices in the ice to scare the fish out so that the seals can eat them.
In the summer, Weddell seals prefer to hunt at night rather than during the day. It's theorized that they use tidal cues to determine when it is best to hunt.