Studies have shown that the main prey of sperm whales in most areas of the world are cephalopods . But in some areas of the world (New Zealand, North Atlantic and North Pacific), fishes are a substantial part of their diets . The fish eaten by sperms are medium to large (0.3 to 3 m long) . Fishes are a bigger part of male’s diet than female’s, since males are more likely in shallow waters and foraging the bottom .
While foraging, sperms can ingest various animals and inanimate objects. Crabs, mysids, salps, krill, lobsters, tunicates starfishes, jellyfishes, sponges, sea cucumbers, seals, sea birds, wood, coconuts, stones, sand, tin plate, plastic and fishing gear were already found in sperm whale’s stomachs . Some of these items may be ingested intentionally, as “secondary prey items” while foraging, but others may be ingested accidentally while ingesting more typical prey . Plastic bags and fishing gear were probably mistaken for a digestible prey . The ingestion of plastic can lead the animal to death, as seen in this post of “The Animals Post”, where a sperm whale was found with 20 kg of plastic inside her stomach. Fishing gear can also lead the animal to death by its ingestion or entangling, as shown in this rescue video of Italian Coast Guard. Fortunately, the group was set free of the net, but if the Coast Guard didn’t release the animals, they wouldn’t survive.
The main item of sperm whale’s diet is squid. They vary in size from 100g (chiroteuthids) to 400kg (architeuthids, or giant squids) . Figures 1 and 2 show the comparison of squid and sperm whale’s body sizes.
The majority of squids ingested by sperm whales are small, compared with the whale’s body and not particularly nutritious , therefore, sperm whales need to ingest a lot of them. Scientists believe that females ingest 750 squids a day, while males consume 350 of them, but in bigger sizes . Scientists also believe that a bigger squid is more challenging to capture than the small cephalopods . While chiroteuthids (<100 g) are visible and have limited escape responses, an adult of the ommastrephid Dosidicus gigas (Humboldt squid) is large, agile and invisible in the dark deep ocean and quite challenging  demanding more energy to catch.
Summarising: sperm whales can be considered a “nibbler” rather than a “meal eater”, since they have forage continuously in search for food .