found that 2% of birds nesting in the colony on Bass Rock search for fish at Dogger Bank, between away. It is likely that they fly further than this while foraging, possibly up to double the distance; normally they fly less than . Some studies have found that the duration and direction of flights made while foraging for food are similar for both sexes, although there are significant differences in the search behaviour of males and females. Female northern gannets are not only more selective than males in choosing a search area: they also make longer and deeper dives and spend more time floating on the surface than males. Gannets will follow fishing boats or cetaceans to find discarded or injured fish. They forage from heights of up to with no clear preference, and typically dive between . They dive with their bodies straight and rigid, wings tucked close to the body but angled back, extending beyond the tail, before piercing the water like an arrow. They control the direction of the dive using their wings and tail, and fold their wings against the body just before impact. Birds can hit the water at speeds of up to . This allows them to penetrate up to below the surface, and they will swim down to an average , sometimes deeper than . The bird's subcutaneous air sacs may have a role in controlling their buoyancy. Gannets usually push their prey deeper into the water and capture it as they return to the surface. When a dive is successful, they swallow the fish underwater before surfacing, and never fly with the fish in their bill. Larger fish are swallowed headfirst, smaller fish are swallowed sideways or tail-first. The fish is stored in a branched bag in the throat and does not cause drag when in flight. Their white colour helps other gannets to identify one of their kind and they can deduce the presence of a shoal of fish by this diving behaviour; this in turn facilitates group foraging, which makes capturing their prey easier. The colour also makes the gannet less visible to the fish underneath. Northern gannets also forage for fish while swimming with their head under water. They eat mainly fish in length that shoal near the surface. Virtually any small fish (roughly 80–90% of their diet) or other small pelagic species (largely squid) will be taken opportunistically.