In Queen Charlotte Sound, three broad troughs over 350 m in depth slice inland across this shelf and are separated by wide shallow banks. Pacific cod, sole, lingcod and sablefish are found throughout the continental shelf but are concentrated around the shallow banks. Salmon rivers dissect the mainland coast. Clams, shrimp and prawn are relatively abundant. Over a million seabirds breed in the region, including the largest concentrations of rhinoceros auklets, and Leach's and fork-tailed storm-petrels in British Columbia. Queen Charlotte Sound is also a vital feeding area for millions of breeding, summering and migrating seabirds and waterfowl. Grey whales, harbour and Dall's porpoises, Pacific white-sided dolphins and northern fur seals are common visitors, while harbour seals and Stellar sea lions make the region home. About 190 resident killer whales in 16 pods (close-knit family groups) cruise the southern waters of the region. A small population of sea otters has recently established itself along the coast, a positive sign for the recovery of this endangered species. This region is not yet represented in the national marine conservation areas system. Four representative marine areas have been identified: Blackfish Sound, Queen Charlotte Strait, Goose Island Bank and Laredo Sound.