The redd may sometimes contain 5,000 eggs covering . The eggs usually range from orange to red. One or more males approach the female in her redd, depositing sperm, or milt, over the roe. The female then covers the eggs by disturbing the gravel at the upstream edge of the depression before moving on to make another redd. The female may make as many as seven redds before her supply of eggs is exhausted. Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in ring formation around an earbone called the otolith (annuli), analogous to the growth rings visible in a tree trunk. Freshwater growth shows as densely crowded rings, sea growth as widely spaced rings; spawning is marked by significant erosion as body mass is converted into eggs and milt. Freshwater streams and estuaries provide important habitat for many salmon species. They feed on terrestrial and aquatic insects, amphipods, and other crustaceans while young, and primarily on other fish when older. Eggs are laid in deeper water with larger gravel and need cool water and good water flow (to supply oxygen) to the developing embryos. Mortality of salmon in the early life stages is usually high due to natural predation and human-induced changes in habitat, such as siltation, high water temperatures, low oxygen concentration, loss of stream cover, and reductions in river flow. Estuaries and their associated wetlands provide vital nursery areas for the salmon prior to their departure to the open ocean. Wetlands not only help buffer the estuary from silt and pollutants, but also provide important feeding and hiding areas. Salmon not killed by other means show greatly accelerated deterioration (phenoptosis, or "programmed aging") at the end of their lives. Their bodies rapidly deteriorate right after they spawn as a result of the release of massive amounts of corticosteroids. Diet As adults, salmon eat a variety of other sea creatures, including smaller fish such as lanternfish, herrings, sand lances, and barracudina. They also eat krill, squid, and polychaete worms. They are also known to eat grasshoppers. Ecology Bears In the Pacific Northwest and Alaska, salmon are keystone species, supporting wildlife such as birds, bears and otters. The bodies of salmon represent a transfer of nutrients from the ocean, rich in nitrogen, sulfur, carbon and phosphorus, to the forest ecosystem. Grizzly bears function as