| In Alaska, the crossing-over to other streams allows salmon to populate new streams, such as those that emerge as a glacier retreats. The precise method salmon use to navigate has not been entirely established, though their keen sense of smell is involved. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. However, even in those species of salmon that may survive to spawn more than once (iteroparity), post-spawning mortality is quite high (perhaps as high as 40 to 50%.)
In order to lay her roe, the female salmon uses her tail (caudal fin), to create a low pressure zone, lifting gravel to be swept downstream, excavating a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering 30 square feet (2.8 m2). The eggs usually range from orange to red in color. One or more males will approach the female in her redd, depositing his 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 will make as many as 7 redds before her supply of eggs is exhausted. The salmon will then die within a few days of spawning. |
