Underwater view of a competing sockeye salmon (Oncorhynchus nerka) in Power Creek near Cordova, Alaska in the summer; Alaska, United States of America

Underwater view of migrating pink salmon (Oncorhynchus gorbuscha) in Eccles Creek near Cordova, Alaska in the summer; Alaska, United States of America

Underwater view of a female sockeye salmon (Oncorhynchus nerka) in Power Creek near Cordova, Alaska in the summer; Alaska, United States of America

Underwater view of developing sockeye salmon (Oncorhynchus nerka) eggs in Power Creek near Cordova and Prince William Sound; Alaska, United States of America

Underwater view of a male pink salmon (Oncorhynchus gorbuscha) in Hartney Creek near Cordova, Alaska in the summer; Alaska, United States of America

Male Sockeye Salmon (Oncorhynchus nerka) threatens another male by raising his formidable jaws with this tilted head posture, underwater view in an Alaskan stream during early summer; Cordova, Alaska, United States of America

Sockeye Salmon (Oncorhynchus nerka) spawning pair positioned over a redd that is under construction, Alaska

A Sockeye Salmon (Oncorhynchus nerka) spawning pair Underwater view in an Alaskan stream during the summer.

Chum Salmon (Oncorhynchus keta) spawning pair underwater view in an Alaskan stream during summer.

A Sockeye Salmon (Oncorhynchus nerka) spawning pair in an underwater view in an Alaskan stream during the summer.

Sockeye Salmon (Oncorhynchus nerka) in the act of spawning in an Alaska stream during summer.

Underwater view of maturing coho salmon (Oncorhynchus kisutch) holding in a pool in Hartney Creek near Cordova, Alaska in autumn; Cordova, Alaska, United States of America

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) spawning pair in an Alaskan stream during the summer; Alaska, United States of America

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) spawning pair in an Alaskan stream during the summer; Alaska, United States of America

A Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) pair in the act of spawning in an Alaskan stream during the summer; Alaska, United States of America

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) male threatening a challenger by also raising his snout in an Alaskan stream during the summer; Alaska, United States of America

Mature Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) male in nuptial (breeding) coloration in an Alaskan stream during the summer; Alaska, United States of America

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) male crosses over a female as part of courtship in an Alaskan stream during the summer; Alaska, United States of America

Male Chinook Salmon, also known as King Salmon (Oncorhynchus tshawytscha) prior to spawning in a tributary of the Deshka River in summer; Alaska, United States of America

Incidental tree branch bites can result from the aggressive behavior of male Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) competing to spawn in an Alaskan stream during the summer; Alaska, United States of America

Anticipating spawning, male Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) approach a female probing her redd in an Alaskan stream during the summer; Alaska, United States of America

A female Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) attacking a female who is excavating a redd that is too close to hers in an Alaskan stream during the summer; Alaska, United States of America

Female Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka), covers her redd immediately after spawning as the male guards in an Alaskan stream during the summer. Sperm that has not drifted downstream clouds the water above the redd; Alaska,...

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) spawning in an Alaskan stream during the summer. Two competing males are lurking nearby, one is visible at the right edge of the frame and the other, a jack or precocial male, is visible...

Underwater view of a sockeye salmon (Oncorhynchus nerka) spawning pair and a challenger male in Eccles Creek near Cordova, Alaska in the summer; Alaska, United States of America