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

Aggressive behavior of male Sockeye Salmon (Oncorhynchus nerka) competing for the same female, underwater view in an Alaskan stream during autumn.

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

A male Sockeye Salmon (Oncorhynchus nerka) fends off an intruding male with the gape threat in an Alaskan stream during early summer.

Male Sockeye Salmon (Oncorhynchus nerka) threatens another male by raising his formidable jaws with this tilted head posture in an Alaskan stream during early summer.

Male Sockeye Salmon (Oncorhynchus nerka) threatens another male by raising his formidable jaws with this tilted head posture in an Alaskan stream during early summer.

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

Male Sockeye Salmon (Oncorhynchus nerka) threatens another male by raising his formidable jaws with this tilted head posture in an Alaskan stream during early summer.

Pink salmon (Oncorhynchus gorbuscha) probes her redd while her alpha male guards in an Alaska stream during summer.

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

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

A female Sockeye Salmon (Oncorhynchus nerka) uses her anal fin to probe her redd while a jack is positioned downstream. Underwater view in an Alaskan stream during the summer.

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

Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) probes her redd while a male guards 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

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

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

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) 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...

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

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

While her alpha male guards, a female Sockeye Salmon, also known as Red Salmon (Oncorhynchus nerka) excavates her redd in an Alaskan stream near Cordova, South-central Alaska; Alaska, United States of America

A male Pink Salmon (Oncorhynchus gorbuscha) among others of the same species and Dolly Varden Charr (southern form; Salvelinus malma lordi) form a dense school at the bottom of a deep pool during their spawning migration in an Alaskan stream during...

Competing male Sockeye salmon (Oncorhynchus nerka) in an Alaskan stream during summer.