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.

Sockeye Salmon (Oncorhynchus nerka) spawning pair positioned over a redd that is under construction in an Alaskan stream during early 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.

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

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

Pink Salmon (Oncorhynchus gorbuscha) probes her redd in an Alaskan intertidal stream during summer.

Chum Salmon (Oncorhynchus keta) spawning migration in an Alaskan stream during the summer.

Chum Salmon (Oncorhynchus keta) spawning migration in an Alaskan stream during the summer.

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

Ocean bright Coho Salmon (Oncorhynchus kisutch) on their spawning migration. Underwater view in an Alaskan stream during autumn.

Male Pink Salmon (Oncorhynchus gorbuscha) underwater in an Alaskan intertidal stream during the summer.

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) spawning pair in an Alaska stream during the summer, South-central Alaska; Alaska, United States of America

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) male threatening a challenger by also raising his snout 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

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

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

This female Sockeye Salmon (Oncorhynchus nerka) is creating a superimposition by excavating on an existing redd, South-central Alaska; Alaska, United States of America

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