Chum Salmon (Oncorhynchus keta) spawning; Underwater view in an Alaskan stream during 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.

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.

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.

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

Female Sockeye Salmon (Oncorhynchus nerka) attempting to oust a sneaker male by using the gape threat 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.

Female Sockeye Salmon (Oncorhynchus nerka) raising a cloud of sediment while digging her redd 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.

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

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

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) 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

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,...

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 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

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 ready to spawn Sockeye Salmon (Oncorhynchus nerka) male in an Alaskan stream at the start of summer.