Sockeye Salmon (Oncorhynchus nerka) spawning pair in an Alaskan stream during late summer.

Alpha Sockeye Salmon (Oncorhynchus nerka) male chasing away a rival in an Alaskan stream during early summer.

A female Sockeye Salmon (Oncohynchus nerka) nudges a male away from her redd so that she can work on it, underwater view in an Alaskan stream during summer.

A Sockeye Salmon (Oncorhynchus nerka) male challenges another by gaping in an Alaskan stream during early summer.

A female Sockeye Salmon (Oncohynchus nerka) nudges a male away from her redd so that she can work on it, underwater view in an Alaskan stream during summer.

A Sockeye Salmon (Oncorhynchus nerka) male attempts to nudge away a competitor for the same female in an Alaskan stream during early summer.

Female Sockeye Salmon (Oncorhynchus nerka) uses her anal fin to probe her redd in an Alaskan stream during summer.

Mature male Chum Salmon (Oncorhynchus keta) in an Alaskan stream during the summer.

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

Female Sockeye Salmon (Oncorhynchus nerka) raising a cloud of sediment while digging her redd in an Alaskan stream during the summer.

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

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

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) female in breeding (nuptial) coloration 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) 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

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

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

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...

Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) crosses over the tail end of a female as part of courtship in an Alaskan stream during the summer; 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...

A female Sockeye Salmon (Oncorhynchus nerka) observes a male, underwater view in an Alaskan stream during the summer.