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

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

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

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

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

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

Female Sockeye Salmon (Oncorhynchus nerka) makes a dig while alpha male guards downstream in an Alaskan stream during summer.

Three male Sockeye Salmon (Oncorhynchus nerka) competing to spawn with one female during early summer in an Alaskan stream.

Male Coho Salmon (Oncorhynchus kisutch) responding to the female's probing by gaping, underwater view in an Alaskan stream during autumn.

Female Coho Salmon (Oncorhynchus kisutch) probing behavior induces the male to false spawn, underwater view in an Alaskan stream during autumn.

Dolly Varden (Salvelinus malma) male underwater in an Alaskan stream during autumn.

Mature male Chum Salmon (Oncorhynchus keta) size each other while competing over a female 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

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) 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 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,...

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

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