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.

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 early summer.

Pink salmon (Oncorhynchus gorbuscha) spawning pair in an Alaskan intertidal stream during the 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.

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

A Pink Salmon (Oncorhynchus gorbuscha) alpha male is attacked by a challenger in an Alaskan intertidal stream during the summer.

Female Chum Salmon (Oncorhynchus keta) sniffing the water where she is building her redd as a male guards.

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

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

Dolly Varden (Salvelinus malma) and one Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) in a deep pool in an Alaskan stream during summer.

Chinook Salmon, also known as King Salmon (Oncorhynchus tshawytscha) in an Alaskan stream during the summer; Alaska, United States of America

Sockeye Salmon (also known as Red Salmon, Oncorhynchus nerka) female excavating her redd while the male guards in an Alaskan stream during the summer; Alaska, United States of America

Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) alpha male contenders (female in background) in an Alaskan stream during autumn; Alaska, United States of America

Male Sockeye Salmon (also known as Red Salmon, Oncorhynchus nerka) digging in an Alaskan stream during the summer. This behavior is considered a displacement activity indicative of the male's frustration in not being able to spawn; Alaska, United...

To encouage his mate to spawn, a male Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) gapes in an Alaskan stream during the autumn; Alaska, United States of America

A male Coho Salmon (also known as Silver Salmon, Oncorhynchus kisutch) bites another for the right to be an alpha male in an Alaskan stream during the autumn; Alaska, United States of America

Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) false spawning melee in an Alaskan stream during autumn; Alaska, United States of America

Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) in the act of spawning in an Alaskan stream during autumn; Alaska, United States of America

Coho Salmon, also known as Silver Salmon (Oncorhynchus kisutch) in the act of spawning in an Alaskan stream during autumn; Alaska, United States of America

Female Coho Salmon, also known as Silver salmon (Oncorhynchus kisutch) being courted by a jack in an Alaskan stream during autumn; Alaska, United States of America

Female Coho Salmon, also known as Silver salmon (Oncorhynchus kisutch) commencing to spawn about to be joined by a jack in an Alaskan stream during autumn; Alaska, United States of America

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