While her alpha male guards downstream, this female Sockeye Salmon (Oncorhynchus nerka) uses her anal fin to probe her redd in an Alaskan stream during summer.

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

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

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.

Male Coho Salmon (Oncorhynchus kisutch) threatens with a gape while female is at the side of the creek in the background, Southcentral Alaska

Sockeye Salmon (Oncorhynchus nerka) spawning pair just upstream of a culvert (in background) in Alaska during late spring. The female has a putative lamprey scar.

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.

While her alpha male guards downstream, this female Sockeye Salmon (Oncorhynchus nerka) uses her anal fin to probe her redd in an Alaskan stream during summer. Underwater view in an Alaskan stream during the summer.

A male Sockeye Salmon (Oncorhynchus nerka) holds a position high over a redd site as the female approaches from downstream in an Alaskan stream during early summer.

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

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

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 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 Alaska stream during the summer, South-central Alaska; 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

Young girl holding a salmon in a set-net skiff, South-central Alaska; Seldovia, Alaska, United States of America

Young girl holding a fresh caught salmon while in her family's set-net skiff with her mother, Seldovia, South-central Alaska; Alaska, United States of America

A Sockeye Salmon (Oncorhynchus nerka) jack courts a female in the absence of the alpha male, Southcentral Alaska