Coho Salmon (Oncorhynchus kisutch) in the act of spawning in an Alaska stream during autumn.

The male Sockeye Salmon (Oncorhynchus nerka) of the spawning pair being aggresive by gaping, Southcentral Alaska

Coho Salmon (Oncorhynchus kisutch) in the act of spawning in an Alaska stream during late autumn.

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

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

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.

A Pink Salmon (Oncorhynchus gorbuscha) sneaker male courts a female building her redd while the alpha male is away fighting in an Alaskan intertidal stream during the summer.

Headshot of a Coho Salmon (Oncorhyncchus kisutch) alpha male (foreground) and his mate reflected in the the shallow water of their spawning habitat in an Alaska stream during late autumn.

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

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

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

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

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

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