Coho Salmon

Coho Salmon (Oncorhyncus kisutch)

Coho Salmon are one of three native anadromous salmonids that remain in the Russian River watershed. Coho populations along the Pacific Coast have been categorized into seven distinct Evolutionary Significant Units (ESU). Russian River coho are part of the Central California Coast (CCC) ESU, the southernmost population. As recently as 1952, the Russian River Watershed had runs of 15,000 plus coho salmon and 45 years later they were nearly extirpated from the system! CCC coho were listed as a threatened species in 1996 and upgraded to endangered in 2005.

In 2001, the Russian River Coho Salmon Captive Broodstock Program was formed to help restore a sustainable population of wild coho salmon to the watershed and nearly two decades later hundreds of coho are returning every winter.


Life History

  • Coho begin their lives as eggs hidden under gravel in a nest known as a redd and incubate for 30-60 days, depending on water temperature.
  • After hatching they hide in gravel for 2-10 weeks and emerge as young of the year, aka yoy. Yoy can remain in their natal creek for up to a year, where they begin to prepare to return to the ocean.
  • After a year YOY become smolts through a process called smoltification, their bodies undergo a series of physiological changes to prepare for the transition into salt water.
  •  After smolts migrate out to the ocean they begin their adult life, where they will remain until they return—usually as three year olds.
  • There are exceptions where some fish return in their second year. These are usually precocious males called “Jacks”, but can also be females known as “Jills”.
  • Coho rely on fall rains for access to spawning streams. Once in fresh water, coho stop feeding and their bodies change to prepare to spawn.
  • Coho pair up, the female digs a redd, they spawn then die. Their bodies can provide essential nutrients for the creek and even their offspring!

Here is a more detailed overview of the coho salmon life cycle.

Identifying Characteristics

Juveniles​

  • Sickle shaped anal fin, often with white leading edge
  • No spots on their dorsal or caudal fins
  • Large, clear eye with no markings on the perimeter
  • Parr marks are tall and slender with more space in-between than steelhead
  • Smolts lose their parr marks and turn silver


Coho salmon young-of-the-year (yoy)
Coho salmon smolt

Adults

  • Silver sides while at sea, with blue green back
  • Roundish spots on their back, dorsal fin and top of their caudal fin
  • Mouth is dark with a white gum line at base of teeth
  • Males in spawning phase develop a hooked jaw called a “kype” 
  • Both sexes change colors during spawning to have dark heads and increased red pigment on their sides, more pronounced in males
  • Typically grow to 60 cm and weigh between 7-11 pounds


Adult coho male in spawning phase
Adult female coho in spawning phase

Habitat

  • Smaller coastal streams and tributaries to larger systems like the Russian River
  • Needs:
    • Cold (<20°C) clean, year-round water
    • Diversity of instream habitats (riffles and pools)
    • Complex cover like large woody debris and deep undercuts to hide in
    • Abundance of spawning gravels with low amount of silt
    • Densely-vegetated riparian corridors to provide shade, erosion control, nutrients and woody debris
    • Low to moderate gradient streams without migration barriers

Fun Facts

  • Coho salmon naturally have the widest range of any salmon. Historically they were found in coastal streams from North Korea all the way to California!
  • After sockeye, coho spend the most time in fresh water of all salmon species
  • Coho can leap vertically more than 6 feet

References and Recommended Readings