May 9th - Coho Runs

It is very interesting to see the different salmonid life history patterns.  As the last of the chum leave the estuary we are seeing a surge of Chinook and coho sub-yearlings, as well as yearling coho (wild and marked).  The wild yearling coho predominately leave the the estuary beginning in April through June, while the sub-yearlings will stay within the estuary.

The below graph shows fork lengths of coho hatchery and wild yearlings, as well as sub-yearlings.  A "marked" salmon is a hatchery fish "marked" by the removal of the adipose fin.  The hatchery salmon are released in April-May and by June have already left the estuary and surrounding rivers.   A interesting point to make is the difference in behavior between wild and hatchery coho. The hatchery coho immediately leave the estuary whereas the wild coho remain through June.  This illustrates that while the fish are genetically similar their behavior and responses to environmental stimuli are different then their wild counterparts.

 

Graph obtained with permission from the WFC 2011 Annual Report