What is Imprinting?
Fish imprinting is the process of raising fish in a controlled system with water supplied by a nearby river or creek. At Carkeek Park we receive salmon eggs and juveniles from the Suquamish Tribe’s Grover’s Creek Salmon Hatchery to raise in the Les Malmgren Imprint Pond. By imprinting them we help improve both their chance of survival and their chance of returning to Carkeek Park when they’re ready to spawn.
Imprint Pond Volunteering at Carkeek Park
For several months in winter and spring, CWCAP volunteers take shifts to feed and monitor juvenile salmon as well as talk with park visitors. The imprint pond also receives salmon from the Salmon in the Schools program to be imprinted and released. After about a month of raising, each batch of salmon is released into Venema Creek in a public event.
The imprinting program is made possible by our partner organizations as well as our wonderful and dedicated volunteers. We are always looking for additional help from any individuals or groups interested in participating.
How does imprinting work?
Salmon have specialized neuro-receptor cells in the tissues associated with the paired nostril area in the upper head/snout area of the fish. These cells play a role in recording the specific chemicals and minerals of their home waters allowing the fish to later find their stream when they near it.
As impressive as chemical environmental imprinting is, it is only effective once salmon are within 30 to 100 miles of their home water systems. Getting close enough requires a sense of the earth’s magnetic field.
Earth has a predictable, consistent geomagnetic field that weakens from the poles toward the equator. Salmon are sensitive to the gradient (change in magnitude) of the geomagnetic field, including the direction of alignment, and can record this pattern information in specialized cell structures. They can then use the earth’s magnetic field like a compass to travel in the direction of their home waters.
Why Chum salmon and not Coho or Chinook salmon?
Chum, along with Pink salmon, enter the estuary (the tidal mouth of a freshwater river or creek where the saltwater tide mixes with the stream) within days of either emerging from their gravelly nest or being released from imprinting facilities. Given the short time that Chum salmon spend in their river or creek as juveniles they can avoid the dry summer months when shallow creek waters cannot provide habitat and food sources. These difficult conditions are exacerbated by the pollution problems faced by urban creeks.
Other salmon species such as Coho and Chinook salmon require 6 months to a year or more before entering the estuary. These species require a suitable long-term freshwater habitat that the Carkeek creeks cannot provide.
How does our imprint system work?
Further upstream of the imprint pond is an intake system that captures water from Venema Creek. Water flows from the intake through an underground pipe into the sedimentation tanks. These sedimentation tanks have screens that capture sediment before the water makes its way into the imprint pond and egg incubator. Vertical pipes in the imprint pond and egg incubator act as spillways allowing excess water to leave the system through tubes out to Venema Creek. When it’s time to release the salmon fry the covered pipes are removed and the salmon are pulled down the drain. The salmon flow through the outflow tube and into the creek.