What is Fish Imprinting?
Fish imprinting is the process of raising fish in a controlled system with water supplied by a nearby river or creek. In this process, sea-run fish such as salmon are brought in from a hatchery as eggs or juveniles and raised in a pond for a short period of time. This allows the fish to become familiar with the water so in 2-5 years they can return to that creek or river to spawn. The imprinting process can help supplement runs in fragile habitats by improving salmon survival in the early stages of life.
Salmon Imprinting Program at Carkeek Park
Every winter the Suquamish Tribe’s Grover’s Creek Salmon Hatchery provides CWCAP with Chum salmon eggs and juveniles to imprint at the Les Malmgren Imprint Pond at Carkeek Park. For several months, these salmon are cared for by shifts of volunteers who feed them, measure their conditions, and interact with park visitors. After about a month, each batch of salmon is released into Venema Creek where park visitors gather to watch them swim down to the Puget Sound. The Les Malmgren Imprint Pond also receives salmon from the Salmon in the Schools program that will be imprinted and released.
Education is the main purpose of Salmon Imprinting at Carkeek Park. Salmon feeding shifts are public and visible to park visitors who can stop by and talk to CWCAP volunteers about the imprinting program. The program also helps supplement the salmon run that occurs at Carkeek Park each fall. This run is exciting for visitors and offers another opportunity to engage with the community about water quality and watershed issues.
If you’re interested in volunteering with the Imprint Pond program, please contact info@CarkeekWatershed.org. The program typically runs from February to May.
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.