It's been accepted for years that salmon get their homing cues from the
water chemistry of their home river. This occurs during the month or so
before they undergo the physiological transformation called smoltification,
when their bodies change to silver color and they develop the ability to
maintain a lower bodily salt concentration relative to the water around
them, as they'll need to do once they reach salt water. But coded-wire
tagging studies have shown us that homing is more than chemistry-based.
There are also genetic components.
To show the genetic effects on stream homing of salmon, I want to relate the
results of a study I worked on a few years ago where I looked at the stray
patterns of coho salmon released from Agate Pass Seapens near Seattle.
These pens had been in operation for 15 years, and almost all years' had
coded-wire tagged fish, so I had a fair amount of data to work with. Over
those 15 years, the hatchery had used broodstock from 3 hatcheries in 3
different locations: (1) Wallace Hatchery in the Skykomish River (that river
is 20 miles north of Seattle and the hatchery is at least 30 miles
upstream); (2) George Adams Hatchery in southern Hood Canal (Hood Canal is a
body of water parallel to Puget Sound with its own drainage basins); and (3)
Minter Creek Hatchery in Puget Sound sort of near the net pens. An
important fact is that George Adams and Wallace hatcheries are not close to
the net pens.
In every case, no matter the broodstock source, the handling of the eggs and
fish were the same. They occurred like this: Eggs were transferred to
Minter Creek Hatchery from their originating hatchery, hatched there, and
the fry were reared at that hatchery for a few weeks. The fry were then
transferred to another hatchery for several months of overwinter rearing,
and then transferred to the saltwater net pens for about 6 months of
additional rearing and subsequent release.
In spite of the fact that some of these fish had never been in their home
stream, a few adults originally from Wallace and George Adams hatcheries
returned to those hatcheries. Also, the ONLY adults that returned to these
distant hatcheries from the net pens were ones that were originally from
those individual hatcheries, so these weren't random strays. This might
sound confusing the way I explained it, so sorry. Anyway the whole boring
report is at http://home.att.net/~thirdwind/agate96.pdf.
-- Jay DeLong Olympia, WA
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