The first salmon counting weir in Alaska was constructed on the Karluk River in 1921, and every summer since then the weir has provided a remarkable stream of information which has been vital to understanding salmon and successfully managing them.
Counting salmon at Karluk Weir, Sept. 1948
The original Karluk weir was a series of wooden tripods
set across the river with planks laid horizontally between them on the upriver
side. Spaced a few inches apart, the planks allowed water to flow downstream
but prevented fish from swimming upstream. A narrow open section allowed biologists
to count salmon as they swam through.
For much of its length the Karluk River is about a
hundred yards wide and three feet deep, a modest stream compared to other great
salmon rivers. But Karluk Lake, where the river’s sockeye lay their eggs, is an
overachiever, and its huge numbers of returning spawners drew the early attention
of the commercial canning industry.
The first cannery at Karluk put fifty-eight thousand red
salmon into cans in 1882, and by 1901 four million Karluk sockeye salmon were processed,
a number which has never been equaled.
The fish were caught with hand hauled beach seines, a
crude technology by today’s standards. But the nets were pulled across the
opening to Karluk Lagoon relentlessly, one behind the other like the spokes of
a giant paddle wheel, 24 hours a day, seven days a week, and they were deadly
effective. Single haul catches of 30,000 fish were not unheard of, and a single
haul in 1896 took 75,000 fish.
This kind of unbridled resource extraction was common in
the 19th century, and even celebrated, from salmon and buffalo to whales
and dodo birds. Most people then believed God would keep putting fish and
whales in the water no matter how many were taken by humans. As British biologist Thomas Henry Huxley
put it in 1833, “I believe then, that the cod fishery, the herring fishery, the
pilchard fishery, the mackerel fishery, and probably all the great sea
fisheries, are inexhaustible… and any attempt to regulate these fisheries seems
consequently, from the nature of the case, to be useless.”
But as salmon runs in Alaska and the Pacific Northwest
declined, it began to dawn on biologists, and even some canners, that the more
salmon they took the fewer seemed to return in following years, and that some
minimum number had to get upstream for a run to continue.
With this vague notion in mind the Federal government
began instituting various restrictions and even the canners themselves decided
to close the Karluk fishery a few hours a week in the 1890s. Still, by the
1920s, Karluk sockeye catches had fallen to fewer than a million fish a year-
still substantial, but far below the record 1901 season.
At the time no one knew how many spawners it took to
sustain a particular run, or even how many salmon actually went up the Karluk
or any other Alaskan river. It was also not fully accepted that salmon migrate quite
specifically back to the streams where they had spawned.
In this information vacuum, Federal salmon managers were
pulled between conservation minded biologists with unverified hunches and processors
who wanted to can more fish. Since Congress wrote Alaska’s fishing regulations
and the processors had the political power to bend Congress to their point of
view, regulations remained weak and salmon runs kept declining.
In 1918 however, a Russian fisheries professor named Fedor
Baranov wrote a formula which calculated future fish catches as a function of
initial fish population and pressure on that population from natural mortality
and past human fish catches. This revolutionized fisheries management theory but
came with a catch- it required knowing how many fish there were to begin with.
But since fish usually swim where they cannot be easily seen or counted, this was
not a simple thing to determine.
Fish populations can be estimated by tallying catches
and doing surveys with hooks or trawls or pots or today, sonar. But catches and
surveys provide only a statistical estimate of how many fish there were before
the catching started, and if this initial population of fish is overestimated,
or the estimated percentage of that population which can be sustainably caught
is too high, they can be overharvested, leading to a population crash. If
you’ve lived in Kodiak long enough you’ve seen several once abundant fisheries
managed this way go bust, including shrimp and king crab.
But salmon, unlike almost all other marine fishes except
for eels, migrate up rivers, and when channeled through weirs can be counted
with great accuracy. This allows Baranov’s formula to be successfully applied,
and the weir counts on the Karluk allowed salmon biologists to do just that.
Once they knew how many fish swam up the Karluk in any
given year, biologists could add the number caught by fishermen and then
compare that total number to the number of fish returning in following years. This
gave them a very good idea of how many spawners it took to produce a given
number of returning fish, and therefore how many fish had to escape past
fishermen to maintain a long-term run. And because salmon can be counted every
day as they pass through the weir, fish managers could track daily fish counts against
the historic data to sustainably manage the fishery day by day.
Hundreds of weirs were eventually installed in rivers
all over the state and since 1959, when ADF&G managers began using weir
data to manage salmon, that system has proved remarkably successful, first to rebuild
Alaska’s salmon runs, and then to maintain them.
Weirs make it relatively easy to manage fishermen and overfishing
has been regulated out of existence in most areas of the world where salmon
historically returned in great numbers, including Alaska. However, the
incremental destruction of spawning habitat with dams, roads, parking lots,
houses and irrigation systems is exquisitely hard to manage and is now the main
threat to remnant salmon populations in Northern Europe, Japan, New England,
and the Pacific Northwest.
Indeed, as Alaska’s urban population grows, this may be
happening now in the Mat-Su Valley. Even as commercial fishing in Cook Inlet is
constrained, growing suburban sprawl, plus predation by invasive pike
introduced by humans, may be driving the decline of salmon numbers there.
Weirs helped Alaskans keep our salmon runs strong for a
long time, and in places where the human footprint on spawning lands is slight,
they will continue to be useful in controlling fishing effort. In the coming
centuries however, as humans take more and more land away from salmon in Alaska,
and as chemicals from our global civilization drain into the ocean salmon swim
in, how we keep salmon runs alive in Alaska remains to be seen.
This article first appeared in the Kodiak Daily Mirror January 13, 2021
Key Sources:
Gard, Richard, and Richard Lee Bottorf, A History of Sockeye Salmon Research, Karluk River System, Alaska,
1880-2010, U.S. Department of Commerce, 2014
Orth,
Don, The Overfishing Problem,
https://vtichthyology.blogspot.com/2019/09/the-overfishing-problem-by-don-orth.html
Roppel, Patricia, Salmon
From Kodiak, Alaska Historical Commission, 1986
Fedor Baranov https://en.wikipedia.org/wiki/Fedor_Baranov#The_catch_equation