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.
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 100 yards wide and 3 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 50,000 to 80,000 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 1 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.
Toby Sullivan is executive director of the Kodiak Maritime Museum.