From Auke Creek, a flow of information

Posted: Sunday, March 23, 2008

I had lived in Juneau for several years before I even became aware of Auke Creek. Gradually it registered on my mental map as the place where Auke Lake drains to the sea. But that was it - what could be interesting about such a short creek in the middle of an urban area?

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Courtesy Of Mary Willson
Courtesy Of Mary Willson

Bears forage in the creek when salmon are running, and mink regularly forage along the creek. Fish biologists who do research in Auke Creek have built a walkway that runs from near the small hatchery and research building up to the highway bridge.

That walkway is used by four-footed creatures as well: Otters travel along it, leaving their distinctive push-slide, push-slide track in the snow.

Earlier this month I went to Auke Creek to observe the installation of a weir into its permanent framework. Half a day's work for half a dozen people sufficed to put in place all the diverters and baffles that shunt out-migrating juveniles into a trough that channels them into a simple sorting device.

The smallest fish (pink and chum fry) fall into one big vat; middle-sized and larger fish (mostly juveniles of coho, sockeye, dolly varden, plus some cutthroat trout and a few steelhead) are sorted into the next two vats. Stalwart, patient fish-counters stand in the cold water and count the fish in each vat before releasing them to whatever fate awaits them. Occasionally mink and otter plunge into the fish-collecting system and pop out - to mutual astonishment - face to face with the fish counters. Special covers were placed over the counting vats, because opportunistic dippers are all too happy to count a few fry for themselves.

The little hatchery building and the nearby weir are the source of huge amounts of useful information on salmon, dolly varden, and cutthroat trout. Dozens of graduate students have done their thesis work there.

Even more importantly, all the fish, both incoming adults and out-going young ones, have been counted at this weir since it was installed in 1980 (and there are some counts from previous years also). I'm told that no other weirs in Southeast (or perhaps the world!) have such long-term records of total fish migrations both upstream and downstream.

Long-term records are so important, and salmon are so basic to the economy of nature and humans in Southeast, that it is really regrettable that there are so few such records for our region. Decades of carefully recorded data permit the detection of important patterns, such as the response of salmon populations to changing conditions of ocean or climate.

For example, "weir-master" Jerry Taylor has documented that average water temperatures in Auke Creek during the incubation period (fall and winter) of pink salmon have increased over the past 30-odd years. During this period, pink salmon fry have gone to sea progressively earlier and adult pinks tend to return earlier. If these trends continue, the stream may become too warm for successful spawning and incubation, and the early-migrating fry may go to sea before their planktonic prey become seasonally abundant. This reinforces other studies that have predicted a negative effect of climate change and warmer temperatures on salmon in Southeast and raises another warning flag for potential changes that would affect all of Southeast.

The weir is operated daily for eight months of each year. In the late summer and fall, the incoming adults are counted as they are shunted into a small channel beside the weir. The fish counters enjoy seeing unusually lovely dolly varden in breeding colors. They are less thrilled when a big, toothy male chum salmon gets excited; one such male once shredded a fish-counter's chest waders when it leaped up out of the channel.

A good run of sockeye enters this system to spawn in gravels in the lake; this is thought to be a native run, with little or no influence of the rampant translocations that occurred particularly in territorial days. This run appears to be genetically distinct from other runs in the Juneau area.

Coho spawn in all the tributaries of the lake. Some of the young ones spend two years in the system, but others go to sea at age 1. The biggest (and probably older) smolts go out earlier; they survive better and the males commonly return as 'jacks'. Coho jacks at Auke Creek spend only four months at sea and return as sexually mature but small spawners without a big hook-nose. These jacks are only about a foot long and weigh about a pound. In some years there are more jacks than hook-nosed males. They don't usually compete directly with the bigger, older, hook-nosed males but sneak in to spawn beside a breeding pair.

The chum salmon in this system belong to a very small native stock and a large glut of strays from DIPAC hatchery. The native stock comes in later than the hatchery fish, and there is thought to be little interbreeding. Many of the hatchery fish die in lower reaches of the creek. In any case, the Auke system is not very suitable for chum salmon.

Cutthroat trout commonly go to sea, where they (like salmon) gain their adult body size. But they spend varying numbers of years in the lake before doing so. Some go out to sea at a young age and grow relatively quickly in the ocean. However, a few individuals are known to have spent several years in fresh water, growing slowly, before heading out to salt water; it is apparently not known if these individuals spawn while they live in the lake. Cutthroats are not very numerous in this system.

Two kinds of sculpin live in the Auke Creek system. Spiny sculpins are more common in the lake and the intertidal area, and coastrange sculpins are more common in the flowing stream. Sculpins are very interesting and much-neglected fish. Coastrange sculpin can change color, depending on the background color of the stream bottom. They breed in late spring, and the eggs are stuck to the underside of rocks. The male guards the eggs of several females and keeps them well-oxygenated by fanning them with his huge pectoral fins. When the eggs hatch, the larvae go to sea for a month or so, and then come back to fresh water. Sculpins are major predators of salmon eggs, often congregating at salmon runs, and they can dig eggs out of loose gravel. Sculpins, especially the coastrange species, are very skinny in July, before the salmon come in, but by September they are chubby, from a rich diet of salmon eggs.

Relatively recently, motorized use of Auke Lake has increased, raising concerns about possible effects on the organisms that live in the lake. The effluent of inefficient two-stroke engines is known to cause damage to certain fish in other regions. Spiny sculpin in Auke Lake also show signs of damage due at least partly to toxins from engine effluents: Lesions of the liver are more common in Auke Lake sculpin than in sculpin from lakes with little motorized use. I hope that some diligent researcher will also examine the local salmon and dolly varden for possible negative effects of fuels and fuel residues.

There are persistent rumors that somehow the weir has caused a rise in water levels in Auke Lake. Arrant nonsense! The weir is far down the creek, just above the intertidal zone. When in operation, it creates a small pool behind it, but most of the water passes right on through. The top of the weir is way below the level of the culverts that let the creek pass under the highway. It is impossible for this weir to affect Auke Lake water levels - even if a Noah-size flood occurred, it would just destroy the weir.

The Auke creek and lake system has a fascinating history. When the last major glaciers retreated, their meltwaters raised sea levels enough to flood the creek and the lake with salt water. This area was then a bay of the sea. Post-glacial (isostatic) rebound raised up the land and the bay became a salt chuck from about 12,000 years ago to about 6000 years ago. Further uplift raised the system about saltwater influence and it became the freshwater lake and creek system we now have. But evidence of its marine past can be found in the blue clay layers all around the lake and along the creek, where the remains of several kinds marine shellfish are embedded.

Once I looked, I found lots of interesting things in the Auke Creek system, but many of its stories have yet to be told. It is a happening place!



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