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Disease and Chinook

by Siskiyou County supervisor Marcia Armstrong 2/18/05

This year's Chinook salmon run was a disappointment. At the latest Klamath River Basin Fisheries Task Force meeting, it was reported the returns to the Klamath were estimated to be 88,777 fish with a 10% early spawner
(grilse or "jack") component. This was well below the predicted return level of 98,600 fish. Of returning fish, an estimated 24,246 were "natural spawners." This was considerably below the 35,000 threshold for returning natural fish (or "escapement") established in connection with fishing quotas.

The Shasta River had an estimated chinook run of 833 fish ( 13.4% grilse;) the Scott had 445 fish (4.7% grisle;) and the Salmon River had 626 fish
(15.3% grilse.) Bogus Creek saw about 3,700 fish compared to 15,000 last year. About 24.6% of these were estimated to be of hatchery origin. It should also be noted that the grilse portion of the run is often looked upon as an indicator of the health of next year's run. (Chinook salmon return to spawn at a variety of ages from 2 year old grilse to five year-olds.) It was reported that the ocean reaches its highest cyclical productive phase for salmon next year, so there are hopes for better runs next year.

In the Scott River, it was observed that the three-year aged old portion of the run was just about gone. Looking back to 2001 when these fish were juveniles, there was a serious incidence of disease in the "mainstem" Klamath River that may have effected the Scott River run.

There is a considerable amount of fish counting that has been done on Chinook salmon over many years. This is because of the value of the fish to commercial, sports and tribal interests. A substantial amount of funding is spent on fish counts used to project the following year's run for use by the Klamath Fisheries Management Council in allocating fishing quotas. Chinook also return early in the season when the rivers are at a level where fish counts can be done.

Up until very recently, information about the federally and State listed coho salmon has been generally limited to whether the fish were either present or absent in a stream. As coho spawn later in the season when flows are high, it is more difficult to get estimated fish counts. When the Department of Fish and Game reviewed coho documents during the State listing process, they determined that about 1,400 streams had been sampled. Of these streams, coho were documented to be present in about
500 of those streams.

Unlike Chinook, Coho return regularly at age three to spawn. This creates a series of three "brood years." In any stream, one brood year may be good and another may not have any fish. A thorough "presence and absence" survey would include a series of several three-year sets. Unfortunately, historic surveys were incomplete and there is minimal information in most areas.

Danielle Quigley reported on data received thus far from this last season's 58 river mile Scott River coho survey. This survey ran from the confluence of the East and South Fork of the Scott down to its confluence with the Klamath River. The survey observed 1,567 live fish, 578 carcasses and 958 "redds" or nests where the coho had deposited eggs. In the past, the biggest barrier to spawning had been a disconnect between the tributaries and the Scott River. This year, almost all tributaries were connected by the first week of December. Coho were able to into the lower reaches of Shackleford and Patterson Creek, as well as French and Sugar Creek. Unlike the prior two brood years, indications are that this was a great year for coho.

Scott Foott and Jerri Bartholomew gave a briefing on their studies of fish disease. Three main diseases are affecting our fish - ceratomyxosis
(C-Shasta;) columnaris (gill rot) and parvicapsula (kidney disease.). "C-Shasta" is a spore that needs a worm (or "polychaete") as part of its life cycle. In 2004, it was estimated that 45% of the juvenile chinook in the Klamath River at peak out-migration were infected with this fatal disease. (Local steelhead have some immunity. No studies have been done on the susceptibility of coho.) 94% of the juveniles were found to be infected with parvicapsula.

Scientists sampled a range of locations in the Klamath system for C-Shasta last summer. The infected worm was found in the mainstem Klamath and as high up as the Williamson and the Sprague, however fish mortality increased substantially in the river below Iron Gate dam. It appears that the reservoirs provide little habitat for the host worm and the spores dilute out. The worm appears to like nutrient rich areas, fine silt or sand, eddies, and where mats of algae (chlodophora) or fresh water sponges are found. Fish cannot infect other fish. They can only be infected through exposure to the worm.

Fish coming out of the Scott, Shasta and Salmon Rivers were found not to be infected until they reached the Klamath. Some "hot spots" were identified. Fish left in cages for six hours at Beaver Creek, taken back to the lab and placed in clean water were found to have a 90% mortality.

This research is very significant. It means that disease could be the major factor in recent chinook fishery declines in the Klamath system. I think coho susceptibility studies should commence immediately.

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