Restoration Program

Program Administration

Session: Impacts to Natural Production

Thursday, February 8, 2007 - 8:00 to 9:35 AM

Abundance, habitat selection and potential for fish predation from Common Mergansers on the Trinity River

C. John Ralph, U.S. Forest Service, Redwood Sciences Laboratory, cralph@humboldt1.com, (707) 825-2992
Pablo Herrera, U.S. Forest Service, Redwood Sciences Laboratory, Pablo_Herrera@fs.fed.us, (707) 825-2994
and Sherri L. Miller, U.S. Forest Service, Redwood Sciences Laboratory, smiller02@fs.fed.us, (707) 825-2949

Presentation [PPS - 12 mb]

Previous studies have documented the potential for significant impact upon fisheries stocks by predators such as the Common Merganser. We explored the abundance and habitat selection of Common Mergansers in order to determine the potential predation risk for fish in the Project Area of the Trinity River. We compared the bird survey results from 25 complete river samples from 2002 to 2006 to river habitat types. The samples began in May or June in each year, and continued through the fall. The river habitat types include Riffle, Run and Pool. We divided the river into 16 reaches, made up of a series of segments, resulting in an average number of mergansers per kilometer in each reach in each month. We can compare the abundance of mergansers to the estimates for number of fish from other studies using these river habitat types. Mergansers are most common in the early summer, becoming less common as water levels drop and perhaps as fish stocks change into the fall. From our results, merganser abundance has slightly declined over the period of study. We do not know how fish resources have changed over this same period. However, the usefulness of merganser abundance as an index for increasing fish abundance during the ongoing monitoring in the basin will be discussed.

Presentation notes:

They think they count over 80% of the mergansers. They estimate 200-400 birds live in the 40 miles of river and each eats 500 g/day of fish. This extrapolates to 1-3 million fish per year in the 40 miles and 5 million in the entire river. He recommended modeling abundances with river habitat and comparing to fish data. He noted the need to monitor in spring when the smolts are leaving.

Questions were whether the 500-g/day fish intake was high and whether they are eating salmon or brown trout. Birds eat a lot and 500 g was based on the literature. Juvenile Merganser mortality is due to predation from large fish and hawks.

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Predation by hatchery-reared steelhead on natural salmonid fry in the upper-Trinity River, California 2005

Seth W. Naman, Yurok Tribal Fisheries Program, snaman@yuroktribe.nsn.us, (530) 625-4130, (707) 498-8236

Presentation [PPS - 1.3 mb]

From February to May of 2005 we captured and examined 215 residualized hatchery steelhead and 2,479 juvenile hatchery steelhead in the Trinity River from Lewiston Dam, the terminus of anadromous fish migration, to Old Lewiston Bridge , 3.2 km downstream. We measured each specimen, assessed physical appearance, ranked juveniles as not smolting, transitional, or smolting, performed pulsed gastric lavage, and collected scale samples from 79 residuals, none of which showed signs of ocean entry or ocean growth. We recovered 144 salmonid fry from the residualized hatchery steelhead (mean = 0.701; 95% CI = 0.442-1.095) and 153 salmonid fry from the juvenile hatchery steelhead (mean = 0.062; 95% CI = 0.049-0.077). We used hook and line mark-recapture and snorkel expansion methods to estimate the population of the residuals. The mark-recapture estimate and the snorkel expansion estimate were 1,074 (95% CI = 635-2,024) and 583, respectively. I used an exponential population model to describe the number of juvenile hatchery steelhead that were present each day in the study reach, during the period of study. Using the population estimates, predation rates, and a water temperature based gastric evacuation model, I estimate that the residuals consumed 17,429 (95% CI = 11,007-27,244) naturally produced salmonid fry during the period 28 February-8 May. During the period 28 March-8 May, I estimate the juveniles consumed 295,373 (95% CI = 187,667-439,142) naturally produced salmonid fry in the study reach. These estimates do not include the impact resulting from the consumption of salmonid eggs, predation by anadromous hatchery steelhead, or mortality associated with competition and displacement of naturally produced fry and juveniles by hatchery steelhead. The predation rates described in this study are the highest predation rates by hatchery steelhead on naturally produced salmonid fry ever documented. In order to decrease ecological and genetic interactions between hatchery steelhead and naturally produced salmonids, managers should consider 1) releasing fewer hatchery steelhead, 2) changing fishing regulations in the uppermost 3.2 km to allow harvest of hatchery steelhead, and 3) changing the release location of hatchery steelhead.

Presentation notes:

For the year 2005, 50% of salmon redds above the North Fork occur in the area immediately downstream of the Lewiston Dam. 800,000 juvenile steelhead are released from the hatchery each year. The residual and steelhead smolts ate an estimated 300,000 fry during the study period. This is at least 5% of total fry produced in the study reach, but likely more.

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Fish health data trends for Trinity River Chinook

J. Scott Foott, CA-NV Fish Health Center, USFWS, Scott_Foott@fws.gov, (530) 365-4271

Presentation [PPS - 0.7 mb]

The California - Nevada Fish Health Center , in cooperation with state, tribal, and federal fisheries groups, has conducted diagnostic surveys of both juvenile and adult Chinook salmon in the Trinity and Klamath Rivers since 1991. Early work helped describe the range of parasites, bacteria, and viral agents in the population with particular emphasis placed on Renibacterium salmoninarum (BKD agent) and trematodes (presumptively Nanophyetus salmincola ). Despite being quite prevalent in Trinity salmon, neither pathogen is now considered to be significant heath factors for the basin. Columnaris disease (infection in the bacterium Flavobacterium columnare ) can rapidly increase in the population as water temperatures reach a mean daily temperature of 20 to 21^o C. Along with the protozoan Ichthyophthirius multifillis (Ich), columnaris was a leading cause of the 2002 adult salmon kill in the lower Klamath river. Research has shown that two myxosporean parasites, Ceratomyxa shasta and Parvicapsula minibicornis , are associated with high levels of infection and disease in juvenile salmon rearing or migrating through the Klamath River . While both parasites have been detected in the Trinity River salmon the level of infection is significantly less than that found in the Klamath. The incidence of C.shasta infection in the Trinity River smolts migrating through the lower Klamath was markedly different between 2002 and 2006. This difference impacts on Trinity stocks. Infection data from Klamath River salmon will be discussed for comparative purposes.

Presentation notes:

It is important to understand that infection does not mean disease, as fish can show presence of infectious organisms but be asymptomatic. In the Klamath system, high temperatures and congregation aid disease development. The entire Klamath River is infectious with myxosporean parasites. Chronic exposure to actinospores can eventually overwhelm the fish's resistance. Parivcapsula infections are generally over 80 %. Synergisms are important; multiple infections and high temperatures can lead to high mortality after even limited exposures in the Klamath 1 -3 days. At least 1/3 of the juvenile chinook rearing and migrating through the Klamath River (above the Trinity River confluence) with the have two infections and are at risk of mortality. Trinity River has low C. shasta and has Parvicapsula infection levels. Migration through the Klamath River is the primary disease risk for Trinity fish. However when Trinity River temperatures exceed 20 to 21^o C, risk of columnaris and Ich infections becomes high.

Questions: Habitat of alternate host of myxosporeans, a polychaete, is variable-it is a filter feeder and needs flows with some oxygen. It may be found in fine silt or in Chladophora (type of algae found on rocks) that is difficult to scour. C. shasta and Parvicapsula infection in fish are not seen outside of salmonids. Prognosis for Trinity River Chinook outmigration? It can change yearly and depends on how long they spend in the Klamath River - this year looks good. Are hatchery fish a vector? Not really. Is the timing of out-migration of Trinity River fish significant? Probably not. Klamath River becomes infectious in March-though disease risks (external parasites, bacteria, and myxozoan infections) becomes more severe when daily mean temperatures exceed 21^o C.

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Discussion Session: Impacts to natural production

Panelists: John Ralph, Seth Naman, and Scott Foott

Can you prioritize factors of mortality? IAP is trying to pull all information together and issue of predation has been brought up. It is clear that good survival is important, but we don't know survival year to year. PIT tags might help. Measuring survival is easier than measuring abundance. The need to know mortality was re-emphasized by audience participants.

One problem noted by Foote is that he doesn't have a history of the fish when he captures it - he recommends tagging fish. Isotopes were noted as a way to identify from which basin fish originate, but this is very expensive. When fish are exposed to C. Shasta in low doses, they generally do not do not develop into a disease state. One key thing is that the Klamath River is constantly putting out the actinospores. It is important that fish spend as short of time as possible in Klamath River . If they don't reach smolt size soon, it is worse. Life stages affects on infections? Winter emigrants are healthier than those heading out in the spring.

Brown trout and steelhead management? Where are we headed? Naman recommends reduction of steelhead releases from hatcheries. Year-long effects and competition are likely much bigger effects than the spring predation. Hatchery steelhead are negatively affecting productivity and can't be harvested in the river. Releases could be made further downstream. Fisherman aren't harvesting hatchery steelhead; steelhead return cards indicate they are being released by fisherman. Exact level of residualization is not known. Timing of releases may affect predation.

Brown trout and steelhead management? Where are we headed? Martin recommends reduction of steelhead releases from hatcheries. Year-long effects and competition are likely much bigger effects than the spring predation. Hatchery steelhead are negatively affecting productivity and can't be harvested in the river. Releases could be made further downstream. Fishermen aren't harvesting hatchery steelhead; steelhead return cards indicate they are being released by fishermen. Level of residualization is not known. Timing of releases may affect predation.

How important is predation if there is no habitat to produce yearling coho anyway? Habitat is likely only one limiting factor and we don't want to focus entirely on habitat.

What might be the overall effect of disease in the entire system with removal of dams? The dams congregate fish, regulate flows, and change habitat below the dams. Also dams effect density of polychaetes; phytoplankton and bacteria from reservoirs are food for polychaetes; nutrient from reservoirs affect phytoplankton. So clearly, dams influence disease.

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