[env-trinity] High Water Spurs Massive Salmon Die Off At Nimbus Fish Hatchery

[Dan Bacher]

High Water Spurs Massive Salmon Die Off At Nimbus Fish Hatchery

by Dan Bacher

Over 60,000 juvenile king salmon per day are dying as a result of  
disease spurred by high water conditions on the American River’s  
Nimbus Fish Hatchery in Rancho Cordova – and little can be done about  
it, according to Department of Fish and Game officials.

“We have lost over one million of the 5 million fish that we were  
raising in the hatchery,” said Bob Burks, assistant manager at Nimbus  
Fish Hatchery. “Before the disease runs its course, we could lose  
anywhere from 50 to 100 percent of the run.”

The fish mortality in the hatchery started when high flows from  
Sierra Nevada snowmelt put a high and unhealthy amount of air into  
the water. The nitrogen over saturation in the water causes bubbles  
to form in the eyes, gills and fins of the juvenile salmon. The fish  
become stressed, just like when a diver contracts a case of the  
“bends” when he/she comes up too quickly to the surface.

Although the gas saturation would have become fatal to some fish, the  
real mortality started when the stressed fish contracted two  
diseases, cold water disease and IHN.

Cold water disease, a bacterial infection, can be treated with  
antibiotics. However, IHN (Infectious Hematopoetic Necrosis),  
formerly called Sacramento River chinook disease, is a virus and is  
not treatable.

IHN is found in the wild, but doesn’t cause the same problems in the  
wild that it does when it infests a hatchery. The hatchery fish are  
more vulnerable because they are crowded in a facility’s raceways and  
ponds. When one fish gets the disease, that fish spreads it rapidly  
to the rest of the population.

“IHN is mainly a threat to the hatchery system, rather than to wild  
salmon and trout,” said Mike Healey, DFG associate fishery biologist.  
“First, the wild fish are generally tougher and more resistant to the  
disease. Secondly, the crowded conditions found in the hatchery cause  
the disease to spread all at once.”

Burks, hatchery manager Terry West and other hatchery staff are  
working day and night to remove the dead chinooks from the runways  
and ponds, hoping that the disease will soon run its course soon.

The flows on the American are normally around 2,500 to 3,000 cfs this  
time of year, but flows have gone as high as 35,000 cfs this winter  
and spring. At press time, releases to the river below Nimbus Dam  
were 11,000 cfs.

Fish pathologists from the DFG are currently trying to determine the  
cause of the IHN outbreak. While the causes are being studied, the  
hatchery ponds and raceways are closed to the public to prevent the  
public from making contact with hatchery water and spreading the  
disease to other facilities. The hatchery visitors center will remain  
open.

If people were to spread the IHN infestation to the DFG’s American  
River Trout Hatchery, located right next to Nimbus Hatchery, it would  
be a disaster for the DFG’s trout planting program in the Sacramento  
Valley region, according to Burks.

One possible source of contamination could be king salmon, kokanee  
salmon and rainbow trout in Lake Natoma and Folsom Lake. After a  
similar IHN infection hit the Feather River Fish Hatchery in Lake  
Oroville in the mid 1980s, the DFG stopped planting chinook salmon  
and brown trout in Oroville, since they were hosts for the IHN virus.  
The Department started planting coho salmon instead because they  
aren’t susceptible to the disease, according to Bill Cox, senior DFG  
fishery biologist.

“At this point, we still don’t know the source of the IHN infection,”  
said Burks. ”If this occurs one time only and it doesn’t spread into  
other years, it won’t have that bad impact upon the salmon  
populations. However, if it continues in other years, it could become  
a real problem.”

Healey noted that the salmonids put in Folsom and Natoma are free of  
IHN before they are planted into the lake, so he doesn’t think it’s  
likely that planted salmon and trout are the cause of the disease.  
More likely sources of the IHN are the sediments that were stirred up  
by high flows or the inadvertent human spread of IHN.

“I’m pretty confident that it isn’t the planted trout and salmon at  
Folsom that are causing the disease,’” said Healey. “The disease  
could possibly come from people walking around the hatchery who put  
their hands in the hatchery water after contact with river water.”

Bill Cox, the DFG’s senior fish pathologist, said there are two major  
areas of investigation in tracking down the source of the IHN virus -  
internal contamination at the hatchery itself and the water supply.

  Even though the adult salmon received at the hatchery are infected  
with IHN, the disease isn’t transmitted to eggs or young fish because  
the eggs are disinfected. “It’s very unlikely that the virus would be  
transmitted this way, since the eggs are treated, although a break in  
procedures is possible,” said Cox.

The second possibility is that the virus is in the water supply. “A  
number of fish species are susceptible to the virus, but the  
principle ones are chinook and kokanee and they go through a rigorous  
process to ensure they are free of the virus before being planted,”  
he stated. “But if there is a break in procedures, there is a  
possibility that infected fish were put in there.”

The DFG will be looking at rainbow trout, chinook salmon and kokanee  
salmon at Folsom to see if they detect the virus in the fish.

This disease infection comes at a time when commercial salmon  
fishermen along the coast are reeling from the impacts of the most  
severely restricted salmon season in history, the consequence of low  
projected salmon returns this fall on the Klamath River caused by the  
Bush administration’s mismanagement of Klamath River water.

The American River is no stranger to fish kills and disease  
infection. Usually low, warm water is the culprit, as during the  
autumns of 2001, 2002 and 2003 when pre-spawning mortality among  
adult fish was very high. In the worst year, 2001, a total of 87,626  
adult king salmon - 67 percent of the run died before spawning.

More recently, many juvenile steelhead in the summer and early fall  
became infected with “rosy anus,” a viral infection.

In spite of the river’s water and disease problems, large numbers of  
chinooks have returned to the system in the last five years – and the  
majority of the fish found in the system are wild spawners.

In Fall 2005, 54,000 naturally spawning adult salmon and 2,842 grilse  
(2-year-olds) returned to the American, according to Healey. An  
additional 20,569 adult chinooks and 1780 grilse retuned to Nimbus  
Fish Hatchery in 2005.

During the previous year, 75,991 naturally spawning adult chinooks  
and 13,756 grilse ascended the river. The hatchery took in 12,741  
adults and 13,659 grilse; an unusual year because the grilse  
outnumbered the adult chinooks.

The impact of the high flows on juvenile chinooks naturally spawned  
in the river is yet to be seen. Many become stranded along the river  
and its floodplain during the high flows, but high flows also wash  
the fish downriver more quickly, away from predators in the river and  
Delta. However, the fish have a higher rate of survival when they  
migrate to salt water as smolts five inches or larger.

Nimbus Fish Hatchery and the American River are significant  
contributors to the Central Valley king salmon population, the most  
vibrant remaining chinook salmon stock on the West Coast. The four  
Central Valley hatcheries produce a total of 24 million salmon per  
year, with Nimbus contributing around 4 million salmon.

“We still don’t know what the high flows have done to the wild salmon  
that were in or emerging from the gravel in the river in December,”  
said Felix Smith, board member of the Save the American River  
Association and a frequent critic of U.S. Bureau of Reclamation water  
policy on the American and other Central Valley rivers. “Do they also  
suffer from over saturation of nitrogen, cold water disease or IHN?  
We do know that numbers of out migrating salmon found in the screw  
traps that the DFG operates have been significantly lower this year  
than in previous years.”

Smith noted that the reservoirs are as much cold sinks as they are  
heat sinks. On rivers below major dams, it takes longer for both the  
river to warm up and cool down. As a consequence, the fish are  
subject to diseases spurred by cold water, such as IHN and the cold  
water disease.

“The terrible thing with salmon is that you can’t go buy some fish  
from somewhere else to raise in the hatchery,” said Smith. “It’s not  
like the case of a cattle rancher who loses 200 cows and replaces  
them by buying more. The question that seems to get lost in the  
discussion is how do you replace the part of the gene pool that’s  
lost? That’s very difficult to do.”

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www2.dcn.org/pipermail/env-trinity/attachments/20060517/32573cc8/attachment.html>