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Fish and Game Q&A: What happened to the trout fishery in Lake Oroville?

April 8, 2010 |  2:24 pm

Department of Fish and Game crews replant Lake Davis in 2008. In support of the California Department of Fish and Game and its effort to keep hunters and anglers informed, Outposts, on Thursday or Friday, posts marine biologist Carrie Wilson's weekly Q&A column:

Question:What happened to the trout fishery in Lake Oroville? When I moved here in 1974, the fishing for rainbows, browns, king salmon and coho was fabulous. Then Department of Fish and Game quit their stocking of these species. I was told the reason was because there was some disease in the lake that affected these fish (except cohos). If this is true, why doesn’t it affect the trout below the dam since it’s the same water? Could it be that the DFG is using this so-called disease as an excuse to stop planting trout and salmon in the lake? I know they are now planting cohos. I guess we should be grateful for this. But how long will this continue before they tell us that they can’t get any more coho eggs? (Larry P., Paradise)

Answer:The story of why Lake Oroville is now planted with only coho salmon is fairly long and winding. Here’s the account from DFG Associate Pathologist Tresa Veek:

After a stocking program is started, DFG monitors its success through different data collection methods, such as creel surveys and disease monitoring. The rainbow trout that were planted in the 1970s weren’t surviving because of a parasite called Ceratomyxa shasta that thrived in the warm surface water of the reservoir, but was less lethal in the slightly cooler water of the Thermalito Afterbay. So, trout that are meant to be caught within a few weeks are still planted in the afterbay.

The brown trout program was considered unsuccessful because they were hard to catch and so the return to creel was too low to justify continuing the program.

The first coho program began in the 1980s as a net pen operation in Lake Oroville. It was discovered that when fish were grown to larger sizes to meet angler expectations, they developed a bacterial disease that infected their kidneys. To protect other fishery resources, DFG ordered these fish destroyed.

The coldwater fishery program for the lake was then changed to inland Chinook (king salmon) that were planted in the 1990s.This provided a good fishery for several years. Then in 1998 and 2000, Chinook salmon at Feather River Hatchery (which receives lake water) started getting infected with the infectious haematopoietic necrosis (IHN) virus, which killed up to a quarter of the Chinook salmon smolts DFG raised. Also in 2000, the entire inland Chinook program for Lake Oroville became diseased with IHN and had to be destroyed. After much research, it was determined that the virus was being sustained and multiplied by the large numbers of salmon in the lake. The virus probably originated at a very low level in the river that flowed into the lake (created by the Oroville Dam built in 1968) but had been kept undetectable by the lack of good hosts. The disease has always been found in fish below the dam and in returning salmon adults every year.

After more research to determine which fish would not be good hosts for the virus, coho were again planted, but this time, in an effort to avoid the bacterial kidney disease problem, they were raised at the hatchery annex on well water instead of in net pens in the lake.

So far, this program seems to be a success, but Mother Nature is always unpredictable, so the time may come when we have to adapt again, and further complicate the story of fish planting in Lake Oroville.

Q: Is it permissible to relocate pesky squirrels that are destroying or damaging private property? (Fred, Redding)

A: No. Small nuisance mammals that are damaging property may be taken by the owner but may not be released alive except in the immediate area. Relocating nuisance wildlife not only relocates the problem but also places the critter into an area where it has no established shelter or food and water sources, and could potentially spread disease. A depredation permit may be issued for tree (gray) squirrels, unless it is the gray squirrel season, when hunters are allowed a four-squirrel bag and possession limit.

Q:Is it legal to fillet stripers and sturgeon once they are brought ashore?  (George L., Madera)

A:Yes. According to Assistant Chief Rob Allen, all fish (with size or weight limits) in an angler’s possession or when brought ashore must be in a condition where they can be identified and the size and weight determined (Fish and Game Code, sections 5508 and 5509). Striped bass and sturgeon may not be filleted on a boat while in the water, nor can they be brought ashore as fillets (California Code of Regulations Title 14, section 27.65). Once ashore, though, legal-sized stripers and sturgeon may be filleted.

If you have a question you would like to see answered in this column, e-mail it to CalOutdoors@dfg.ca.gov.

Photo: Department of Fish and Game crews replant Lake Davis in 2008. Credit: Debra Hamilton / DFG
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