Planted fish haven't always fared well at Lake Oroville

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 & Game quit stocking these species. I was told the reason was because there was some disease in the lake that affected the 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 disease as an excuse to stop planting trout and salmon in the lake?

They are now planting cohos. I guess we should be grateful. 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, the DFG tracks its success by different methods, such as creel surveys and disease monitoring. The rainbow trout 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 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 allowed to grow to larger sizes (to meet angler expectations), they developed a bacterial disease that infected their kidneys. To protect other species, the DFG ordered these fish destroyed.

The coldwater fishery program for the lake was then changed to inland Chinook (king salmon) planted in the 1990s. This provided a good fishery for several years. Then in 1998 and 2000, Chinook salmon at the Feather River Hatchery (which gets lake water) started getting infected with the infectious haematopoietic necrosis (IHN) virus, which killed up to a quarter of the Chinook salmon smolts. In 2000, the entire inland Chinook program for Lake Oroville became diseased with IHN and had to be destroyed.

It was eventually 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 gone undetected 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, to avoid the bacterial kidney disease, they were raised at the hatchery annex on well water instead of in pens in the lake.

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

Q: Is it legal to fillet stripers and sturgeon once they are brought ashore?

— George L., Madera

A: Yes. Assistant chief Rob Allen says 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. Striped bass and sturgeon cannot be filleted on a boat, nor can they be brought ashore as fillets. Once ashore, though, legal-sized stripers and sturgeon may be filleted.

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 can be killed by the owner but cannot 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 source, and could potentially spread disease. A depredation permit may be issued for tree squirrels, unless it is gray squirrel season.

Carrie Wilson is a marine biologist with the California Department of Fish & Game. Send quesitons to: CalOutdoors@dfg.ca.gov.