A recent bacterial outbreak at fish hatcheries in the Eastern Sierra and Southern California has the potential to devastate fish populations around the state.
The bacteria, identified as lactococcus garvieae, was found to be making fish ill at the Mojave River hatchery and has also been detected at the Black Rock Hatchery in Independence and the Fish Springs Hatchery in Big Pine. The findings were confirmed on June 25.
The Hot Creek Hatchery in Mammoth Lakes was quarantined as a suspected fourth site of the bacteria but was later found to be clean,
According to the California Department of Fish and Wildlife, l. garvieae has never been seen in California before. Symptoms of the bacteria in fish include bulging eyes, lethargic or erratic swimming, darkening skin, swollen abdomens and increased mortality. Infected fish can also be asymptomatic, depending on factors like water temperature and stress.
Note: fish-human transmission of the bacteria is extremely rare.
Stocking from the affected facilities has been halted while staff attempts to treat the fish and prevent bacteria spread. Once fish have recovered and the bacteria is no longer a threat to the environment, stocking can resume.
Treatment includes lowering water temperatures, reducing stress related to crowding, antibiotic medication and special diet.
CDFW estimates that the Mojave River Hatchery contains around 860,000 rainbow trout. Ten of the sixteen groups that represent that the majority of Mojave’s fish have been infected.
Early evaluations at Black Rock and Fish Springs suggests that most of the fish in both facilities may be infected. That means 700,000 rainbow trout at Black Rock and 1.5 million rainbow, cutthroat, brown and Eagle Lake trout at Fish Springs. CDFW staff hope that early treatment will prevent an a significant outbreak of the bacteria.
If the treatment is unsuccessful, CDFW will have two options:
1. Demonstrate that the bacteria is widespread in the Eastern Sierra and Southern California, which would allow healthy bacteria carriers to be released with no negative impact.
2: If the widespread presence of l. garvieae cannot be confirmed, the fish will have to be euthanized.
Black Rock and Fish Springs are the source for fish stocking in Mono County.
Waterways throughout southern California have already will not receive any stocking this season. Another 63 lower elevation waterways that would be stocked in the winter will not receive their plant of fish.
In addition, 59-67 roadside waters in Inyo and Mono county that are stocked by Black Rock and Fish Springs are likely to not receive any plants this year.
Making up the plants from non-infected hatcheries would be a time consuming and costly project to undertake. Covid-19 travel restrictions would further hamper the process.
So what happens if the fish are euthanized?
CDFW reports that rainbow trout can take between 10 months and two years to reach a catchable size. Full-scale depopulation would mean no catchable fish ready until December 2020 or January 2021. Based on previous depopulation efforts, CDFW estimates that it could take up to three years to get a hatchery fully back up to pre-infection levels.
In the meantime, the fish available would effectively be wild trout, more wily and coy than hatchery fish. This makes for a harder catch; not impossible but difficult for inexperienced fishermen.
There are additional fears that a lack of easily catchable fish would drive fishermen to overfish traditional catch and release spots like the Upper Owens river.