Faced with a chronic drought, particularly early this year, California has found a way to help its famous chinook salmon to reach the Pacific Ocean despite rivers with too little flow or too hot water: transporting the fry by road, in tank trucks.
The California Department of Fisheries and Wildlife “draws lessons from the last fifteen years of salmon releases and the previous drought to increase the chances of success,” Jason Julienne, head of fish farming facilities in the north of the state.
Salmon are migratory: they are born in rivers, swim to the Pacific when they reach maturity, and can spend up to seven years there, but eventually return to their native waters to breed and die.
“Transporting young salmon in trucks to release sites located downstream has proven to be one of the best ways to increase their survival during dry periods,” said the expert.
The operation, launched in April and which should continue until June, avoids 80 to 150 km of waterways where significant mortality has been observed in the past.
The first transport of fry by road began in the 1980s and is organized every year, but this summer the authorities plan to increase the volume of fish by 20%.
In total, nearly 17 million young salmon will travel in trucks from four Californian hatcheries.
The Feather River hatchery, adjacent to the Oroville dam built in 1967, is customary for this type of operation.
Each year, it alone produces about eight million salmon fry, from the fish that flow naturally and instinctively to this river where they were born.
– 20 million eggs –
It all starts in front of the dam, at the foot of a fish ladder about 1.5 km long, a narrow channel where steps simulate the rapids of a mountain torrent. “The fish will migrate upwards, because it is their instinct to go upstream when they are ready to spawn,” Anna Kastner, head of the hatchery, told AFP.
At the end of May, several dozen of them are already crowding at the top of the ladder, ready to be pushed into a pond of the hatchery where CO2 mixed with water makes it possible to anesthetize the ardor of fish whose larger ones can exceed 22 kg.
They are marked and given an injection of vitamin B1 before being released.
In a few months, once the breeding season comes, the eggs will be extracted from the females and mixed artificially with the semen of the males to fertilize them.
Up to 20 million salmon eggs, placed in trays permanently irrigated by the water of the Feather River, as in their natural environment, will then be stored in the premises of the hatchery, until the fry come out.
These baby salmon are then kept in the open air, in wire basins to avoid serving as a pantry for herons and other predators, until they are large enough to be released into the sea.
“Our survival rate, from when we get the eggs to when we implant the fish, is about 85% to 87%. It is much higher in the hatchery than in the river,” especially during the period. drought where eggs and fry can be under great stress, says Kastner.
The operations of conveying salmon to various sites on the shores of the Pacific, in the bays of San Francisco and Monterey in particular, represent a total of nearly 150 specially adapted tankers.
Since May 10, California authorities have declared a state of drought-related emergency in more than 40 counties. That of Butte, where the Oroville dam is located, is already classified at the “exceptional” level, the highest.
The situation, made worse by the effects of climate change across the western United States, is not expected to improve until precipitation returns in five or six months.
“We want to be sure that we give the best possible chances to the fish, because we don’t know what can happen. We don’t have rain,” insists Anna Kastner.