Salmon eggs harvested
Spawning season keeps Mokelumne hatchery busy
‘Tis the season for spawning. November marks the middle of the spawning season for Chinook salmon, which swim upstream on the Mokelumne River from the Woodbridge Dam to the base of the dam at Lake Camanche.
It’s there that the California Department of Fish and Wildlife and East Bay Municipal Utility District workers hope to take 7.5 million eggs and produce 6.8 million smolts by the end of the spawning season in December, Mokelumne River Fish Hatchery Manager William Smith said during a tour of the hatchery on Thursday morning.
“We’re having a good, above-normal season. We’ll probably see around 14,000 to 15,000 fish in the river this season. Last year the count was around 18,000,” Smith said.
Female salmon prefer to lay their eggs in the gravel at the river bottom, but because of the dam at Lake Camanche there is little gravel available to them. A fish ladder diverts them to the south edge of the river and leads them to the hatchery just west of the dam.
Their ability to bypass the fence is hindered by a mechanical gate that controls access to the trap, a necessity as the tight quarters of the collection area could agitate the fish.
A fish guidance fence controls the amount of fish that can flow to the fish trap at one time. Most salmon gather at the fence by the hundreds, attempting to swim upstream towards the trap because the water barrier mimics the current of a waterfall, which the salmon can swim up when they are in the wild.
“Some of the smaller fish can make it over the fence, but they are usually much smaller,” Smith said.
Once the determined salmon make their way through the gate, they swim up a narrow ditch to a gathering tank, where a mechanical fish crowder herds them into the hatchery building.
Inside the hatchery building, a dozen CDFW employees wait for the salmon to follow the ladder into a building that resembles a manufacturing plant.
Once inside, employees separate the salmon by gender (males go on the left chute, females to the right), and determine whether the fish are ready to spawn.
Smith said the females have rounder snouts than the males, who have hooked upper jaws, thinner bodies and are usually brighter in color.
The hatchery has an egg count goal of 750,000, and a daily fish target of 600 salmon.
“We only spawn twice a week, and we process about 150 to 200 females a day, which gets us about 700,000 to a million eggs a day,” Smith said.
The fish that are not ready to spawn are thrown down a chute — again separated by gender — and checked five days later to determine if they’re ready to spawn, Smith said.
Salmon that are ready to spawn are immediately killed. It’s a five-step process performed in assembly-line fashion.
According to Smith, the salmon are given an electrical shock so they won’t feel any pain before being killed.
Employees known as gutcutters strike the males on the head with rubber mallets and sever the spinal cords of the females. If a fish wiggles its fins, they are usually hit again. Workers rinse the blood out of the fish with a hose.
“If the blood gets into the pan with the eggs, the sperm can’t get in,” Smith said.
A worker, using a sharp razor blade, slits open the female salmon’s stomach. Another worker takes a male salmon and squirts sperm into the female’s stomach cavity. Then the eggs are poured into a plastic pan.
Depending on the size of the salmon, each female produces 3,000 to 5,000 eggs.
Once the sperm is sprayed onto the eggs, the eggs are fertilized in fresh water. Once fertilized, the eggs go into a bucket of iodine for 20 minutes, which is done to kill bacteria, Smith said.
“Then they are rinsed in fresh water for an hour, a process that removes the iodine and hardens the eggs. Then the eggs are placed in racks filled with fresh running water and later into hatching jars,” Smith said.
Fish with tags are separated by scientific aids with the CDFW. The aids then take a scale sample from the salmon and decapitate the salmon using a guillotine before tossing its body into a container of ice.
“We will be taking the heads back to our laboratory (in Sacramento) where we will extract the coded wire tags located in the soft tissue of their snout. We read the numbers of the tag which correspond to a hatchery code,” said Sarah Sanders, a CDFW scientific aid.
Sanders said the hatchery codes tell what part of the world the salmon are migrating from.
“Last week we read a code from Canada,” Sanders said.
Smith said it is not uncommon to get salmon from warmer waters around South America.
“We’ve seen a few tags from Columbia,” Smith said.
After tag numbers have been collected, senior scientists with CDFW compile the data and present the figures at the annual salmon information meeting in Santa Rosa.