Predatory striped bass ravaging Mokelumne salmon
By Matt Brown
News-Sentinel Staff Writer
Joseph Merz routinely pumps the stomachs of striped bass.
It's not his hobby. It's his job as a fisheries biologist with the East Bay Municipal Utility District.
On one occasion, he found 30 baby salmon in the belly of a fat striper.
"It's amazing to see how many salmon a striped bass can eat," he said.
It is also upsetting.
While striped bass preying on smaller fish has become a problem on the Mokelumne River, there are no plans to limit their population because of their popularity with fishermen.
Trout and salmon fishermen consider them a nuisance and have encouraged biologists to take steps to improve conditions for the smaller fish.
Striped bass, also known as stripers or rock fish, are native to the Atlantic Coast but were introduced to California in the 1880s for commercial fishing. They are anadromous, meaning that they migrate between fresh and salt water. They have large mouths with rows of sharp teeth.
The bass get their name because of the black stripes running horizontal across their silver bodies. They average one to three feet in length but can reach as long as six feet. On the Mokelumne River, they tend to stay in the tidal-affected waters west of Thornton, but many also come up to the Woodbridge Dam.
Occasionally, small stripers will climb the fish ladder and make it upriver as far as Camanche Dam.
Since they found their way into the San Joaquin Delta, the striped bass have feasted upon the bountiful native fish species.
Merz said that on the Mokelumne, up to 40 percent of oceangoing salmonids — steelhead trout and Chinook salmon — are eaten by hungry stripers.
"They have created a problem for our salmonid population," he said. "Whatever they can fit into their mouths they'll eat."
Roger Mammon, a California Striped Bass Association board member, said stripers are popular because they are fun to catch and they are tasty.
"They fight very well," he said. "They are excellent for eating."
Mammon does not think the striped bass population needs to be controlled. He said the poor health of the Delta ecosystem, not the striped bass, is responsible for the decline of other fish.
"There are some people — you may refer to them as purists — who might say there is a conflict of interest," he said. "If it was a healthy ecosystem, purists wouldn't be complaining because there would be plenty of salmon and plenty of trout."
Those anglers who like to fly fish for salmon and trout see the striped bass as a nuisance.
"It's a problem," said Ron Pettit, a member of Delta Fly Fishers. "Obviously it cuts the population down. The bass guys say, ‘So what if the trout are suffering? At least the bass are big and fat.'"
Striped bass love to sit in pools of stagnant water such as at the base of dams and under boat docks. They conserve energy in the calm water and wait for the tasty smaller fish to float past.
Ecologists have taken steps to keep the young salmon and trout out of harm's way.
For example, the rebuilt Woodbridge Dam includes a fish ladder that deposits salmon into the swift current downstream and away from the pool where the stripers prey. This has added to the flourishing salmon population on the Mokelumne, which is back to 16,000 fish from a low of a few hundred in the early 1990s.
"Anytime you concentrate a prey item, that is going to be a problem," Merz said. "We need to find those places and reduce that chance."