Three Steelhead Seen Climbing Fish Ladder

A steelhead seen on the underwater camera

By Daryl Kelley
Three adult steelhead trout were discovered climbing the Robles Fish Ladder on the Ventura River in recent days, the first such sightings of the endangered fish at the ladder in two years, authorities said.
Images of all three trout — ranging in length from 21 to 25 inches — were captured by underwater cameras from last Thursday through Saturday.
The fish were swimming upstream through a $9.5-million fish ladder built to allow them to migrate up the Ventura River around the Robles Dam, which diverts water to Lake Casitas.
The steelhead will now continue their journey upstream, lay their eggs in the gravel in the next month or two, then attempt to return to the ocean, although only about 20 percent survive that round trip, scientists said.
The first steelhead confirmed using the ladder, which did not become fully functional until late 2005, was discovered in early 2006.
But the drought of the last two years dried the river and kept the steelhead from migrating. Now, after a month of good rain, the Ventura River is flowing and the fish have returned to their traditional migration pattern from the salty ocean to the fresh highwaters of the upper river, officials said.
“It’s pretty exciting to see the fish using the ladder like it was intended,” said Scott Lewis, fish biologist for the Casitas Municipal Water District.
The ocean-to-river southern steelhead trout is a unique form of the rainbow trout, which is strictly a freshwater fish. Scientists say the number of steelhead south of Santa Barbara has diminished in recent decades from thousands to hundreds, prompting its designation as an endangered species in 1997.
Only about 100 adult steelhead remain in the Ventura River watershed, federal officials estimate.
It is hard to tell the difference between the two types of fish when the steelhead are young because they are about the same size as the rainbow, Lewis said. But as the steelhead matures during a year or two in the ocean, it consumes far more food than its insect-eating freshwater cousin and grows much larger, he said.
“It’s pretty easy to see the difference,” Lewis said.
For example, the three steelhead seen in recent days were all much larger than the adult rainbow also captured by camera last weekend, he said.
The first steelhead, seen last Thursday, was 21 inches, the second and third, seen on Friday and Saturday, were 25 inches. The rainbow was 13 inches, a little larger than normal for the adult freshwater fish on the Ventura River, Lewis said.
But the key characteristic that quickly confirmed the steelhead sightings, Lewis said, was the size of the large fish’s eye sockets. The steelhead’s eyes are proportionately smaller than the rainbow’s when compared with the size of its body, he said.
“It’s a simple mathematical equation,” he said, “comparing the length of the fish to the eye diameter. The concept is that as the fish gets larger, its eye diameter proportional to its body gets smaller.”
So, while adult steelheads’ eyes are actually larger than the adult rainbows’, they appear to be much smaller, he said.
“It’s like when you look at a human baby,” Lewis said, “its eyes seem so large. But as it grows its eyes seem proportionately smaller.”
Lewis said the eye diameter-to-body length equation is routinely used by fish biologists to determine fish species.
“For the next few weeks we’re going to be out trying to find more,” he said.
This week, Lewis also revealed that lab tests by the U.S. National Marine Fisheries Service on 11 small fish found dead last June after water was shut off during a dam safety test in the upper Ventura River have proved inconclusive on whether they were juvenile steelhead or rainbow trout.
“They’re going to try another method of testing, but that might or might not work,” he said.
It was the largest fish kill on the river in recent memory, Casitas officials said. And it was significant because of how much money and effort has been dedicated to saving the steelhead.
The federal government has required Oak View-based Casitas Municipal Water District to spend $9.5 million to build a fish ladder for the steelhead migration. Casitas must also provide between $1 million and $2 million worth of water a year so the fish can migrate.
A costly federal lawsuit to reimburse the water agency for the expenditures is before a federal court.
A video of the first migrating steelhead of the year may be found on the Casitas Municipal Water District web site at casitaswater.org.