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California evacuates 430,000 trout from too-warm hatchery

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Sacramento County – It was a desperate move to save precious lives – an evacuation of thousands of tiny fish from a state hatchery where they would have surely perished in water that was too warm, all because of the California drought.

On Wednesday, state Department of Fish and Wildlife workers netted the last of the 430,000 steelhead trout fingerlings from the Nimbus Fish Hatchery, trucked them to a boat launch about five minutes away and released them into the American River.

Nobody knows whether the 3-inch-long fish will survive, but they’re expected to have a better chance than they would have had if they had been left in the hatchery tanks, which are filled with reservoir water piped in from the Folsom Dam.

The problem is that, due to the California drought, the Folsom reservoir is only 52 percent of capacity and the sizzling Central Valley temperatures are expected to heat the water to 78 degrees by August, a temperature that would have meant certain death for the young fish.

“That’s too hot for steelhead. We expect they will have a better chance in the river” where they might be able to find cold pools of water, said Gary Novak, the Nimbus Hatchery manager. “The situation is pretty severe. I have to get rid of all my fish and then hope it rains next year.”

The Nimbus Hatchery is one of 22 breeding facilities run by the state that supply most of the salmonids left in the ocean along the Central Coast. These hatcheries raise 30 million to 40 million fish annually and plant them in rivers and streams. The state’s hatcheries were established decades ago primarily as mitigation for dam building, and experts say there would hardly be any salmonids at all swimming in the rivers if not for the breeding program.

From tanks to trucks

The 85,000 silvery fish that were released Wednesday were held in rows of long green tanks in a warehouse. Reservoir water flowed into each tank through a spigot on one side and many of the index-finger-size fish leaped up into the spraying water as workers with nets scooped them up by the hundreds. The squiggling trout were brought in buckets to a tanker truck, which then dumped them through a pipe into the river, where a couple of waiting ducks feasted.

The Nimbus Hatchery harvests eggs and sperm from the salmon and steelhead that swim back to the hatchery starting in September. The fish are identifiable because hatchery workers remove their adipose fins, which are next to the dorsal fin. The fish that were released early also had ventral fins removed so that fisheries biologists can determine how many of them return in three to five years.

Nimbus released all 3.6 million of its chinook salmon three weeks ago so it is now empty, leaving its two managers and six employees with little to do except maintain equipment until next year. All the fish have also been released at the nearby American River Trout Hatchery, which raises rainbow trout for recreational fishing in lakes.

“This (hatchery’s problem) happens to be the tip of the iceberg,” Novak said. “We have the warmest water, (but) with this drought I would assume there is concern at every hatchery.”

Experts, however, said they believe the rest of the hatcheries in California, including the federally managed Coleman Hatchery, will make it through the summer months and into the winter season without having to evacuate fish. But nothing is guaranteed, given that this summer is expected to be one of the hottest on record.

In addition to concerns about warming water, low reservoir levels have left many boat ramps that are used to plant fish high and dry. The state Fish and Wildlife Department bypassed the rivers and planted millions of chinook salmon directly into San Francisco Bay this year because of low stream flows and warming water. That included more than 3 million salmon from Nimbus that normally would have gone into the American River. That could be problematic because steelhead and chinook imprint on the rivers in which they are born and have a higher rate of return when they swim to the ocean themselves.

Usually freed in February

The 4-month-old fish from Nimbus – which officials hope will make up the vast majority of the steelhead that spawn in the river when they return in three to five years – would have been released in February under normal conditions. This week marked the earliest time the hatchery has ever released its steelhead, which must now run a gauntlet of predators, low water flows and hot temperatures in the river before they are ready to swim out to the ocean next winter.

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A fish-eating spider from the Trechalea genus eating a characiform while sitting on a rock in middle of small river in central Colombia. PHOTO: SOLIMARY GARCIA HERNANDEZ

If you want to watch a spider eat a fish—and you know you do—you need to think like a spider.

First, go where the water is still: a windless lake, or a bend in a lazy stream. This is where fish wait for insects to fly close to the surface. It’s a place where the fish feels comfortable. The spider is comfortable, too: Its hind legs anchored on a stone or branch while the front legs rest on the water’s surface. But the spider is ready (and hopefully so are you, with your camera), and the moment the fish’s dorsal fin breaks the surface and makes a ripple, the spider will pounce.

This drama plays out every day, on every continent except Antarctica, according to a paper published today in PLoS ONE by zoologist Martin Nyffeler the University of Basel in Switzerland, who has made his career studying spider behavior.

Apparently, he also has a passion for giving the world more nightmares, because recently his academic output has focused on spiders that eat bats, earthworms, snails, and now, fish. ”A couple of years ago, I started to review the entire spider ecology literature,” he said. “Everything.”

He compiled research from mainstream journals as well as those too old, obscure, or foreign to make it into the arachnophilic canon. After a while, he noticed that non-insect eating behaviors seemed to be more common, and more widely spread, than most spider biologists previously believed. “They all laughed at me and said ‘Spiders don’t eat slugs and snails’,” said Nyffeler. Then he published his review, and the laughter stopped.

In addition to his massive literature review, Nyffeler combed the internet and spoke to fish and spider biologists to gather evidence of fish predation. He contacted the author of each internet picture to make sure the photo wasn’t staged (otherwise he excluded it from his analysis). He also took note which species only caught fish in experiments staged by researchers in the lab or in the field. He didn’t immediately discount these, but was careful to annotate them as such. He also worked with fish specialists, and recruited fish expert Bradley Pusey from Australia’s Centre for Excellence in Natural Resource Management as his co-author.

By the end, he confirmed 89 incidences of spiders hunting fish, spread among 8 spider families. The most prolific were the Dolomedes genus, commonly known as raft spiders. According to the paper, spiders hunt fish most frequently between 40 degrees north and south of the equator. Nyffeler says this is probably because the water is warmer and less oxygenated. Fewer organisms can live in such waters, so fish have to get their food from insects near the surface.

But just because spiders may be hunting fish in a stream near you doesn’t mean it’s easy to catch them in action. One of the wildlife photographers Nyffeler spoke with told him that he had spent over 300 hours taking pictures in the wetlands near Tampa, FL, and had only seen this behavior about a half dozen times.

Nyffeler says across all the fish-hunting spider species, the kill was similar: After pouncing from a stable position, they bite the fish and inject it with neurotoxins. After seconds, minutes, or sometimes hours, the fish dies and the spider drags it somewhere dry, and pumps it full of digestive enzymes. Once the fish’s innards are turned into mush, the spider typically eats everything but the bones. Fish soup, spider style. Yum.

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