Friday, January 24, 2020

Smeltdown: Small Fish Continues Vanishing Act (Repost)

Hey everyone, I'm posting this article about the Lake Erie rainbow smelt population from the Detroit FreePress because it related to a walleye article I'll be posting soon.   To see the original Free Press article Click Here!

Tom Durecki remembers the glory days for smelt fishing — or smelting — in Michigan in the 1970s.
"The smelt are running!" was a call that sent fisherman scrambling to Michigan rivers and streams to dip nets and catch buckets full of the silvery fish as they moved into tributaries to spawn at the onset of spring — right around this time, every year.
"It was absolutely fantastic," said Durecki, owner of Tom's Bait and Tackle Shop in East Jordan. "Even into the '80s, we'd go up to Carp River in the U.P. and you'd get what you wanted in an hour — five, 10, 15 gallons."
Those days are gone. The smelt population has declined so much, so quickly over the past two decades that most anglers don't even bother trying anymore.
Why it's occurring isn't simple to explain. Researchers said they think the arrival in the Great Lakes of invasive species like zebra mussels disrupted the food chain and plays a role. But it's not the entire answer. Adult smelt today are almost a third smaller than they were less than 40 years ago.

Even more puzzling, a new study shows smelt hatchling survival is improving, but it doesn't seem to impact the dwindling adult population.

The smelt's plight matters, researchers said, because smelt are an important food source for some of the sport fish that drive Michigan's multibillion-dollar fishing tourism industry.

They also can tell scientists key things about the Great Lakes through their behavior, such as about water temperatures that contribute to harmful algae blooms in Lake Erie.

"People ask about it every spring: 'What happened to the smelt?' " said Michigan Department of Natural Resources fisheries biologist David Clapp, who is based in Charlevoix.

There's no simple answer, and the mystery in some ways is deepening.

"Trying to explain it is not that easy," said Chuck Madenjian, a research fishery biologist with the U.S. Geological Survey's Great Lakes Science Center in Ann Arbor.

"There's nothing really that obvious about what's driving that pattern."

Invasive species
Like so many fish people associate with the Great Lakes, the rainbow smelt is an invasive species. The approximately 6-inch fish is native to the Atlantic and Pacific oceans, but moves into freshwater to spawn.

It was first stocked in Crystal Lake in Benzie County in 1912, after several unsuccessful attempts to stock smelt in the St. Mary's River to support another transplanted fish, Atlantic salmon. Smelt were found in Lake Michigan in 1923 and then spread throughout the Great Lakes.

Smelt quickly thrived in their new freshwater home. The commercial harvest of smelt on the Great Lakes reached 4.8 million pounds by 1941. The population showed large fluctuations over the years, impacted by lamprey eels and the emergence of whitefish and lake trout.

Some 94% of smelt harvested from the Great Lakes come from Lake Michigan — on both the Michigan and Wisconsin sides. It was around 1993 when smelt stocks began to plummet.

The Great Lakes Science Center does annual prey fish surveys in the lakes, trawling the lake bottom and counting what they find. Their 2013 survey found 11 juvenile smelt — smelt less than a year in age — per hectare, an area of 10,000 square meters. That was only 6% of the long-term average count.

"Rainbow smelt biomass in Lake Michigan during 1992-1996 was roughly four times higher than rainbow smelt biomass during 2001-2013," scientists from the Science Center wrote in a report on Lake Michigan prey fish populations last year.
Clapp pointed out that the start of the decline coincides with the arrival and spread of zebra mussels in Lake Michigan.

"That changed the reproductive and nutrient dynamics of the lake," he said.
Smelt eat zooplankton, small aquatic shrimp-type creatures, and they have declined significantly over the same time period, Clapp said.

But that's not a perfect answer, Madenjian said.
"We don't know why smelt would be affected, but not a lot of other species," he said.

The take by anglers also doesn't fully explain the drop, Madenjian said. Nor does larger fish, such as salmon and lake trout, preying upon smelt, he said.

"The amount of predation on them by salmon and trout was bigger in the 1980s than the 1990s, and yet the big drop was in the 1990s," he said. "You begin to doubt that predation was a driver."

The plot further thickened with research out of Purdue University that shows smelt offspring survival is rising in Lake Michigan, but with no impact on the adult population of smelt, which are now on average 2 inches shorter than they were in the 1970s — down to about 4.5 inches in length.

"Traditionally, the ratio of the number of offspring that survive and the number of adults that are around is pretty constant," said Zachary Feiner, a doctoral candidate in Purdue's Department of Forestry and Natural Resources, who was part of the research team.

"We saw that the number of offspring was increasing. It was really unexpected, especially since adults are smaller, so they should be laying fewer eggs, and laying worse eggs.

"We really don't have an answer for it."

One theory: Smelt are known to engage in cannibalism on their hatchlings. With fewer adult smelt, the juveniles have a chance to thrive.

As scientists continue to seek answers, Feiner outlined why it matters.
"Smelt, alewives, they were invasives. Now they're supporting a multibillion-dollar fishery," he said. "These are the forage fish at the base of the food chain."

Smelt also illustrate how the smallest plant and aquatic life in the Great Lakes are changing, Feiner said. And as a fish that likes colder water, they can show how stratification — changes in a lake's water density and temperature — is changing on Lake Erie, where algae blooms have sparked drinking water crises in recent years.

"Smelt can be a canary in the coal mine in a few ways," he said. "They can tell you what's going on in the environment."

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