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|Fish are struggling for food in Lake Huron|
|Written by The Bay City Times|
|Thursday, 06 March 2008 02:25|
Walleye are doing well in Saginaw Bay, but only because they're eating another sport fish: yellow perch.
"We think it's related to exotic species like the zebra mussel, quagga mussel, round gobies and the spiny water flea."
Scientists are still trying to figure how the shortage will affect future sport and commercial fishing here.
For now, the latest findings are from a prey study by Roseman and others, expected March 19 at a Great Lakes Fishery Commission meeting in Niagara Falls, Ontario.
Roseman thinks the latest research, based on trawling surveys last year in the outer bay and lake, is partly positive.
That's because collections from 2006 to 2007 showed an overall increase in total prey biomass, or food for larger fish. Researchers extrapolate from their trawling surveys that total prey biomass increased from 32 kilotonnes to 40 kilotonnes, or by about 18 million pounds.
That increase was mostly due to high numbers of small bloaters, or chubs, and evidence of bloater "recruitment," or small bloaters becoming adults.
The density of juvenile bloaters also nearly doubled from 2006 to 2007, reaching a record-high level, according to the survey. That makes five years in a row that researchers have found an above-average number of juvenile bloaters in the lake.
The abundance of rainbow smelt also increased by about 15 percent, according to the survey.
The bottom line, Roseman said, is that bloaters and smelt may be beginning to replace the void left by alewives when populations of that forage fish crashed in 2003 and 2004.
Jim Johnson, a research biologist for the state Department of Natural Resources, thinks it's too early to celebrate.
Johnson, who works at the Alpena Fisheries Research Station, said the smelt and bloater numbers are just an "uptick" for now. He's seen similar "blips" in prey numbers that weren't sustained.
There's been a steady decline in prey availability in Lake Huron since 2000, Johnson said.
"The graph looks like the tail of a dog," he said. "It's dropping down and the very tip curves up.
"It's not a rebound, but a slight turning in the trend."
One concern is that the smelt, at 1-2 inches long, are still a pretty small fish, and not big enough to grow nice-sized salmon and lake trout and divert predators from eating state-stocked fish, which are the size of alewives, Johnson said.
The current prey shortage in Lake Huron can be traced back to 2003 and 2004, when alewife populations collapsed due to a number of factors, including a couple of hard winters and interactions between exotic species like the zebra and quagga mussel, spiny water flea and round goby, Roseman said.
EPA data also show that around 2003, the same time alewives disappeared, there was a sharp decline in the offshore production of zooplankton big enough for alewives to eat, Johnson said.
"That's why the alewives won't come back," he said.
"I saw seven of them last year. We got them in some gill nets in Thunder Bay ...
"In 1995, we had one net that had 3,000 alewives in it."
Changes in the Lake Huron fishery have caught the attention of the scientific community and garnered political support for more research, including a $4 million ecosystem study to take place this year by the National Oceanic and Atmospheric Administration.
"We're kind of in the middle of a whole bunch of new science going on in Lake Huron," Roseman said.
"And in coming years, we will get lots of the results of what's happened since alewives left the picture. It's kind of like a giant experiment that happened naturally."
Conditions in Lake Huron depend on where you are, Johnson said.
"Saginaw Bay is the best walleye fishery in Michigan," he said, based on DNR numbers. "It's fantastic. It's among the best walleye fisheries in the country" along with Lake Erie.
But the Saginaw Bay walleye population has recovered because walleye are mostly eating yellow perch, Johnson said.
The fishing conditions are worse in offshore areas, he said.
That's because salmon are mid-water feeders. They're looking for alewives and finding just bloaters and smelt, in smaller numbers than previous alewife populations.
"Yes, we're all hopeful that uptick is sustained next year," Johnson said.
"I'll be a lot more upbeat about this if you call me next year and they're reporting another year of rising prey biomass."
Once the USGS study is presented, it should be available online at www.glsc.usgs.gov.
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