Netting Fish
Fish managers for the Wyoming Game and Fish Department in Pinedale net fish for a population estimate on the Green River near Daniel earlier this summer. Photo by Mark Gocke, WGFD
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Brown Trout
A nice brown trout is returned to the water after being weighed and measured by fish managers from the Wyoming Game and Fish Department. Photo by Mark Gocke, WGFD
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Mottled sculpin
A mottled sculpin, one of the many important nongame fish found in the Green River. Photo by Mark Gocke, WGFD
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Green River fish numbers look good
Annual river check-up to check fish populations
by Wyoming Game and Fish Department
November 17, 2008
(Pinedale) – Fish biologists with the Wyoming Game and Fish Department in Pinedale performed their annual "check-up" on the Green River trout population this summer and have given it a clean bill of health.
Each year, fish biologists sample a couple different sections of the popular fishery between Green River Lakes and LaBarge to get a picture of the fish population and compare it to data from previous years.
The sampling technique has been used for years. Boats, equipped with generators and electrodes that dip into the water, slowly float downstream producing an electrical current that temporarily immobilizes the fish causing them to float to the surface. This allows fish biologists to catch them with a dip-net and drop them into a live well on the boat. Within minutes, the fish recover and are back to normal.
Some of the deeper holes with good hiding cover can hold a lot of fish, meaning the dip-netting can be fast and furious. The biologists don’t get them all by any means. They estimate they get about 10-15 percent during each pass, which is an adequate sample to make a population estimate. In addition to the total number of fish, the trout are all weighed and measured to get a picture of the age structure of the population and assess their general body condition. Then the data is compared to that of previous years to determine the population trend over time.
"Things, actually, looked pretty good this year," said Pinedale fish biologist, Darren Rhea. "We’re always concerned about the potential effects of extended periods of drought like we’ve had, but populations seem to be holding up pretty good in the Green."
Rhea says drought can negatively impact a trout fishery in a number of ways. "Of course you have less water during dry years, which can reduce the amount of habitat available and typically results in warmer water temperatures. This can stress the fish, making them more susceptible to disease, predation, and angling mortality." Unintended angling mortality can occur to fish from the additional stress of being caught even though it is released back into the water.
Rhea also noted that trout populations seem to be weathering a Malathion spill that occurred in the river near Daniel last summer. The spill occurred in late July of 2007 as part of a mosquito spraying project. "We definitely lost some fish to the spill, but we’re encouraged to see that our sampling efforts didn’t show a measurable reduction in fish numbers."
As you might expect, the fish managers are genuinely interested in all the fish species of the river, including those less popular with anglers such as mountain whitefish, mountain sucker, and mottled sculpin, to name a few. "We generally don’t have time to collect data on all the non-game species during these sampling efforts, but we definitely pay attention to the numbers as they are an important part of the system and a good indicator of habitat quality," said Rhea.
Managers have identified eight reaches of river to be sampled on a three-year rotation, two or three each year. This year, fish managers sampled waters above the Forest Service boundary at Kendall Bridge and downstream between 40 Rod Creek and Daniel. "Each reach is representative of a different stretch of the river and allows us to gain an understanding of the trout population throughout the entire system," says Rhea. "Some sections will show higher numbers of trout with generally smaller fish, while others are typically comprised of larger fish at lower numbers." Next year, fish managers plan to sample the river near Warren Bridge and LaBarge. "We were glad to see our estimates of fish at or above our management objectives for the reaches we sampled," said Rhea.
"Anglers should note that we recently changed the fishing regulations pertaining to the Green River to be more consistent across the entire river." Rhea added that "population estimates are an important management tool used to evaluate the status of trout populations and address the factors that affect this popular recreational fishery." For more information on the Green River or other Pinedale area fisheries, you may contact the Pinedale Game and Fish office at 1-800-452-9107 (in-state only) or 307-367-4353.
Photos by Mark Gocke, WGFD
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