PORTERSVILLE -- Lurking among acres of bottom-hugging hydrilla, Lake Arthur muskellunge approaching 50 inches lie in wait to ambush any prey that passes.
And at Pymatuning Reservoir, a record number of walleye congregate near dozens of submerged habitat improvements.
Results from April trapnet surveys conducted by the state Fish and Boat Commission suggest that fish management strategies have paid off at two of western Pennsylvania's most popular lakes.
Tim Wilson, a fisheries biologist for the state Fish and Boat Commission, said anglers willing to adapt to changing conditions at Lake Arthur and Pymatuning could see better results.
"Like everything, lakes change," he said. "Sometimes anglers will figure out a strategy that works for them and they'll stick with it for years. But these lakes have changed over the years and it's necessary to adapt to those changes."
At 3,225-acre Lake Arthur, Butler County, the survey was part of an ongoing trapnet study to evaluate the impacts of 2007 changes to muskellunge size and creel limits. In subsequent years muskie anglers complained about declining catches, and in 2011 Fish and Boat documented the absence of entire year classes of muskies, fish ranging from 26 to 32 inches.
At the time, Wilson deduced the muskie problem was the result of habitat changes and a cyclical population trend. Encroachment of the invasive hydrilla verticillata weed, which grows in dense mats, had displaced the previously dominant Eurasian watermilfoil that commonly grew in tangled floating beds, providing great cover for fish. Spikes in Lake Arthur's muskie population in 2004 and 2007, he said, could have resulted in massive cannibalization of some 3,300 young muskies averaging 6 inches stocked those years by PFBC. That, coupled with other predation, could have resulted in the loss of muskie year classes noticed by anglers. Wilson recommended doubling the stockings.
This year's trapnet capture and release of 39 muskellunge was down a bit from 2013 (53 captured) and about equal to 2011 (41 captured), indicating relative stability in the lake's muskie population. Wilson said anglers who have learned to fish the new hydrilla habitat are doing better than those still trolling past the remaining milfoil.
"There's no lack of vegetation in Lake Arthur," said Wilson. "A lot of bays still have the classic milfoil beds, lily and coontail, but hydrilla is still very prevalent. And it's still a very good muskie lake. Anglers weren't wrong about the decline in number of muskies, but they were comparing [2011 populations] to the very best it's ever been, which was an abnormal period. What we have now [a trapnet catch rate of 0.054 per hour] is very proportional."
Additional trapnet captures show Lake Arthur is fast becoming a catfish haven, locating 559 channel cats up to 29 inches, and 34 brown bullheads.
Last month the nationwide nonprofit Recreational Boating and Fishing Foundation rated Moraine State Park, which includes Lake Arthur, the 15th best family fishing location in the United States. The criteria included "public water containing plenty of common game species." The trapnet survey logged 524 bluegills, 92 black crappies and 44 white crappies, as well as hybrid striped bass and yellow perch.
Walleye numbers were up significantly at Lake Arthur. The survey found 66 walleye as large as 28 inches. Wilson said many more could have been missed -- weather delays forced the survey to be held after the walleye spawn.
"A few degrees of water temperature that impacted fish movement could have had an effect," he said.
Sixty miles north at Pymatuning, which straddles the Ohio-Pennsylvania line in Crawford County, the trapnets were set primarily for walleye. The long cold winter helped researchers, who were able to survey Pennsylvania's best walleye fishery at the height of spawning. What they found surprised them.
From 2001 to 2007, said Wilson, Pymatuning walleye fishing was "really lousy" despite robust stocking by Ohio and Pennsylvania wildlife agencies. In 2008, after several consecutive years of very low trapnet catch rates and gripes from anglers, biologists stopped stocking fry (three to four days old, 1/3 to 1/2 inch) and switched to fingerlings (35 to 40 days old, 1 to 1 1/4 inches). The larger fish were significantly more expensive to raise, but the survival rate was higher.
Those year classes have now come of age. The 2014 trapnet capture rates, said Wilson, were "exceptional."
"The population of legal walleye in Pymatuning is better than ever," he wrote in the report. "Very large year classes that started as fingerlings stocked in 2009, 2010 and 2011 have reached legal length [15 inches] and now comprise the vast majority of the walleye population in Pymatuning Reservoir."
The trapnet catch spiked from fewer than 1.5 fish per hour in 2013 to five fish per hour this year. The nets collected 4,585 walleye -- 3,900 measuring 15 to 20 inches. More than 1,000 were in the 17-inch range; 92 percent were 15 inches or larger.
Wilson said the impoundment is particularly conducive to the needs of walleye.
"It's just a really good combination of habitat, the shape of the lake basin, water quality and size. It's a 14,000-acre lake. Just the sheer size has a huge effect on walleye," he said.
Pymatuning Reservoir is jointly regulated and managed by both states, which have in recent years teamed up on habitat improvements designed to concentrate walleye and other fish at points recognized by anglers.
Last week, a partnership including Ohio Department of Natural Resources, Ohio State Parks, the Pymatuning Lake Association, Pennsylvania Fish and Boat, the state Department of Conservation and Natural Resources and volunteers sank more than 150 wooden cribs in 8 feet on the lake's north end, and rock reefs in 6 feet in the south.
"All of the state agencies are determined to make fishing better on Pymatuning," said DNR fisheries biologist Matt Wolfe, in a written statement. "The goal of this project is to introduce structures into the waters of northeastern Ohio in order to recruit the next generation of anglers and retain the anglers who already enjoy the sport of fishing."
Additional captures found a good number of muskellunge, 37 in the 25- to 48-inch range. But a third of the fish showed signs of current or past infection from the often-fatal redspot disease (epizootic ulcerative syndrome).
The survey logged 1,366 yellow perch as large as 13 inches, more than 500 catfish (bullheads and channel cats up to 28 inches), 582 black crappies as large as 15 inches and 471 bluegills. The capture included 700 common carp -- famous for being fed in masses by wildlife watchers at Linesville.
Substantial numbers of baitfish were found, including more than 2,200 alewifes and nearly 700 golden and spottail shiners. And while some nearby lakes have been overwhelmed by gizzard shad, the Pymatuning trapnet survey turned up only 61.