ERIE, Pa. _ It was raining rainbows.
Recently, minutes after two tanker trucks pulled off Route 5 at the Twentymile Creek bridge, near North East, thousands of 6- to 8-inch rainbow trout literally sprayed from a stocking tube. Fish culturist Kelly McFarland held the flexible 8-inch tube at creek's edge as it jostled from the pressure of the discharged water. In a few minutes, parts of the creek were literally black with fish.
It wasn't a routine preseason trout stocking, and biologists from the state Fish and Boat Commission don't want anglers to catch these fish when the statewide trout season opens April 15.
"Hopefully, they'll be long gone into the lake by then," said Craig Lucas, manager of Fish and Boat's hatcheries at Tionesta and Fairview.
Chuck Murray, the agency's Lake Erie fisheries manager, explains:
"We grow the rainbow trout from eggs. When they come back in three years, three times as big or more, they're steelhead. We stock a million of them a year."
Rainbow trout are not indigenous to these waters, and there are no native steelhead. The fishery is totally artificial. Each fish was hatchery spawned and reared, and stocked by Fish and Boat staff or volunteers from co-op nurseries.
On this morning, about 14,000 of the fish traveled 70 miles from the Tionesta Fish Hatchery in Forest County, which raises 725,000 steelhead per year. The Fairview State Fish Hatchery in Erie County raises another 275,000, plus 20,000 brown trout yearly. Volunteers at co-op hatcheries raise more than 100,000 additional steelhead and a smaller number of brown trout.
By the end of March, Twentymile will have received about 111,000 steelhead smolt.
"At both hatcheries we've recently increased the size of the juvenile steelhead," Murray said. "Based on research that has taken place in the Great Lakes, the optimal size for release is 108 millimeters, 7.1 inches on average."
It costs more to grow 1 million small rainbows that extra inch, but Murray said it's worth it.
"The big thing is survival, and also emigration," he said. "You want them to stay (in their home waters) for a couple of weeks to imprint, but you don't want them to stay too long."
In the streams, the 7-inch adolescents fall prey to walleye and other aquatic predators; raccoons, mink and any other mammal that can catch them; and avian predators _ osprey, herons, gulls and even blue jays.
A good deal is known about imprinting, the process by which a migratory animal identifies a home to which it will return.
"It's biochemical. There are a bunch of signature chemicals specific to the individual stream. In their native environment, they're not only imprinting, they're undergoing physiological changes preparing them to go from freshwater to saltwater," Murray said. "It's a pretty powerful olfactory cue."
Sparked by temperature, photoperiod and other variables, the fish grow more silvery and are compelled to move out of the creek in a process known as "smoltification."
"Technically when they're stocked they're char," he said. "They become smolts and move out into the lake, and when they come back they've changed again and they're steelhead, which really is just a strain of rainbow trout. One is a migratory form, the other is a sedentary form."
Details of the imprinting process remain unknown. Among them is the difference in the amount of time it takes for various strains of steelhead smolt to leave the streams, and once they're sexually mature the number of days in general they will run.
Although they run in an attempt to spawn, there's virtually no successful steelhead spawning in Pennsylvania waters, where the slate or mud bottoms are not conducive to the survival of eggs.
"A number of years ago the Great Lakes Fisheries Commission secured funding to a tagging study in the upper lakes to test the differences in the behavior of various steelhead strains," Murray said. "(The study) started with lake trout, was expanded to chinook salmon and this is the first year they're doing steelhead in lakes Michigan and Huron. We're writing a proposal to bring that to Lake Erie."
Another imprinting question: Why do some running steelhead stop moving upstream when they reach the point where they were stocked as smolt? Ohio stocks the Little Manistee strain with lineage that extends to Michigan. The Pennsylvania strain is a looser collection of steelhead gathered near the mouth of Trout Run. Both states stock smolts in parts of Crooked Creek.
"It was found that near the mouth you'd find both strains," Murray said. "But farther upstream where the creek curves into Pennsylvania, they found almost exclusively the Pennsylvania strain. It's believed, but not proven, that every little feeder stream contributes chemical markers and the mature fish run until they reach those waters. They'll even go up some of these very small streams."
Murray said that although his fish are spring spawners, something that might have been acquired during the imprint process causes them to come in earlier than other strains.
"We're working on the assumption that our fish contribute more to an early run. We'd like to test that hypothesis," he said. "We think it's advantageous. When a bunch of fish show in March and April, you have a very narrow window of opportunity to catch them. Our fish don't show up in any real numbers until November."
That doesn't coincide with the window of opportunity in which anglers make the run to Erie in any real numbers.
"Every creel survey we've ever done shows we get the most angler effort in October when catch rates are still fairly low, about 2.2 fish per hour," he said. "We know the most fish are coming in in November, but we don't know why. We'd like to find that out."
