Conventional wisdom holds that stocking hatchery trout in streams that contain native trout is ecologically damaging to the native fish. Unless it's not.
In some non-prime Pennsylvania waters, hatchery-raised trout were stocked in stream sections known to contain wild (or feral) trout. In surprising research, the state Fish and Boat Commission found that years after the stocking had occurred, the native trout population had increased or remained about the same.
That data challenges the intention, if not the language, of parts of the 2010-14 Strategic Plan for Management of Trout Fisheries in Pennsylvania, which reads in part, "There are a number of streams that may hold Class A biomass trout populations that have not been officially designated as Class A streams. ... This leads to inadequate water quality protection for these waters and inconsistent application of fisheries management strategies."
Fisheries managers and commission members are faced with a conundrum. They're considering a policy change that would permit the stocking of trout on 10 sections of seven creeks, mostly in Central Pennsylvania, that are not designated as prime Class A waters (Fishing, Little Lehigh, Martins, Monocacy, Penns, Pohopoco and Yellow creeks) but include some Class A-type habitat that holds a reproducing trout population. Those streams have been stocked with hatchery trout and log high angler use on the opening day of trout season.
Waters designated as "Class A wild brook trout," "Class A mixed wild brook and brown trout" and "Class A mixed wild brook and rainbow trout" are not being considered for stocking.
Fisheries division chief Dave Miko said portions of the research support both sides of the debate. Angler interest is high.
"The literature speaks to both halves of this, and there's a lot of polarized opinion out there," Miko said. "We've done research on stocking over wild trout and what happened with those native populations. We found that when we stopped stocking over native brook trout populations and went back and sampled, the native population had increased. With stocking over wild brown trout, in about half of those [cases] the number of wild trout increased and in the other half they either decreased or stayed the same."
Miko said the sample sizes were small and inconclusive. There was no study of stocking over wild rainbows.
To many anglers, it seems counter-intuitive that native brook trout populations could increase when stocked over with bigger hatchery trout. Miko suggested it might have to do with the biological economics of put-and-take fisheries.
"Our hatchery fish aren't expected to hold over or reproduce. We generally try to stock the number of trout we think will be taken out by anglers," he said. "They're put in the system and removed so quickly. They're not necessarily vying for the same space [as natives]. They're different species with slightly different needs -- the rainbows are gullible and generally easier to catch, the browns are more difficult to catch and finicky. We think that has something to do with what our data shows."
Any impact the addition of brown or rainbow may have had on the 10 waters in question happened when the non-native species were introduced some 100 years ago, said Miko.
"We know that our current level of stocking on these 10 waters has not caused the current wild trout population to decrease," he said. "There's no connection we can make."
The Pennsylvania Council of Trout Unlimited has a wait-and-see policy.
"Our main concern is that the streams get the proper designation so we can get the water quality protected," said state council president Brian Wagner. "We're leaving it up to the Fish and Boat Commission."
An April vote on the proposal has been postponed while the agency accepts additional input from anglers through its website at www.fish.state.pa.us. The public comment period ends March 7.