Trout Migrations and Residents Staying in Place

Brenden Kuprel’s brown trout from the Raritan River’s Island Farm Weir in March.

Natural Migrations

This was originally published in New Jersey Federated Sportsmen’s News of the New Jersey State Federation of Sportsmen’s Clubs.

Some trout travel extensively; others stay in place. What makes one fish move and another hold is an interesting question, and I’ll offer telling comparisons. They support the notion that from netfuls of hatchery fish, individuals from the batch behave quite differently. But first, I’ll write about migrations that have more to do with nature than the tendencies of recently stocked trout. Some migrations amount to native and wild trout swimming great distances, other movements limited to a watershed.

Red-spotted wild brown trout from the North Branch Raritan River at Bedminster in November. Wild browns do reproduce in Peapack Brook, which flows into the North Branch at Far Hills. Presumably, some of those browns exit the book into the river during the cool water seasons, although resident wild browns in the Bedminster region of the river may exist. Stocker rainbows have been caught in August, after all.

          Among various trout species—rainbow, brown, brook, cutthroat—some migrate. They run from rivers and streams into the ocean or the great lakes and return later to the streams they came from. In the case of rainbow trout, not necessarily will all of them exit a river for open water. Resident rainbows, at least apparently, stay behind. That might have to do with genetics turning off or on. I caught sea-run brook trout on Canada’s Gaspe Peninsula—silver fish nine inches long—from a small stream flowing into the ocean a mile below, and I never saw a brookie with normal coloration measuring that length. If more food exists in the ocean, why not?

          Other factors like environmental conditions including water temperature, water quality, and bottom makeup, can influence whether trout move or stay in place. So will a trout’s size. As I recall a story South Branch Outfitters guide Gerry Dumont told me, large tagged trout were released at Saxton Falls on the upper Musconetcong River many decades ago. Merely the matter of a contest, nothing scientific. Tags mailed in for prizes. One of the tags was returned from a fish caught in the Neshaminy Creek near Philadelphia.

Stocked trout will push upstream over low-head dams, such as this one of the South Branch Raritan at Dart’s Mill. Brookies managed to get over a low-head dam of the Shipetaukin.

Stockers on the Move

          It’s hard to imagine that any other than a large trout would make its way into the Delaware River and then swim downstream and up a tributary for a total of some 76 miles of travel. But even average-sized stockers seem to have an uncanny sense for better quality water and stream bottom—rocky rather than muddy—as the following anecdote illustrates.

          Growing up in Lawrence Township, Mercer County, I knew about three streams having to do with stocked brook trout. They were stocked by the state into Assunpink Creek, which I knew to be mud-bottomed pickerel water and the pickerel not very common. Little Shabakunk Creek is somewhat gravelly, even has some rock, but is mostly mud- and clay-bottomed, harboring suckers, bullheads, eels, and a few sunfish. As a nine- or 10-year-old, I shoveled gray clay from the side of the stream to create sculpture. Nearly the same age, I caught a couple brook trout in the creek, which I understood had made their way upstream a mile from the Assunpink.

          The most interesting movement of brook trout, however, was from Assunpink into Shipetaukin Creek, which has its confluence with the Assunpink maybe a mile further upstream than Little Shabakunk. In any case, farther than the stocking point in relation to Little Shabakunk. I had visited a chicken farm where the Shipetaukin flows through. The brother of a friend of mine worked there. Workers told me they catch trout on lunch break. I gave the creek a hard look and was not impressed, though I didn’t expect to be. It was grassy pickerel water, and I knew about the muddy bottom further upstream at Princeton Pike, a road leading from Lawrence to Princeton.

          While a senior in high school, a classmate told me he was fly fishing—and catching—brook trout upstream of Carter Road, where the Shipetaukin is one of New Jersey’s southernmost freestone streams. South of Carter Road, it’s earthen. Brook trout had traveled some three miles to live among rock and riffles much more suited to the species than sluggish flow. At least until summer heat killed them. What amazes me is that the trout swam upstream as if something in them “knew” they might find better survival conditions. Could they have scented something flowing downstream from that better water, compelling them?

      Stockers that Stay in Place   

Now for the story of a batch of fish with different intentions regarding where to hang out. What better “batch” than netfuls of trout from a stocking truck? Recently, I caught one by a Paulinksill River bridge, and a dumping spot of the North Branch Raritan, but that was only a couple of weeks after stocking took place.

          For a couple of winters, I’ve caught them almost right where they got dumped months before. A consistent few from October. The thing is, before I catch those trout, I get news about rainbows as big as five pounds caught below the confluence of the South Branch Raritan and North Branch Raritan, at Duke Island Dam. Trout that must come from the same batch but head directly downriver. The Raritan main stem isn’t stocked during the fall.

Fall stockers manage to get caught at Duke Island Dam, and even further downstream, on down below Island Farm Weir, it’s possible, perhaps.

         According to what I find on Reddit, the difference might have to do with the trout’s experience at the hatchery—tank size, feeding habits…and the amount of space explored. Another explanation I found, that it has to do with their individual instinctual responses, I think doesn’t explain much. What might explain more comes from my own reasoning after reviewing secondary sources.

         Think of a river as a holding tank. It’s possible to reshape the same amount of space in any form whatsoever, so imagine a river as a big holding tank shaped differently than so much space would take up at the hatchery. When trout get dumped, they swim around inanely, rather than taking position as well-mannered wild trout do in feeding lanes. Stocked trout seem to be doing no more than looking for pellets. Over time, they cover more and more space as they learn to eat scuds, bugs, and other food items. They spread out because they can’t find pellets, but they have senses and brains. They learn as they explore the “tank.”

          But what about the ones that stay in place? They do, because that’s easiest. Pellets don’t shower down from above, but the trout discover scuds and the like, which suits them fine. Only a relative few can, because the natural status of food sources moves most of the trout to explore more and less of the “tank.” Possibly, the relative few are the only fish that happen to find enough food without having to move for it. Those that can stay in place, probably do stay in place. Why a random few trout remain in place for months might be due to no more cause than auspicious happenstance, and the number of trout doing that is consistent year to year.

          In any event, I think the cause of movement early in the fall stocker game has to do with trout driven to find pellets. I kept trout I caught at the dump spot. Full of scuds. But not enough scuds exist there to feed 50 of them, so most of the ones not caught and taken home go elsewhere.

          I’ll finish the article with a little entertainment.

          At Carpentersville near Pohatcong Creek, a trout hatchery existed on a high bank above the Delaware River, apparently fed by large amounts of well water flow. On one occasion, the river flooded greatly, into the hatchery. Among various kinds and sizes of trout, the hatchery had big tigers. For a while, guys caught tigers as large as seven pounds upstream as the Delaware flows, below the dam on the Pequest at Belvidere. “Using bass plugs!” Dumont said.