Voices from the River: Trojan males

Brown trout are encroaching more and more on native Rio Grande cutthroat trout habitat in New Mexico.

By Toner Mitchell

The challenge of recovering native trout becomes more daunting every day.

Natives occupy mere slivers of their ancestral ranges, usually remote streams where their habitat remains relatively intact after centuries of human abuse. Many would argue that the worst of these abuses was our introduction of non-endemic rainbows, browns, brookies and cutthroats to native trout water, and that non-natives must be beaten back if native trout are to persist.

To reduce hybridization with native cutthroat, redband, gila and apache trout, New Mexico has stopped stocking rainbows in occupied or potential habitat. This has been a wise, if simple, strategy. Otherwise, recovering streams dominated by non-natives is enormously difficult, requiring the construction of migration barriers and subsequent mechanical (shocking) or chemical removals. Shocking requires repeated applications and delivers dubious results, and fish poisoning, though safe when properly executed, faces increasing public resistance.

Regardless of method, restoring natives strains stretss fish management agencies to the hilt. Restoration projects require planning, vetting, permitting and, most important, funding. Projects also consume time. Years, in fact. Years that New Mexico’s natives might not have.

The Rio Santa Barbara and Rio Chiquito, once teeming with Rio Grande cutthroats throughout their lengths, are now dominated by brown trout. The Chiquito headwaters, imperfectly protected by an elevated culvert, has about two miles left of cutthroat habitat. A couple years ago, a friend of mine caught an 18-inch Santa Barbara brown at the toe of a talus slope at 11,000 feet. These streams are but two of many five-alarm fires, highlighting the fact that non-natives are claiming territory much faster than we’re restoring it.

The recently-developed “Trojan male” technology offers a glimmer of hope in our otherwise bleak predicament. As far as I understand it, the process entails manipulating chromosomes of brood stock non-natives to the point where they can only produce male offspring with YY sex chromosomes instead of the typical XY. The extra Y chromosome is termed a “Trojan” because the males that contain it maintain their normal outward appearance. Once released into the wild, hatchery-raised Trojans will only produce male offspring, eventually resulting in an all male population that crashes due to its inability to replicate itself.

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Native Rio Grande cutthroat trout.

Like standard restoration techniques, the Trojan male approach takes years to implement. First, fisheries professionals must develop a target species brood stock. Then they must produce eggs with Trojan chromosomes, which the state of Idaho has done with brook trout. Then there must be two years of testing, including repeated Trojan stockings along with mechanical removals of wild fish to increase the proportion of Trojans to wild fish. After all that comes the waiting.

Although New Mexico has some brook trout that need disappearing, and our Game and Fish Department is testing Idaho Trojan brookies on several infected streams, what we really need is Trojan browns. Alas, it looks like we won’t have them for several years. Assuming there will still be natives by then, I often revel in fantasies of being able to catch them along dirt roads and even highways on my way home from work. Not that I’m opposed to strapping on a pack to find cutthroats in the wilderness, but given my aging physical state, I’d like the option of something much easier.

I’m well aware that I may have placed too much faith in the Trojan silver bullet. What if it doesn’t work, or doesn’t work in time? My best response is that we’d still be in our current situation, desperately bonking browns under the delusion that doing so keeps a finger in the dike. So I can live with the worst case of Trojans not working, simply because I’m living with it now.

It’s also possible that Trojan restoration will work too well, that they’ll make their way downstream and destroy all of our lunker brown trout fisheries. Part of me says, “Lord, make it so!” A much bigger part, fed by memories of gator-faced browns attacking streamers or sipping midges, would wither from grief. As much as I would love Rio Grande cutthroats to reclaim their home terrain, I would hate to think of brown trout the same way I think of steelhead, as a dream requiring a plane ticket to experience.

Basically, I’d hate to work as hard to catch browns as I do now to catch cutthroats. That said, I’ve yet to hear a solid argument against Trojan fish. In the Rio Grande’s headwater tributaries, where cutthroats are being whooped so badly by brown trout, there is a need for a technology that can extirpate non-natives at a rapid rate. In lower elevation towns and villages, farmers dewater these same streams to the point where, if it flows at all, water is too warm to sustain anything but transient trout populations. These relative dead zones are the insurance policy against Trojans making it into the Rio Grande or the Chama.

To my mind, it should be a policy we should be willing to buy. Might a Trojan or two make it through a dead zone? And if they manage to survive anglers, otters, herons, eagles, osprey, northern pike, and bigger brown trout, might these escapees reproduce? As an armchair scientist, I can definitely imagine these scenarios.

What I have difficulty imagining is Trojans persisting for the decades it would take to crash the brown trout population system-wide. Even so, it seems foolish to look to the far horizon when we’re standing on the edge of a cliff.

Toner Mitchell is Trout Unlimited's water and habitat coordinator for New Mexico. He lives and works in Santa Fe.