Arizona’s Mighty Chubs
In many of Arizona’s rivers and streams, the mightiest native fish predators were a group of giant minnows with the unfearsome name of chubs. These include the Gila chub, named after the Gila River, and the bonytail, humpback, round-tail, and headwater chubs. Some species grow to more than two feet long and fight hard after striking a lure. Unfortunately, these chubs have two fatal weaknesses that are seriously hampering the species’ survival.
The first is that they evolved in uncrowded ecosystems without many fish higher on the food chain, and therefore didn’t develop effective behaviors for avoiding predation. Now, invasive, exotic species like European brown trout and sunfish have been introduced to the ecosystem, and for the first time, the chubs can’t hold their own.
People love to dump buckets of live fish into new waters. Often, they are trying to create new fishing opportunities, or moving in species they’re emotionally attached to. In Arizona, one of the chubs’ worst enemies is the introduced green sunfish, a small panfish, so named because it is flat-sided and fits nicely into a frying pan. They are Midwestern natives, and when I was a boy in Michigan, I loved to fish for them because they are aggressive strikers, smashing lures that imitate small fish.
But these introduced sunfish and trout are a big threat because they are hungry for eggs and young chubs. When chubs breed, they broadcast their eggs into the water, leaving then unprotected, and then the exotics gobble them up. Green sunfish have a huge advantage — males aggressively defend their nests, ensuring that lots of young hatch, swim away, and grow up to eat more chub eggs and fry. Plus, a single female can produce up to 10,000 eggs. Where sunfish populations are established, chub reproduction often drops to zero.
The chub’s other fatal flaw is that, being fish, they need water. And there is precious little of it left in Arizona. People have drilled, pumped, irrigated, and golf-coursed our streams to death. Rivers that were navigable year-round 100 years ago, like the Santa Cruz through Tucson, are now mostly dry. Not only are the fish gone, but so are many of the streamside gallery forests that once supported the endangered willow flycatcher and other native birds. Where water remains, it is often unsuitable for chubs, which evolved in warm and fast-flowing silty rivers. Large dams like the Flaming Gorge and Glen Canyon release cold, clear water — perfect habitat for voracious introduced trout, but not for chubs.
With the lower reaches of many streams dry, the chubs that remain are in isolated headwaters, where springs fill streambeds for a distance before the water is pumped out or sinks into the ground. These remaining populations are isolated, unable to share genes or augment other dwindling populations.
The Gila chub is currently listed as endangered, and the U.S. Fish and Wildlife Service (FWS) and its partners have the daunting task of trying to save the species from extinction. There’s no way to teach chubs better parenting skills, so a crucial strategy is to kill exotics with a natural pesticide and then restock the stream systems with chubs. This expensive and labor-intensive strategy can work, but it’s a Sisyphean task because people who like to fish for green sunfish dump them into streams as fast as FWS can kill them off. One BLM fish expert tells about a day she returned to her vehicle from doing fish surveys. On the roadside by her truck she found buckets filled with boisterous sunfish. Apparently, she had scared someone off just as they were about to undertake a private restocking operation.
The U.S. Fish and Wildlife Service’s ambitious 2015 draft Gila chub recovery plan proposed “translocation,” the official name for moving fish from one place to another, to help the genetic flow (and health) between chubs isolated in headwaters. The FWS identified 17 genetically distinct strains of the Gila chub deserving long-term protection, most now found in only one or two locations in the headwaters of otherwise dry streams. To ensure survival of these strains, FWS proposed to create at least two backup populations for each one, some in artificial ponds.
Some Gila chub habitat is being restored, as at New Mexico’s Red Rock Wildlife Area, where the New Mexico Department of Game and Fish, with other groups in the Desert Fish Habitat Partnership, have secured water, restored vegetation and introduced the chubs and another endangered native fish, the Gila topminnow.
However, an important impetus for such recovery plans — the Gila chub’s endangered status — has been cast into doubt because of a taxonomic kerfuffle.
In 2015 FWS published notice that it was intending to list as threatened under the Endangered Species Act two close relatives of the already listed Gila chub — the roundtail and headwater chubs. In response, a committee of fish scientists recommended that these three species be lumped as one, which might be interpreted to mean that as a single species they don’t need listing. Other fish scientists argue that these three are indeed individual species, each deserving its own protection under the Endangered Species Act, and they have criticized the “lumpers” for basing their decision on studies that were not peer reviewed — the gold standard for scientific research. For the moment, plans to list the roundtail and headwater chubs are shelved, while the Gila remains listed as endangered pending a status review by FWS.
If FWS decides that indeed these three species are one, it could remove endangered status, arguing that collectively there are enough populations spread over a wide enough area to ensure survival. The tandem factors of climate-change-caused water loss and increasing human use of water threaten not only the chubs but other water-dependent species like the Gila topminnow, Chiricahua leopard frog, northern Mexican garter snake, and western yellow-billed cuckoo. To help tamp human’s wasting of water, Defenders and its partners oppose poorly conceived giant desert development projects, like the proposed 28,000-unit Villages at Vigneto housing development near the San Pedro Riparian National Conservation Area or the Hermosa mine — which would require 1 billion gallons of water per year — planned for the ecologically priceless Patagonia Mountains. Regardless of the ultimate listing decision, hard work lies ahead to protect chubs and other Southwestern fish, given ever-increasing demand for water by burgeoning growth in Arizona and New Mexico and water lost to global warming.
