Resilient California Fishes: Sacramento Pikeminnow

By Peter B. Moyle and Thomas L. Taylor

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The fresh waters of California support a diverse, highly endemic fish fauna. Many of them are on extinction trajectories. In this “Resilient California Fishes” blog series, we discuss native species that have sufficient resiliency to keep populations large and sustainable, even in highly altered habitats. Information on these species should help us to understand why they have such resiliency in the face of large-scale changes to California waterways. This blog is the third in the series that started with an account of the Sacramento Sucker (Moyle and Taylor 2025). Revisit this tag to see further blogs in the series as they are posted.

Introduction. The Sacramento Pikeminnow is a much maligned native fish species, accused of suppressing populations of Chinook Salmon and other important (to humans) fishes in the rivers of northern California. About forty-five years ago it invaded the Eel River basin, where its predatory behavior is accused of frustrating habitat restoration attempts to recover depleted runs of Coho Salmon, Chinook Salmon, and Steelhead. Are these accusations justified? Here is a short summary of our responses to that question.

Distribution. Sacramento Pikeminnow are abundant and widely distributed throughout the Sacramento and San Joaquin River systems in low-elevation waterways. They are native to several coastal stream systems as well, such as the Russian and Salinas Rivers. They are also found in major foothill rivers upstream of the rim dams and in many of the smaller streams on the Valley floor, including medium-sized urban streams. They have been introduced (illegally) to the Eel River and some southern California streams (see below). This wide distribution in a variety of habitats indicates their adaptability, so they need to be managed accordingly. Most streams in their native habitats are cool enough that they support salmon and trout as well, at least in the larger rivers.

Figure 1. Close-up of a juvenile Pikeminnow showing the pointed mouth and somewhat flattened head. The photograph was taken in the San Joaquin River at the Willow Creek confluence, where a large mixed school of juvenile Pikeminnow and Hardhead were hanging out. August 1996. Photo by Tom Taylor.

Pikeminnow as predators. Sacramento Pikeminnow can grow to a large size (adults can be 2-3 feet long). It is a predatory “minnow” that lacks teeth in its jaws and has a large, pointed mouth contained in a somewhat flattened head. Dagger-like pharyngeal teeth are located in the throat, at the back of the head, and efficiently masticate any consumed prey. The common name reflects a body and head shape that are somewhat similar to ‘true’ pikes of the eastern USA (family Esocidae). The ‘true’ pikes have mouths lined with sharp teeth in the jaws. Juvenile pikeminnow are opportunistic predators that feed on small fish and crayfish, as well as on aquatic insects and other invertebrates when small. In streams, adult pikeminnow typically hang out in deep pools during the day but move into shallow water at night to forage. Their prey is mostly fish and crayfish, including out-migrating salmon. Naïve hatchery-raised Chinook Salmon are especially vulnerable to their predation because they lack the survival skills of wild juvenile salmon. Hatchery-reared juveniles may be released in large pulses of small confused fish. Of course, pikeminnow are just one of a number of predators, many of them non-native, that also forage on juvenile salmon (Grossman 2016; Stompe et al. 2020). Predator control programs have been suggested as a way to increase survival rates of endangered salmon and other fishes that are prey for Pikeminnows, and these programs have been deployed in other states. But there is little evidence that a predator control program would decrease Pikeminnow predation in their native habitats (O’Rear et al. 2018). In central California, the Pikeminnow is a native fish species adapted to surviving severe droughts, floods, and other natural disasters and to preying on other native fishes (Moyle 2002).

Taxonomy. Four species of pikeminnow are endemic to western river systems. The Sacramento Pikeminnow (Ptychocheilus grandis) is still abundant in much of its native range. It has been successfully (and illegally) introduced into the Eel River in Northern California and into streams in Southern California (Moyle 2005), and some of those introductions have occurred via water transfers from California’s Central Valley. The Colorado Pikeminnow (P. lucius) is an endangered species that has been extirpated from the lower Colorado River in California but still persists upstream in other states. The Northern Pikeminnow (P. oregonensis) is widespread in the Columbia River watershed and is often regarded as a problem species because juvenile salmon can be a high percentage of the adult diet at times. The Umpqua Pikeminnow is endemic to just one Oregon river but has been introduced into the Rogue River. The common name for Pikeminnow was changed from Squawfish by the American Fisheries Society Names of Fishes Committee because of the negative connotation that name had for Native American women.

Pikeminnow in the Eel River. The adaptation of Pikeminnows to California’s rivers and climate is seen in their successful invasion of the Eel River, the third largest watershed in California, where Pikeminnow are not native. The river has a flow regime similar to other coastal watersheds: long dry summers and rainy winters and springs. At some time in the late 1970s, Pikeminnows were introduced into Pillsbury Reservoir on the Eel River, presumably by anglers using small silvery juveniles from the Russian River as bait. Their population expanded rapidly, and they quickly spread to accessible habitats throughout the Eel River basin (Brown and Moyle 1997). A few decades earlier, Coastal Roach (Hesperoleucus venustus), another California endemic species, was introduced into the Eel from the Russian River and quickly spread throughout the Eel watershed as well. It is likely that the rapid spread of the Sacramento Pikeminnow was facilitated by the abundance of Roach in the river, which served as familiar prey.

Adult pikeminnow under the water. The water is blue green. There is a sandy bottom. — Figure 2. Adult pikeminnow keep their distance from a snorkeler in a large pool in the Merced River along Highway 140 in the Merced River Canyon downstream of Yosemite National Park. This river is undammed upstream of this reach and so retains excellent habitat quality including large deep pools with lots of cover. August 2006. Photo by Tom Taylor.

Pikeminnow in the Sacramento River. In the Sacramento River and tributaries, ‘pike’ show their abundance when thousands aggregate for spawning in the river and large seasonal tributaries. As described in O’Rear et al (2018), CDFW, for a number of years, permitted a fishing derby to kill Sacramento Pikeminnow below Red Bluff Diversion Dam, where Pikeminnow congregated on their way upstream to spawn, before climbing fish ladders at the dam. Hundreds were caught and killed, but there was no evidence that it made much difference to out-migrating juvenile Chinook Salmon numbers. It is probable that predation on salmon by Pikeminnow was increased by the existence of the diversion dam. Juvenile salmon were migrating downstream when Pikeminnow were migrating upstream. To get past the dam, the juvenile salmon (mostly of hatchery origin) had to pass through spillways, mainly at night. The turbulence below the spillway disoriented juvenile salmon, which then became easy prey for Pikeminnow. In essence, the dam structure created places where large Pikeminnow could hold in place and ambush the disoriented juvenile salmon trying to emigrate to the ocean. This predation was enhanced when lights on the dam were turned on. Presumably, the dam delayed the upstream spawning migration of Pikeminnow, increasing encounters with juvenile salmon. The dam was decommissioned in 2013 and is no longer an obstacle to both salmon and pikeminnow. Regardless, the predator control efforts did not appear to benefit the salmon.

In contrast, the Northern Pikeminnow in the Columbia River have been shown to impact salmon populations through predation on juvenile salmon on their way out to sea. An intense research program documented that the problem was real, and this resulted in a unique Northern Pikeminnow control program where anglers got paid a bounty ($6-10 per fish) for catching and killing pikeminnows over nine inches long. The bounty program has significantly reduced pikeminnow predation on salmon and made some anglers very happy to be paid for fishing (see http://www.pikeminnow.org).

Sunlight catches a small school of yearling pikeminnow swimming over a bedrock shelf. There are speckles of light and bubbles under the water. — Figure 3. Sunlight catches a small school of yearling pikeminnow swimming over a bedrock shelf in the North Fork Yuba River near Convict Bar. The pattern on the bedrock was created by cases of an aquatic moth in the family Pyralidae. The incredible regularity in their distance from one another is a mystery but is one of the amazing things you can discover snorkeling California’s foothill rivers. August 2021. Photo by Tom Taylor.

In Central Valley tributaries, such as Deer Creek, North Fork American River, and the Merced River, schools of large Pikeminnow are usually associated with pools that have complex cover elements (e.g., rock crevices, fallen trees); large pools without much cover usually don’t harbor Pikeminnow. Where the stream habitat is suitable for pikeminnows, the different life history stages occupy different habitats. This is due in part because adult Pikeminnows will prey on juveniles, so the juveniles are often living in shallow riffle or edge habitat. Juveniles typically feed on a wide array of small aquatic invertebrates, while large adults (over 25 cm long) prey mostly on crayfish, other fish, and amphibians. However, pikeminnows are highly opportunistic in their diets. Novel prey (e.g., lamprey larvae, water shrews) will be taken when available (Moyle 2002). Adults seem to feed mainly at night, moving out of their home pools and into fast water to forage (Harvey and Nakamoto 2006). When biologists like us wade in gravelly riffles, it is not unusual for juvenile pikeminnows to follow close behind, feeding on invertebrates stirred up by the waders.

A juvenile pikeminnow under water with lots of bubbles at the top of the image and rocks with algae at the bottom. The fish are in the middle. — *Figure 4. Juvenile pikeminnow actively feeding at the head of a pool in the North Fork American River about a half mile upstream of the Iowa Hill Road crossing. July 2014*. Photo by Tom Taylor.

Conclusions. The Sacramento Pikeminnow is obviously a very resilient species. But does it deserve its reputation as a predator that limits salmon populations? Yes, if only the Eel River population is considered. In the Sacramento River, Stompe et al (2020) found that non-native adult Striped Bass had a diet very similar to that of adult Pikeminnow, concluding that any attempt to control one species likely would result in an increase in the other species. In the historic range of Sacramento Pikeminnow, there is increased appreciation of its role in river ecosystems, as an opportunistic predator, with Chinook Salmon as just one of its natural prey species. Its large size and waryness also make Sacramento Pikeminnow a challenge for anglers to catch, but an easy fish to view by snorkeling through its pools. We do not advise consuming Pikeminnow caught by angling because, as a top predator with a fairly long life span, they accumulate heavy metals (like mercury) and pesticides in their flesh. Also, like any minnow, the flesh contains many bones.

About the Authors

Peter Moyle is Distinguished Professor Emeritus at the University of California, Davis and is Associate Director of the Center for Watershed Sciences.

Tom Taylor has had a long career as an agency and consulting biologist, often working with native fishes. He has also taken underwater photos of many of the fishes, which will illustrate the blogs.

Further Reading

Brown, L.R. 1990. Age, growth, feeding, and behavior of Sacramento Squawfish (Ptychocheilus grandis) in Bear Creek, Colusa Co., California. Southwestern Naturalist 35; 249-260. https://doi.org/10.2307/3671937

Brown, L. R., and P. B. Moyle. 1981. The impact of squawfish on salmonid populations: a review. North American Journal of Fisheries Management 1:104-111.

Brown L.R., and A.M. Brasher, 1995. Effect of predation by Sacramento squawfish (Ptychocheilus grandis) on habitat choice of California roach (Lavinia symmetricus) and rainbow trout (Oncorhynchus mykiss) in artificial streams. Canadian Journal of Fisheries and Aquatic Sciences 52:1639–1646. https://doi.org/10.1139/f95-758

Brown, L. R., and P. B. Moyle. 1997. Invading species in the Eel River, California: successes, failures, and relationships with resident species. Environmental Biology of Fishes 49: 271-291.

Gard M. F. 2005. Ontogenetic microhabitat shifts in Sacramento pikeminnow, Ptychocheilus grandis: reducing intraspecific predation. Aquatic Ecology 39(2):229-35.

Grossman, G.D. 2016. Predation on fishes of the Sacramento-Sacramento Delta: Current Knowledge and Future Directions. San Francisco Estuary and Watershed Science 2020;18(1).

Harvey, B.C. and Nakamoto, R.J. 1999. Diel and seasonal movements by adult Sacramento pikeminnow (Ptychocheilus grandis) in the Eel River, northwestern California. Ecology of Freshwater Fish 8(4): 209-215.

Kinziger A.P., R.J. Nakamoto, and B.C. Harvey. 2014. Local-scale invasion pathways and small founder numbers in introduced Sacramento pikeminnow (Ptychocheilus grandis). Conservation Genetics 15(1):1-9.

Moyle, P. B. 2002. Inland Fishes of California, Revised and Expanded. Berkeley. University of California Press.

Nobriga M.L., F. Feyrer, and R.D. Baxter, R.D. 2006. Aspects of Sacramento pikeminnow biology in nearshore habitats of the Sacramento–San Joaquin Delta, California. Western North American Naturalist 66(1):106-14.

O’Rear, T.A. J. R. Durand, and P. B. Moyle. 2018. Killing Native Fishes for Fun and Predator Control. California WaterBlog https://californiawaterhblog.com/2018/08/05/killing-native-fishes-for-fun-and-predator-control/

Stompe D.K., J.D. Roberts, C.A. Estrada, D.M. Keller, A. Balfour, and A.I. Banet. 2020. Sacramento River predator diet analysis: a comparative study. San Francisco Estuary and Watershed Science 18(1) 16 pp.

Vondracek, B., Baltz, D.M., Brown, L.R., and Moyle, P.B. 1989. Spatial, seasonal and diel distribution of fishes in a California reservoir dominated by native fishes. Fisheries Research, 7(1-2) 31-53.