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 blog series, however, we discuss native fishes that are not considered to be in trouble, but that instead 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 fourth in the series. See our first blog in this series for an explanation of how species were chosen as examples of resiliency.
Revisit this tag to see other blogs in the Resilient California Fishes series as they are posted.
Freshwater sculpins are cryptic (i.e., having coloration or markings serving to camouflage the animal), underappreciated fishes that live in coldwater streams and lakes throughout the northern hemisphere, with 10 species in California. In California, they mainly inhabit rocky riffles, runs, and pools in cold, clear streams, where they can be quite abundant. They are rarely seen because of their small size and camouflaged coloration. Anglers catch them on occasion, when flyfishing for trout with a sinking fly, and are surprised to see a small dark slimy fish dangling from their line. Anglers in the know will put on an artificial fly called the muddler minnow, which looks (sort of) like a sculpin, to catch large trout, which may have sculpins as a regular part of their diet.
In this blog, we introduce California sculpins in general, but then focus on the Prickly Sculpin, a common species in the state, which has most of the attributes of typical sculpins except that it can live in habitats, such as reservoirs, that most sculpins cannot. Due to these characteristics, the Prickly Sculpin qualifies as a resilient California fish, while most other sculpins do not.
Sculpin basics. So, what are freshwater sculpins like? They are small (mostly less than 3-4 inches total length), bottom-dwelling fish (no swim bladder!) that sport a relatively large head with a big mouth and large pectoral fins. They are rarely seen because they have mottled color patterns that blend in well with rocky and other bottom habitats where they live. They also tend to be most active at night. When spawning time comes around in the spring, males lure females into rock cavities for spawning. The eggs are pasted onto the ‘ceiling’ of the cavities and fertilized by the male. The female then leaves care of the spawn to the male, who guards and tends the embryos until shortly after they hatch. The presence of sculpins is a good indicator of high water quality in permanent streams and lakes. They can be quite abundant and an important part of food webs in the waters they inhabit.
Sculpins typically coexist with trout, salmon, and other “‘important”’ cold-water fishes. Consequently, they have been accused of being contributors to the decline of salmonid fishes by preying on eggs and juveniles. Studies of sculpin diets do show they readily eat loose salmon eggs, as well as young salmon and trout. The supporting data comes largely from sculpins that were caught in live traps set for juvenile salmon, where the salmon were easy prey (Moyle 1977), so the data are a little suspect. Diets of free-living sculpins show that they mainly consume aquatic insects, snails, and other benthic invertebrates, eating small fish only when they are abundant and easy to ambush. Sculpins are often consumed by large predatory trout.
Sculpins are generally good indicators of high water quality and adequate flows of cool, clear water. They are also indicators of habitats that support abundant aquatic invertebrates, such as rocky riffles. Stream populations within resident species are increasingly isolated from one another, so local extinctions have no doubt occurred and will likely keep occurring, due in part to climate change.
California sculpins.The fresh waters of North America support at least 34 species of freshwater sculpin (Cottus, family Cottidae), 10 of which are found in California (Table 1). Two species, Prickly Sculpin and Coast Range Sculpin, are migratory, moving upstream from estuaries to spawn, although this life history is not mandatory for Prickly Sculpin. Remarkedly, almost all of the Cottus species look much alike, so a sculpin in a British or Japanese stream looks and behaves pretty much like a sculpin from a California stream. Most sculpin species require clear, cold water, with lots of rocky cover, to thrive. They can be quite abundant and an important part of food webs in the waters they inhabit.
Table 1. Sculpin species found in California waterways.
| Common name | Species (Cottus) | Distribution in California |
| Prickly Sculpin | C. asper | Coastal riversCentral Valley rivers |
| Coastrange Sculpin | C. aleuticus | Coastal riversN of SF Bay |
| Inland Riffle Sculpin | C. gulosus | Central Valley streams; two subspecies |
| Coastal Riffle Sculpin | C. ohlone | Santa Clara Valley, SF Bay streams; two subspecies. |
| Pit Sculpin | C. pitensus | Pit and McCloud Rivers |
| Paiute Sculpin | C. beldingii | Walker, Carson and Truckee watersheds |
| Marbled Sculpin | C. klamathensis | Klamath River |
| Bigeye Sculpin | C. macrops | Fall and Lower Pit rivers |
| Rough Sculpin | C. asperimmus | Fall and Lower Pit rivers |
| Reticulate Sculpin | C. perplexus | Widespread in Oregon and one CA stream |
In most species, the hatchlings (larvae) do not stray very far from the hatching site. Exceptions are Prickly Sculpin and Coastrange Sculpin, which have pelagic larvae that are swept downstream to rear in estuaries, rivers, or reservoirs. In a study of fishes in the Pajaro River, Jerry Smith (1982) observed that in stream reaches that dried up during a drought, Prickly Sculpin were quick to recolonize when the surface flow returned, while Riffle Sculpin recolonized more slowly. This observation of slow dispersal can be generalized to other California sculpins that have resident life histories and limited ranges (e.g., Pit Sculpin, Coastal Riffle Sculpin, Rough Sculpin). This combination makes populations of most species become isolated and therefore vulnerable to extirpation through environmental change. An interesting exception to this ‘rule’ is the Prickly Sculpin and, to some extent, the Coastrange sculpin.
Prickly Sculpin. The most common and resilient sculpin species in California is the Prickly Sculpin. Some populations behave like those of typical resident sculpins and have resident populations in cold water streams, including tail waters of large dams (e.g., Putah Creek). But they also have considerable flexibility in habitat use. For example, disposable beverage cans were documented as habitat for small Prickly Sculpin in the era before such cans were recycled (Kottcamp and Moyle 1972).
They occur in estuaries of coastal rivers because they are catadromous: adults migrate upstream to spawn in fresh water, and juveniles migrate downstream to the estuary. They are tolerant of fairly high salinities in the estuaries where they can grow to 20-25 cm (8-9 inches) in length. They are common in the San Francisco Estuary, especially in the Delta, Suisun Marsh, and the lower reaches of its inflowing streams, where temperature and salinity can be highly variable (Leidy 2007). Their tolerance of high salinity is a key reason why these fish are so widely distributed in coastal rivers; larvae can be transported by ocean currents from one estuary to another, especially during very wet years when ocean salinities may be diluted along the coast.
Most remarkably, many California reservoirs support substantial populations of Prickly Sculpin, presumably because of their pelagic larvae, even though these populations lack access to the ocean. In southern California, the sculpins in reservoirs seem to have populations that were presumably started by larvae and juveniles that were transported there via aqueducts from northern California (Swift et al.1993). Their presence in reservoirs is often overlooked because of their small size and tendency to be most active at night. We don’t know if reservoir sculpins migrate into streams to spawn or if they can spawn in reservoirs, but reservoir spawning is likely.
Prickly Sculpins’ ability to live in reservoirs may also reflect their apparent physiological tolerance of higher temperatures and salinities than most sculpin species. There is also a large and distinctive population native to Clear Lake and its outlet, Cache Creek, where summer lake temperatures can be 70-80 degrees F.
The Prickly Sculpin clearly has a high resiliency, given its wide distribution and broad spectrum of habitats in which it can live. It also seems remarkably able to persist in habitats dominated by non-native fishes. One way or another, it should be able to sustain many populations even as the climate changes. The same cannot be said about most other California sculpins, with resident (non-migratory) life histories and limited ranges (e.g., Pit Sculpin, Coastal Riffle Sculpin, Rough Sculpin). While climate change is threatening most resident species of sculpin, in part due to higher temperatures and less water, the Prickly Sculpin should continue to thrive. The persistence of sculpins can be a measure of how well we are protecting aquatic habitats in California.
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., S. A. Matern, and P. B. Moyle. 1995. Comparative ecology of prickly sculpin, Cottus asper, and coastrange sculpin, C. aleuticus, in the Eel River, California. Environmental Biology of Fishes 42: 329-343.
Kottcamp, G., and P. B. Moyle. 1972. Use of disposable beverage cans by fish in the San Joaquin Valley. Transactions of the American Fisheries Society 101: 566.
Leidy, R. A. 2007. Ecology, Assemblage Structure, Distribution and Status of Fishes in Streams Tributary to the San Francisco Estuary, California. San Francisco Estuary Institute Contribution 530.
Leidy, R. A. and P. B. Moyle. 2021. Keeping up with the status of freshwater fishes: a California (USA) perspective. Conservation Science and Practice 3(8), e474. https://doi.org/10.1111/csp2.474. 10 pages.
Moyle, P. B. 1977. In defense of sculpins. Fisheries 2(1):20-23.
Moyle, P. B. 2002. Inland Fishes of California, Revised and Expanded. University of California Press.
Moyle, P. B. and M. A. Campbell. 2022. Cryptic species of freshwater sculpin (Cottidae, Cottus) in California, USA. Zootaxa. https://doi.org/10.11646/zootaxa.5154.5.1.
Smith, J.J.(1982) Fishes of the Pajaro River System. In: Moyle, P.B. (Editor), Distribution and Ecology of Stream Fishes of the Sacramento-San Joaquin Drainage System, California.University of California Publications in Zoology 115: 83–170. https://doi.org/10.2307/1444119.
Swift, C.C., T. R. Haglund, M. Ruiz and R.N.Fisher. 1993. The Status and Distribution of the Freshwater Fishes of Southern California. Bulletin of Southern California Academy of Sciences 92 (3): 101-167.
Wydoski, R.S. and R.R. Whitney 2003. Inland Fishes of Washington, Revised and Expanded. University of Washington Press.
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