Ohlone riffle sculpin from Sausal Creek in upper Dimond Park
For those familiar with Oakland's Sausal Creek, the rainbow trout is a beautiful and valued resident fish. Rainbow trout are regularly spotted feeding on aquatic insects in the clear, deeper pools along the stream. A lesser-known native fish that often goes undetected from the creek's banks shares the same pools and riffles as rainbow trout. This elusive fish, a freshwater sculpin, is a bottom dweller. Its intricate camouflaged mottling allows it to blend into the multi-colored cobblestones of the stream.
Recent advancements in genetic techniques have significantly improved our understanding of the diversity of freshwater sculpins in California. Sculpins (family Cottidae), which include over 42 described species in the Northern Hemisphere, can be challenging to identify, even for experienced individuals, as they are small, scaleless, mottled, and often look very similar to one another. In California, most species thrive in cool, clear streams with good water quality. Sculpins typically inhabit permanent headwaters or small isolated streams, such as Sausal Creek, which can lead to the emergence of new species due to their geographic isolation. These fish are generally abundant and play a crucial role in their ecosystems, coexisting with salmon and trout, and other native fish species. They consume a diverse range of aquatic invertebrates.
For over a century, scientists believed that the streams of San Francisco Bay were home to two species of freshwater sculpin: the riffle sculpin (Cottus gulosus) and the prickly sculpin (Cottus asper). In these streams, it is possible that only one species is present. In some cases, both species coexist but occupy different areas based on their habitat preferences, such as variations in temperature or stream reach location. We know that the sculpin in Sausal Creek are riffle sculpin because they differ morphologically (i.e., form and structure of the organism) from prickly sculpin in several key characteristics (e.g., the number of rays in the dorsal and anal fins).
Baumsteiger et al. (2012, 2014) found that morphologically similar sculpin populations in San Francisco Bay drainages are genetically distinct from inland populations. Scientists refer to species that are indistinguishable morphologically, but distinct genetically, as “cryptic” species. Moyle and Campbell (2022) analyzed the complete genome of riffle sculpin species, classifying the coastal and San Francisco Bay populations as a new cryptic species, Coastal Riffle Sculpin (C. ohlone), with two subspecies: Ohlone riffle sculpin (C. ohlone ohlone) and Pomo riffle sculpin (C. o. pomo), in honor of the native peoples who coexist with these fish. Ohlone riffle sculpin are found in streams flowing to the Central and South Bay, while Pomo riffle sculpin occupy North Bay tributaries. Sculpin found in Sausal Creek are most likely Ohlone riffle sculpin based on their geographic distribution.
The next time you spot a rainbow trout in Sausal Creek, look closely for the beautifully mottled Ohlone sculpin darting among the stream's cobbles!
–Robert Leidy, Ph.D
Further Reading:
Baumsteiger, J., Kinziger, A.P. & Aguilar, A. (2012). Life history and biogeographic diversification of an endemic western North American freshwater fish clade using a comparative species tree approach. Molecular Phylogenetics and Evolution, 65: 940–52. https://doi.org/10.1016/j.ympev.2012.08.015
Baumsteiger, J., Kinziger, A.P., Reid., S.B. & Aguilar, A. (2014). Complex phylogeography and historical hybridization between sister taxa of freshwater sculpin (Cottus). Molecular Ecology 23: 2602–2618. https://doi.org/10.1111/mec.12758
Moyle, P.B. & Campbell, M.A. (2022) Cryptic species of freshwater sculpin (Cottidae: Cottus) in California. Zootaxa, 5154 (5), 501–507. https://doi.org/10.11646/zootaxa.5154.5.1