By Peter B. Moyle and Tom L. Taylor

This is the second blog in a series on native California fishes that seem to be doing well despite multiple threats. They are still common and widely distributed, despite major changes to their habitats. The Tule Perch (Hysterocarpaus traskii) is an interesting species to include in this series because it contains three distinct subspecies, two of which seem to be doing well and one that is not. The first, Sacramento Tule Perch (H. t. traskii), has lost some habitat in the Sacramento River system (e.g., San Joaquin River on the Valley floor) but is still common in the main rivers below dams and has also colonized “new” habitats where they can be abundant (e.g., hydropower reservoirs). The second, Russian River Tule Perch (H. t. pomo), is widespread and abundant in the river and may have benefited from water projects that increased summer flows (Cook et al. 2010). The third, Clear Lake subspecies (H.t. lagunae), appears to be scarce in the lake, in contrast to the 1970s when we sampled the lake and found Tule Perch to be fairly common. 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.

Introduction. Tule Perch are attractive little fish (adults less than 20 cm long) that are endemic to Northern California. They are the only freshwater fish species in the surfperch family (Embiotocidae). This family is made up of 22 marine species plus Tule Perch, mostly from north Pacific Coast habitats. The surfperches gained attention as early as the Gold Rush era because they are viviparous (live-bearing), an unusual trait in spiny-rayed fishes. In 1854, they became the very first freshwater fish species formally described from California, by a physician, beating out several other species described in the same newspaper in the same year (Evermann and Clark 1931). Tule Perch bodies are thin and almond-shaped, with a small, hard mouth adapted to picking or sucking up small invertebrates and then crushing them with flattened pharyngeal plates in the throat. The perch comes in a variety of color patterns: white or yellow bellies and barring on the sides that are narrow, wide, or even absent. 

Distribution and Taxonomy. Tule Perch are widespread in central California, with three distinct geographically-defined populations: Russian River, Clear Lake, and Sacramento River and tributaries. These three populations are isolated from one another and are regarded as separate subspecies, with distinct life histories (Hopkirk 1973, Baltz and Loudenslager 1984). The Russian River Tule Perch is abundant and widespread in a coastal river that has historically had wide fluctuations in flow, which, when very low, greatly limited habitat. The year-to-year uncertainty of river habitat caused the perch to develop a life history to deal with this variability. The fluctuations led to high mortality rates in many years, so the fish evolved to be mature at a small size and reproduce at higher levels. Thus, females have high fecundity, giving birth to 12-45 tiny young in their first year of life. They rarely live more than two years. It is likely that Russian River Tule Perch have benefited from the construction of two large dams, which release water into the river in summer, reducing variability in flows (Cook et al. 2010). 

In contrast, Clear Lake and Sacramento Tule Perch live three to eight years and do not start breeding until their second year. Each female produces 25-60 young, the number increasing with size and age. Sacramento Tule Perch occur in a wide variety of habitats, including turbid sloughs of the Delta and Suisun Marsh, the main Sacramento River and tributaries, and Britton Reservoir on the Pit River (Moyle 2002).

Tule Perch are small, deep-bodied, spiny-rayed fish that are viviparous (live-bearing), with females giving birth to 10-60 young each year. The number and size are related to the mother’s body size, age, and habitat. They favor cool water habitats in low gradient reaches of rivers where there are deep pools that have rock walls or boulders and/or complex vegetative cover. The cover consists of branches that have fallen from riparian trees, as well as cover created by riparian vegetation that hangs into or over the water, or from floating aquatic vegetation. The key here is that such habitats need to provide complex cover for pregnant females and newborn young. The young are precocious, so they swim away as soon as they are born, mostly in May or June. The males grow fast and mate with females by September. Females also grow rapidly and store sperm from mating with multiple males until used for fertilizing the eggs, usually in January. This unusual trait presumably evolved to protect them from predators, allowing the perch to thrive in diverse habitats, including estuaries, seasonal rivers, lakes, and reservoirs. They are generally found in habitats that have high water quality, featuring cool, clear water in rivers and lakes. However, they are also found in turbid water, such as is found in Suisun Marsh and other parts of the Sacramento-San Joaquin Delta. 

Diet. Tule Perch feed on abundant benthic invertebrates and zooplankton. It was surprising to us to watch the perch foraging in flowing waters, because their deep bodies would seem to make it difficult for them to hold in place to forage on the bottom and other substrates. However, they are in the surfperch family, and marine species of that family often occupy turbulent habitats in the surf zone. These fish propel themselves with the use of their pectoral fins and use their small caudal fin for steering. The pectoral fins are used to effectively row themselves through the current. In Suisun March and the Delta, they mainly feed on abundant amphipods (Corophium), both native and non- native species. In Clear Lake, they feed mainly on zooplankton and aquatic larvae of midges and gnats. The diet is similar in the Russian River, where they feed on a variety of aquatic insects found in or on the benthos and on aquatic plants. Basically, Tule Perch eat whatever small aquatic invertebrates are abundant in their habitats. The presence of Tule Perch bones in middens of Indigenous people indicates they were consumed at times, despite their small size. 

Resiliency. The different life history patterns of Tule Perch has allowed them to live in altered habitats that also support non-native fishes. Their deep bodies, spiny fins, viviparity, and use of complex cover presumably discourage predators. The ultimate test of their resiliency was the attempt by CDFG in the 1950s to poison, with rotenone, all fish in 460 km of the Russian River and tributaries to favor steelhead. It was assumed that the diverse community of fishes in the river was somehow suppressing the steelhead population. The poisoning was a failure, although thousands of fish were killed, including Tule Perch and other native fishes. The Tule Perch population recovered in just a few years (Cook et al. 2010).

Conclusions. Tule Perch favor cool water habitats in low gradient reaches of the rivers where there are deep pools with lots of vegetative structure in the water, and they also occupy areas with boulders and underwater rock faces. Juveniles may be found in connected ponds on the floodplain in wetter years. They can also live in turbid waters associated with the Sacramento-San Joaquin Delta and in lakes and reservoirs. While the perch have overcome many human-caused changes to their habitats, there is no reason to be complacent about their long-term persistence; climate change will make the waters they inhabit warmer, smaller, and more variable, especially in Clear Lake. The resilience of Tule Perch will be severely tested in the coming years, so monitoring populations of the three subspecies should be formalized. The Tule Perch is a remarkable species, unique to California, so it deserves attention. 

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

Baltz, D. M., and P. B. Moyle, 1981. Morphometric analysis of tule perch (Hysterocarpus traski) populations in three isolated drainages. Copeia 1981: 305-311.

Cook, D.G., S. D. Chase, and D.J. Manning. 2010. Distribution and ecology of the Russian Tule River Tule Perch. California Fish and Game 96(2):146-164.

Baltz, D. M., and P. B. Moyle. 1982. Life history characteristics of tule perch (Hysterocarpus traski) populations in contrasting environments. Environmental Biology of Fishes 7: 229-242 

Gobalet, K. W., P. D. Schulz, T. A. Wake, S. N. Siefkin, 2004. Archaeological perspectives on Native American fisheries of California, with emphasis on steelhead and salmon, Transactions of the American Fisheries Society 133: 801–833. https://doi.org/10.1577/T02-084.1

Hopkirk, J. D. 1973. Endemism in Fishes of the Clear Lake Region of Central California. University of California Publications in Zoology 96:1-160.

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

Pintler, H. E., and W. C. Johnson. 1958. Chemical control of rough fish in the Russian River Drainage, California. California Fish and Game 44(2) 91-124.

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