Which species will survive? Climate change enhances the vulnerability of California freshwater fishes to severe drought

By Peter Moyle

As I write this on an October weekend, rain is falling steadily in Davis and has been for most of the day. This is the first real rain we have had in over seven months. But it is not the end of the drought. Multiple storms are needed. The landscape is a dry sponge, reservoirs are empty, water rationing is in place or expected to be, and aquatic species are in decline. Water agencies are trying to capture all the water they can behind dams with bypass flows for fish minimal. But what if ‘normal’ winter storms do not arrive and this record drought continues? My specific worry is for the native fishes of California, which need some of this year’s water to survive. Unfortunately, for many of these these fishes, drought is almost perpetual because dams, diversions, and other factors take or alter the water they need to survive every year.

California has a very special native fish fauna in its inland waters. Most (83%) of the 130 or so species are endemic to the state and most (80%) are in decline even without considering the effects of climate change and continuing drought. Added to this are over 40 species of non-native fishes that are irrevocably here and mostly doing well. About 10 years ago, a team at the Center for Watershed Sciences (me, Joe Kiernan, Rebecca Quiñones, and Pat Crain) developed a scoring system to predict vulnerability of fishes to climate change, especially severe drought (Moyle et al. 2013), using 20 metrics. Ten of these metrics were ‘baseline’ measures related to population size and trends, life history, and dependence on human intervention. The other ten were related to climate change such as physiological tolerances, dispersal ability, and ability to adjust to habitat change. For the climate change study, we evaluated 121 native species and 43 non-native species, and found 83% of the native species were critically or highly vulnerable to the negative effects of climate change (see graph below). Critically vulnerable species (31%) were species for which the path to extinction has already been accelerated by climate change, especially by severe drought that is a consequence of global warming. Salmon and native trout species are especially vulnerable to climate change: 22 kinds are considered to be highly vulnerable for reasons described in the report below, written by Moyle et al. (2017) for California Trout. In fact, the last fish to slide into extinction in California was the bull trout, in the 1970s.

This report and lengthier one with supporting information are available from California Trout.

Below is a list of species that in 2012 were rated as critically vulnerable to climate change. Today, I would add another 15 species to the 37 already on the list because their scores were close to the arbitrary cut-off between critically and highly vulnerable ratings in 2012 and because of drought-driven demand for the water in which they live. New species to list include northern roach, Sacramento splittail, Santa Ana speckled dace, Lost River sucker, shortnose sucker, Goose Lake redband trout, Lahontan cutthroat trout, and seven pupfish species/subspecies. The bottom line is that most native California fishes are on an extinction trajectory and their highly altered habitats are being taken over by non-native fishes. Of 124 extant species of native fishes, only 22 can be regarded as having a safe future (e.g. Tahoe sucker, Sacramento pikeminnow, coastal rainbow trout) and only three seem to fit the IUCN definition for Green-list species, once-threatened species that have recovered to occupy much of their native range as the result of human actions (Akcakaya et al. 2018, Grace et al. 2021[1]). The three ‘recovered’ species are California golden trout, Little Kern golden trout, and Modoc sucker. Long-term recovery, however, depends on continued active management.

Distribution of climate change vulnerability scores for native and non-native species in California. From Moyle et al. (2013). Highly vulnerable native fishes, top left to right, to bottom: Red Hills roach, Delta smelt, Sacramento splittail. Note that non-native species generally have low vulnerability, in contrast with native species.

We have to keep in mind that our native fishes are in decline largely because of adverse land and water use combined with invasions of non-native species. Climate change threatens long-term survival, while our current actions (or lack of them) threaten short-term survival, as delta smelt and winter-run Chinook salmon demonstrate. The most positive thing that can be said about the status of California’s native fishes is that none have become extinct in the state since the 1970s.

List of species critically vulnerable to climate change developed by Moyle et al. (2013) in 2012. Species with ++ by the name are species that appear to be somewhat less vulnerable at the present time i.e., the threat of extinction is less immediate than once thought, due to better information or positive effects of management. Species marked with # have increased their vulnerability since 2012. 

Goose Lake lamprey

Kern Brook lamprey#

Cowhead tui chub

Clear Lake hitch


Long Valley speckled dace#

Amargosa speckled dace

Owens speckled dace#

Red Hills Roach

Modoc sucker++

Klamath Largescale sucker

Razorback sucker

Longfin smelt#

Delta smelt#

Upper Klamath-Tr spring Chinook#

Sacramento winter Chinook#

Central Valley spring Chinook#

Central Valley late fall Chinook

Central Valley fall Chinook

Central Coast coho

SONCC coho#

Pink salmon[2]

Chum salmon

N Calif. coast winter steelhead

N Calif. coast summer steelhead#

Klamath Mountains summer steelhead#

Southern California steelhead

McCloud River redband trout#

Eagle Lake Rainbow trout#

Kern River Rainbow trout

California golden trout

Little Kern golden Trout

Coastal Cutthroat++

Paiute cutthroat++

Shoshone pupfish

Cottonball Marsh pupfish

Unarmored threespine stickleback

Extinctions of our endemic species can only be prevented through science-based management strategies that take both species and their habitats into account, using an ecosystem-based approach (Mount et al. 2019) that accommodates both immediate and long-term problems. There is some hope for using this developing approach, following Governor Newsome’s rapid adoption of the 30-30 policy of the UN, which has the goal of protecting biodiversity in 30% of the land and ocean by 2030. 

For this to work for fishes and other aquatic organisms in California, aquatic ecosystems managed for biodiversity must be distributed across California’s diverse landscape. Grand schemes to protect and appropriately manage biodiversity in large regions (e.g. Watson et al. 2020, Obura et al. 2021) must specifically include aquatic ecosystems. Aquatic ecosystems tend to appear as small parts of the total landscape, although they are strongly affected by what goes on in the terrestrial systems in which they are imbedded. California, with its high endemism of fishes and other aquatic/riparian organisms, should be a leader in implementing such a strategy. Conceptually, California needs a system of Freshwater Protected Areas (FPAs), akin to the Marine Protected Areas (MPAs) that have been designated along the California coast. It is clear that our current ad hoc system of Wild and Scenic Rivers, reserves, parks, and similar areas is not working well for native fishes (Grantham et al. 2017).

The starting point could be the FPA proposals developed by the Moyle lab in the 1990s, then called Aquatic Diversity Management Areas. The basis for FPAs is a classification system for inland waters of California (Moyle and Ellison 1991): all ca. 160 habitat types should be represented in FPAs. Ideally most FPAs would be watersheds that contained multiple habitat types and multiple endemic species. Moyle et al. (1996) proposed a system of 44 FPAs in the Sierra Nevada as part of the Sierra Nevada Ecosystem Project, using criteria discussed in Moyle and Randall (1998). Another 50 or so proposed FPAs are on file. Various other iterations of a grand scheme to protect aquatic biodiversity statewide have been developed, but Moyle (2002) has the most fully developed description of a proposed system of FPAs for fishes.

The three fishes most likely to become extinct next in the wild are Sacramento winter-run Chinook salmon, Delta smelt, and Long Valley speckled dace. All are on life support through artificial propagation and artificial habitats. Costs can be high and extinction still possible, even likely. Are we expecting to treat the next 50 fish species headed for extinction in the same manner?

When you lose a species, it’s forever.

Phil Pister.

[1] A formal analysis of fit to IUCN Green status has not been performed; this is an informal assessment.

[2] Pink and chum salmon are abundant north of California but reproducing populations in CA, the southern most of the species, seem to be gone.

Further reading:

Akçakaya, H.R., and 10 others. 2018. Quantifying species recovery and conservation success to develop an IUCN Green List of Species. Conservation Biology 32(5): 128-1138.

Grace, M. K. and 172 others. 2021. Testing a global standard for quantifying species recovery and assessing conservation Impact. Conservation Biology 35:1–17. https://doi.org/10.1002/cobi.13756

Grantham, T. E., and 10 others. 2017.  Missing the boat on freshwater fish conservation in California. Conservation Letters 10:77-85. https://doi.org/10.1111/conl.12249

Howard, J.K, and 12 others. 2018. A freshwater conservation blueprint for California: prioritizing watersheds for freshwater biodiversity. Freshwater Science 37(2):417-431. https://doi.org/10.1086/697996

Mount, J., and 12 others. 2019. A Path Forward for California’s Freshwater Ecosystems. San Francisco: Public Policy Institute of California. 32 pp. https://www.ppic.org/wp-content/uploads/a-path-forward-for-californias-freshwater-ecosystems.pdf

Publications to support establishment of Freshwater Protected Areas

Moyle, P. B., and J. Ellison. 1991. A conservation-oriented classification system for California’s inland waters. California Fish and Game 77:161-180.

Moyle, P. B., and R. M. Yoshiyama. 1994. Protection of aquatic biodiversity in California: A five-tiered approach. Fisheries 19:6-18.

Moyle, P. B. 1995. Conservation of native freshwater fishes in the Mediterranean type climate of California, USA: a review. Biological Conservation 72: 271-280.

Moyle, P. B., P. J. Randall, and R. M. Yoshiyama. 1996. Potential aquatic diversity management areas of the Sierra Nevada. Pages 409-478 in Sierra Nevada Ecosystem Project: Final report to Congress, Vol. III, assessments, commissioned reports, and background information. Davis: University of California, Centers for Water and Wildland Resources.

Moyle, P. B., and P. J. Randall. 1998. Evaluating the biotic integrity of watersheds in the Sierra Nevada, California. Conservation Biology 12:1318-1326.

Moyle, P. B. 2002. Inland Fishes of California. Revised and Expanded. Berkeley: University of California Press. 502 pp.

Moyle, P.B. and M. P. Marchetti. 2006. Predicting invasion success: freshwater fishes in California as a model. Bioscience 56:515

Moyle, P.B., J. D. Kiernan, P. K. Crain, and R. M. Quiñones. 2013.Climate change vulnerability of native and alien freshwater fishes of California: a systematic assessment approach. PLoS One. http://dx.plos.org/10.1371/journal.pone.0063883

Moyle, P.B., R. M. Quiñones, J.V.E. Katz, and J. Weaver. 2015. Fish Species of Special Concern in California. 3rd edition. Sacramento: California Department of Fish and Wildlife. https://www.wildlife.ca.gov/Conservation/Fishes/Special-Concern

Moyle, P., R. Lusardi, P. Samuel, and J. Katz. 2017. State of the Salmonids: Status of California’s Emblematic Fishes 2017. Center for Watershed Sciences, University of California, Davis and California Trout, San Francisco, CA. 579 pp

 Obura, D. O. and 16 others. 2021. Integrate biodiversity targets from local to global levels. Science 373 (issue 6556): 746-748.

Saunders, D.L., J. J. Meeuwig, and A.C.Vincent. 2002. Freshwater protected areas: strategies for conservation. Conservation Biology, 16(1): 30-41.

Watson, J.E., D.A. Keith, B.B. Strassburg, O. Venter, B. Williams, and E. Nicholson. 2020. Set a global target for ecosystems. Nature 578:361-362

About Andrew Rypel

Andrew L. Rypel is a Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences.
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1 Response to Which species will survive? Climate change enhances the vulnerability of California freshwater fishes to severe drought

  1. This short paper provides more outstanding work by our state’s top inland freshwater fish expert. Dr. Peter Moyle starts with the observation that “for many native fishes of California, drought is almost perpetual because dams and diversions take or alter the water they need to survive every year.” Moyle lists the aquatic species most critically vulnerable to climate change and names the three fishes most likely to become extinct in the wild. Two of them, the Sacramento winter-run Chinook salmon and Delta smelt, are no surprise to any Central Valley fish advocate. He proposes an aquatic ecosystem-based approach to saving these fish, and a strategy of identifying “a system of Freshwater Protected Areas (FPAs), akin to Marine Protected Areas (MPAs) that have been designated along the California coast.” Moyle himself has written the most fully developed description of a proposed system of FPAs in the last edition of his classic book, “Inland Fishes of California”. To help save the Sacramento winter-run Chinook salmon and Delta Smelt, fish advocates would do well to support adoption of Dr. Moyle’s proposed strategy.

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