By Peter B. Moyle
We are living in the Anthropocene, an era being defined by global mass extinctions caused by humanity. While on-going and impending extinctions of birds and other terrestrial vertebrates gain the most attention, the situation with freshwater fishes (and other freshwater organisms) is as bad or worse, partly because many freshwater extinctions are nearly invisible events, hidden by murky waters (Moyle and Leidy 2023). The extinction threat is especially high for obligatory freshwater fishes including many species endemic to California (Moyle and Leidy 2023). The ultimate cause is competition between people and fish for clean water. People are winning the competition at an accelerated rate, assisted by invasive species and global warming and by the by continued expansion of the human population and its demands (Rypel 2023). The freshwater fish fauna of California is thus already on its way to becoming simplified and homogenized (Moyle and Mount 2007, Leidy and Moyle 2021).
The challenge, then, is how do we save some of the evolutionary lineages of native fishes to become the post-disaster ancestors of future fishes in the near (50-100 years) and long-term (100-1,000+ years)? This essay presents a rough proposal for answering this question. It is based on the assumption that it is desirable to save some evolutionary lineages of California’s native fishes to serve as ancestors of future fish species, for moral, aesthetic, and practical reasons. But volumes have been written about these reasons for saving ‘worthless’ species (see, for example, Marchetti and Moyle 2010, Rypel et al. 2021) so they, so they don’t need to be reiterated here. Suffice to say, the more fish species that are lost, the poorer the world’s freshwater ecosystems will be, as will the people that also depend on them today and in the future.
The Earth has undergone mass extinctions in the past. The best known is the asteroid-driven extinction at the end of the Cretaceous period, which may have coincided in part with massive volcanic eruptions. Interest in these events stems in part because they are regarded as the cause of extinction of the dinosaurs, allowing mammals, our ancestors, to dominate the world’s megafauna. Not much thought has been given to freshwater fishes that survived this disaster, even though streams in much of the world would likely have run high and muddy for hundreds if not thousands of years, until the stabilizing influence of trees and other terrestrial vegetation was renewed. Thus, the ancestors of most abundant and diverse group of freshwater fishes today, the Ostariophysi (carps, catfishes, characins) presumably survived the Cretaceous extinctions because of pre-adaptations for living in the murky waters flowing through a devastated landscape.
Mass extinctions have been caused by people in the past as well. The idea that people wiped out the megafauna of the lands they invaded as they moved from their ancestral home in Africa across the globe is now widely accepted. For example, Flannery (1994, 2015) described humanity’s ancestors as ‘Future Eaters’ because their consumption to extinction of large native mammals and birds resulted in major cascading changes to every ecosystem. This extinction seriously altered the native flora and fauna. In a way, modern extinctions are just a continuation of this human impact.
Now we are faced with increased frequency of disasters affecting humans and ecosystems resulting from, or exacerbated by, global warming. This reality has gripped the attention of many people, including scientists, politicians, and policy makers. But denial of global warming and its effects remains common, and despite climate disasters growing larger, more frequent, and more diverse. Millions of refugees worldwide are already seeking to survive outside their homelands, as their home areas become unlivable and/or dangerous due to droughts, floods, wars, disease, and a host of other problems. Such disasters are tragic symptoms of the declining planetary suitability of habitat for people, due in part, to population pressure exacerbated by global warming. This loss of habitat for people bodes poorly for fishes, especially those that require fresh water.
Characteristics of future ancestors
So, what freshwater fishes in California are likely to be good future ancestor material? What fishes can survive under the more likely and more pessimistic (realistic?) scenarios of a future in which most native freshwater fishes have been eliminated or close to it. Below are some examples, good and bad, of future ancestors. I assume here that large-scale moving of fishes of native fishes to new water bodies is neither practical nor desirable. I base the answer to the question on quantitative studies of characteristics of successful invasive fishes (Moyle and Marchetti 2006) and on vulnerability of California freshwater fishes to global warming (Moyle et al. 2013).
Ostariophysi. The Superorder Ostariophysi has major lineages worldwide in fresh water including carps, minnows (cyprinoids), catfishes, and characins. The fish of this superorder are usually among the most abundant fishes where found, with 11000+ species. They apparently were a minor part of the freshwater fauna at the time of the Cretaceous extinction event but survived to become dominant. There are many reasons for this but among them are likely a keen sense of hearing (Weberian ossicles), wide range of adult sizes, high fecundity, omnivory, high mobility, and high tolerance of poor water quality. These are all characters that would allow small populations to survive in devastated landscapes and to colonize new or recovering areas rapidly. So fishes such as common carp, various minnows, and catfishes could be likely ancestors for future freshwater fishes, worldwide. In California, sucker species (Catostomidae) and diverse cyprinoid fishes (Leuciscidae), such as Sacramento pikeminnow, hitch, chubs (Gila, Siphatales), and roach (Hesperoleucus) have the ostariophysan characteristics which may increase survival chances of at least some of the species.
Speckled Daces. The speckled daces are a lineage of ostariophysan native fishes (genus Rhinichthys) that seem ideally suited to become future ancestors. They were, until recently, regarded as one species, living in diverse habitats from British Columbia to Southern California and Mexico. In fact, “speckled dace” represents 15-20 isolated lineages (species and subspecies). Moyle et al. (2023) showed there are seven such lineages in California alone. They are remarkable because while genomics indicated that species-level populations have been separated for a million years or so, the separate populations are recognizably “speckled dace”; individuals from divergent populations cannot be readily told apart by people. Clearly the basic features of dace morphology and behavior are very conservative genetically and remained consistent over the 6+ million year history of this fish group. To achieve this broad distribution and diversity, these fish had to survive and thrive during long periods of changing conditions and dynamic geologic events, including periods of extreme drought and flood during the Pleistocene. Features that contribute to the survival all dace species, besides the basic ostariophysan characteristics, include (a) broad physiological tolerance, (b) small body size so large populations can continue in small waters, (c) flexible habitat requirements, and (d) ability to quickly colonize new or recovered waters. But even speckled dace may have a hard time persisting in isolated environments that are highly altered (e.g., Santa Ana speckled dace in the Los Angeles region).
Unlikely future ancestors. Some of today’s fishes, have a poor chance of being ancestors of future California fishes, if present trends continue. Many of these fishes are migratory species important in fisheries that that require large habitats (i.e., rivers, large lakes, estuaries) with relatively cold water (maximums <20° C for critical life stages). California fishes that qualify are sturgeons, all species of salmon and smelt, and most species currently listed as threatened or endangered under ESAs.
White and green sturgeon are fishes whose ancestors survived the Cretaceous extinction event(s) but presumably in ways opposite those of the Ostariophysans, by being large and highly mobile and by living for 100 years or more, with high fecundity. They also had a refuge in ocean waters. But both species are in danger of extinction in California, from multiple causes, as shown by the recent die-off in the San Francisco Estuary (Schreier et al. 2022). This reflects their increasing inability to live in human-dominated ecosystems. Their large size is no longer an advantage, unless northern rivers become more habitable for them.
Coho and Chinook salmon now depend on hatcheries for their survival in California; their future therefore is not secure. This is true for salmon in general at the southern end of their ranges; they are unlikely to make it to 2100 without human assistance (Lackey et al. 2006, Franks and Lackey 2015). Without a major change in human behavior, the future of salmon, at least as wild populations, is in Canada, Alaska, and Siberia (Rypel and Moyle 2023).
Endangered species. ESA-listed species already require intense care by people to persist, such as reproduction in hatcheries. Pupfishes, Colorado pikeminnow, and other desert fishes will survive without continual human assistance only if water is provided for them during extreme droughts, which is unlikely given water supply stresses in desert areas. Each listed species has its own challenges; the difficulty in overcoming these challenges is generally why they are listed and mostly not recovering. The challenges are only becoming harder to overcome.
Caveat. A problem I have largely ignored in this essay is that some of the most likely future ancestors in California waters are non-native fishes. Many are abundant and widespread, and have displaced native fishes. So they have already passed a suitability test of sorts, an ability to thrive in new, highly altered environments and an ability to become widely dispersed in their new homes, assisted by people. To make matters worse, invasive non-native fishes are often on the forefront as drivers of extinctions, a one-two punch with global warming (Moyle 2020, 2021). Examples of likely ancestors of future California fishes include Mississippi silverside, common carp, western mosquitofish, largemouth bass, and tilapia species.
People have had short but highly damaging impacts on most of this planet’s inhabitants, and the immediate future looks to be one in which effective collective action seems unlikely. We can therefore expect the current global extinction event to only accelerate; fishes will disappear as fast or faster than terrestrial vertebrates. The event will be recorded geologically as having taking place in the blink of an eye. But some animals and plants will survive. These will be the future ancestors. How can we maximize the pool of future ancestors in California, under the supposition that the more lineages that survive, the more diverse future lineages will be available to adapt to the changed world? This would seem to be desirable if more people choose to become a benign part of the Earth’s ecosystems and that diverse fishes are part of those ecosystems. While unlikely, in California, a start in this direction would be to establish Freshwater Protected Areas under the state’s 30×30 Initiative. See also Moyle 2002, Moyle et al. 2020, Rypel 2023.
Establishing a system of Freshwater Protected Areas now, as part of the 30×30 Initiative, would be a major step for aquatic conservation in California. Such a system should encompass California freshwater fish fauna, and other endemic aquatic biota. There will be tendency, of course, to give habitat for ESA-listed species a priority. But many of these species are or will become conservation dependent, requiring interventions of various sorts (e.g. hatcheries) even if habitat is provided (e.g., delta smelt). They have a low probability of surviving under most likely scenarios described previously. A preponderance of native fishes already are listed under ESAs or considered to be in decline (species of special concern). These fishes have an increasingly high probability of going extinct as long habitat alteration continues and severe droughts alternate with extreme floods, driven by global warming and human unwillingness to make sacrifices necessary to reverse global warming.
The best chance for listed species is probably to be part of clusters of species that have high potential for future ancestor-hood. These species would have to be managed as a unit within their natural habitat. In the Sacramento River watershed the ancestor species, all unlisted, could include: tule perch, prickly sculpin, hardhead, speckled dace, California roach, Sacramento sucker, Sacramento pikeminnow, and rainbow trout. The ideal place to conserve these fish could be undammed streams and their watersheds, such as Deer, Mill and Antelope creeks in Tehama County or the Fall River in Shasta County. In the Klamath region, special status and protection of habitat could be given to the combined Shasta, Scott, and Salmon rivers, as well as the connecting Klamath River in the region. Other possibilities include Goose Lake and its watershed, the Eel River and its watershed, the San Gabriel River and adjoining watersheds in Southern California, and the Owens-Death Valley region including Owens Lake.
While moving fish to other watersheds (assisted migration) is usually not a good idea, the Eel River is an intriguing example of where it seems to be working because the Eel now supports populations of Sacramento pikeminnow, coastal roach, and Klamath speckled dace, introduced from adjacent watersheds. However, the negative effects of these ‘native’ introduce d species on Eel River native fishes, especially salmonids, and invertebrates may outweigh the positive effects of establishing new populations. But the three species do have an increased probability of becoming future ancestors as a result.
The initial steps for future ancestor conservation would be to improve the habitat where needed and make selected watersheds as disaster-proof as possible. This could be done, for example, by intense forest and fire management, by reducing road impacts, by improving floodable areas (e.g., bypasses and wetlands) and by generally creating a system that provides habitats that can persist though decades of droughts and floods. Ideally, there would be monitoring and management by local people who are committed to protecting the watershed and its biota.
Essentially, the idea is to treat Freshwater Protected Areas as habitat for future ancestors much as you would critical habitat for ESA-listed species, only for multiple species. However, if the global climate disaster becomes as severe as some speculate, refuges for future ancestors should be able to persist on their own, with little or no human management, for a long time: decades, perhaps hundreds of years.
If you think the idea selecting and protecting future ancestors is laughable, think of what the world will be like in the next 50-100 years if present trends continue, including increasing temperatures. If changes in climate are denied, then it seems silly to deny related changes in ecosystems that are affected by global warming. Currently, most sacrifices needed to reduce the impact of global warming are being rejected, ignored, or minimized. The oceans will be much warmer, so coral reefs and other marine ecosystems will likely be reduced or eliminated, as will most oceanic fisheries. Warmer oceans will be tied to floods and droughts at a world scale, with larger storms, challenging infrastructure such as levees and dams. More people will become climate refugees, with fewer safe places to go. In such scenarios, future ancestors of any creature but humans will receive little consideration. Species will survive to become ancestors mostly by chance, being lucky enough to survive in an unplanned refuge or being capable of surviving in a devastated landscape (cockroaches, rats, and maybe mosquitofish). But perhaps we can increase chances of survival for diverse lineages, including fishes, by creating some refuges now, as a gift to the future.
I hope this vision of the future is overly pessimistic and that California’s leadership in combating global warming, protecting natural areas, and saving endangered fishes (and other species) will continue. We need to keep working to protect California’s amazing natural heritage on the assumption that the global community will come to its senses and take the actions needed to halt, then reverse global warming.
Peter B. Moyle is a Distinguished Professor Emeritus at the University of California, Davis and is Associate Director of the Center for Watershed Sciences.
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 Alternate labels are climate change, global harming, or global disaster creation. Global warming is preferred because it is the driver of other disasters lumped under the innocuous “climate change.”