The San Francisco Bay ecosystem will experience a wave of extinctions – unless we take action soon
Scientists describe the global and accelerating loss of species from human action in recent times as the Earth’s sixth extinction event, akin to earlier die-offs from asteroid strikes and massive volcanic eruptions. It is, unfortunately, becoming common to hear about extinctions in far off places like the tropical rainforests or coral reefs. But unless we take action quickly, 2015 will be the year that a wave of extinction begins in the San Francisco Bay-Delta estuary.
San Francisco Bay and its vast watershed form an estuary that supports a diverse array of native aquatic plant and animal species. Chinook salmon, sturgeon, smelt, steelhead and other native fishes depend on the annual pulse of freshwater flow from our rivers into the estuary to complete their life cycles. One hundred and fifty years of altering the estuary by reducing natural flows and destroying wetland and floodplain habitats have devastated these species; the recent drought has only made a bad situation worse.
That’s why it is so distressing that the State of California decided to suspend the water quality standards for freshwater flow to San Francisco Bay in February and March, and is likely to do the same in April and May. Those standards, required by the state and federal Clean Water Acts, are designed to share water between the environment and human uses in wet years and dry; in very dry years like this one, the amount of freshwater that is required to reach the Bay is already very low. Still, even these reduced flows are a lifeline for many species. Suspending the rules when many of our native fishes are listed as endangered and/or their populations are at record or near record lows, is likely to lead to extinction for one or more of our native species, and other permanent changes to the Bay ecosystem.
For example, Delta smelt (which exist nowhere else on Earth) reached its all-time record low last fall. California’s Department of Fish and Wildlife tows a big net behind a boat in Delta smelt habitat hundreds of times every fall in order to measure the population; historically, that method caught hundreds of Delta smelt between September and December – last year eight (8) of these fish were caught. A different survey, conducted earlier this month, found only six Delta smelt. When one of the estuary’s most common fish disappears, the ecosystem that supported it is obviously in big trouble – as are all the other species that are linked to it (as prey and predators) in the estuary’s rich and complex food web.
Populations of our iconic Chinook salmon and steelhead are in free fall as well. Not too long ago, the endangered winter-run Chinook salmon was beginning to recover from decades of decline, with returns topping 15,000 fish. But last year, only 3,000 of these fish returned from the ocean – and, as a result of bad water management decisions in 2014, 95% of their offspring have already been lost.
It’s not just the species that are listed as endangered that are in peril. Starry flounder, which rely on the estuary as a nursery, are at the second lowest level on record;
so are Sacramento Splittail, a unique minnow species that is food for everything from our native sturgeon to the wading birds that live along the estuary’s shoreline.
An overwhelming amount of research shows that as freshwater flows from our rivers to the Bay increase, so do populations of each of these species. Fish need water – you don’t need to be a scientist to know that – and one of the best documented facts about the estuary is that the health of its unique wildlife and habitats is linked to the amount and timing of water that actually reaches San Francisco Bay during the winter and spring.
Reducing natural flows also means the estuary is more susceptible to invasion by non-native species. According to a recent study by three distinguished ecologists, “(a)ltered flow regimes by human activities can [alter] the ecological impact of drought … and increase the susceptibility of ecosystems to invasion.”1
Figure 3: Comparison of estimated unimpaired flow from the Central Valley to the San Francisco Bay (runoff that would reach the estuary if there were no human storage or diversion upstream) with actual flows to San Francisco Bay. Even under normal conditions, less than half of the Central Valley flow makes it to San Francisco Bay — during a drought, people store and divert an even higher proportion of the freshwater needed by fish and wildlife.
Now the State Water Board is taking away even the pittance of freshwater flow the estuary is entitled to under existing standards, and the state and federal agencies that are charged with protecting fish and wildlife are looking the other way.
If the State Water Board’s decision to suspend required levels of freshwater flow continues through March and is extended into April and May, no one can say exactly which of our species will go extinct or exactly when. But there is no doubt that cutting off the lifeblood of the estuary is pushing species closer to extinction than ever before and is causing permanent alteration of this ecosystem. The drought is bad enough; robbing the estuary of ecologically critical flows, when its species are hanging by a thread during the fourth year of a drought – that’s just asking for a wave of extinctions to commence.
What you can do: Let the State Water Resources Control Board and other agencies know that suspending Bay inflows in March and through the spring could mean extinction for some of our native species. Ask them to:
- Reverse the decision to suspend the D-1641 March requirements for inflows to San Francisco Bay and ensure that these flows critical to the continued existence of Delta smelt, winter-run Chinook salmon and other species are actually provided for the rest of March and on through the ecologically important spring period.
- Reverse its decision to partly suspend the D-1641 limits on export pumping, in order to prevent devastating impacts on the last remaining Delta smelt and winter-run salmon.
- Reject any new petitions to suspend the flow requirements and export limits for April and May 2015, and give the endangered species of the Bay-Delta estuary their last, best chance for survival.
 Winder, M. , A. Jassby, and R. MacNally. 2011. Synergies between climate anomalies and hydrological modifications facilitate estuarine biotic invasions. Ecology Letters 14:749-757