Comparing Futures for the Sacramento - San Joaquin Delta

6. What a Changing Delta Means for the Ecosystem and Its Fish

6 WHAT A CHANGING DELTA MEANS FOR THE ECOSYSTEM AND ITS FISH In the undisturbed state of a century ago about three-fifths of the delta was awash with an ordinary tide. Spring tides could submerge all of the backswamp. River floods were capable of overflowing the entire delta, particularly when crests, high tides, and westerly winds created a congestion above the outlet into Suisun Bay. john thompson (1957), The Settlement Geography of the Sacramento–San Joaquin Delta, California “The Delta ecosystem and a reliable water supply for California are the primary co-equal goals for a sustainable Delta.”This is the first recommendation in the long-term vision for the Delta suggested by Governor Schwarzenegger’s Blue Ribbon Task Force (Isenberg et al. 2008a). A major challenge to achieving such a balance is that ecosystem water demands are neither straightforward to gauge nor constant across or within years. Simply allocating some fixed proportion of the water for ecosystem purposes is unlikely to recover populations of desirable species,1 as evidenced by the failure of “environmental”water provisioned over the last decade or more to reverse the declines of endangered fish populations. Owen (2007) points out that a key reason for this failure is that once a minimal allocation of water is made for environmental purposes , the rest is regarded as available for diversion, making it difficult to provide additional water for unanticipated needs of fish. Moreover,evaluations of the beneficial effects of special water allocations for fish have rarely been adequate. This“managing by guessing”has a well-worn track record of failure (Ludwig et al. 1993). In the Delta, this allocation strategy has resulted in a diminishing proportion of the water being made available for fish or ecosystem needs (except since 2007, when pumping was reduced to address declining delta smelt), and poor flexibility in its use,a kind of nonadaptive management (Parma and National Center for 93 Ecological Analysis and Synthesis Working Group on Population Management 1998). In this chapter,we address whether alternatives to the present throughDelta pumping strategy can make the Delta ecosystem more hospitable to desirable fish and other organisms.2 We start by discussing the basic concepts and premises that must underlie any rebuilding of the Delta ecosystem and then assess the likely responses of key species to general export strategies. We conclude with a brief discussion of initiatives needed to make it possible to manage the Delta as a resilient ecosystem that maintains desirable characteristics, as it adjusts to natural and human-induced climatic variability. Supporting analyses and background material for this chapter are found in Moyle and Bennett (2008). BASIC PREMISES FOR REBUILDING THE DELTA ECOSYSTEM The inevitable large-scale changes described in earlier chapters will increase tidal open-water and marsh habitat area in the Delta and decrease the area devoted to agriculture and terrestrial habitat. Although the future configurations of the Delta and Suisun Marsh,3 and the rates at which they will change, cannot be predicted with detailed accuracy, both areas will provide very different habitats for fish and wildlife than they do today ,with a likely substantial increase in aquatic habitat (Moyle 2008) . Thus, plans for ecosystem “restoration” must recognize that the new ecosystem will be very different from the present one as the result of changes as fundamental as those that transformed the Delta from marsh into farmland, towns, and roads in the past 150 years. This means that there is a unique opportunity to rebuild the ecosystem into one with attributes that society decides are desirable. By recognizing that the ecosystem will undergo major change with or without human intervention, it is possible to capitalize on the opportunity to at least partially choose the characteristics of the new ecosystem and to assess how to tailor management actions to promote these choices. The indecisive alternative—letting changes such as levee failures and invasions of harmful species occur haphazardly,and hoping for the best—is unlikely to satisfy anyone. Ideally, ecosystem rebuilding will focus on creating habitat for species desired by society. However,many,perhaps most,species available to build what a chang ing de lta means 94 the new ecosystem are the alien species from all over the world already established in the Delta. Many of these alien species are regarded as undesirable , whereas most remaining native species are regarded as desirable (as indicated by the listing of many as...