Everyone knows that fish need water – but just how much water is often a subject of debate, especially when it comes to fish in California’s highly managed rivers. Many studies and management decisions in the Sacramento-San Joaquin Delta and its tributaries have relied on research that found correlations between water flows and fish populations. Correlation implies a relationship between two things (e.g., when water flows in rivers are high, fish populations tend to increase). However, “correlation does not equal causation,” as the scientific saying goes: just because two factors show similar trends does not necessarily mean that one is directly causing the other. A recent report released by the Delta Independent Science Board (ISB) highlighted the need to better understand the underlying mechanisms behind the relationship between fish and flow, which can inform adaptive management of fish and water in the Delta.
The ISB was created to provide oversight of research and monitoring programs that support adaptive management of the Delta, and members are appointed by the Delta Stewardship Council. Adaptive management is a structured, but flexible, process that helps making management decisions in uncertain situations by using results from monitoring and evaluation to regularly inform the planning and implementation of a project. Before developing their recommendations for improving adaptive management in the Delta, the ISB conducted a literature review, attended relevant workshops, and interviewed 16 individuals from state and federal agencies, consulting firms, special-interest groups, and academia to understand a broad range of perspectives.
The foremost recommendation of the ISB report is to increase efforts to identify causes and effects concerning fishes and flows in the Delta at relevant time periods and spatial scales. For example, it is known that fish respond to various environmental factors differently, depending on the species, life-stage, and location. Additionally, it is generally accepted that other factors, such as temperature and salinity, interact in complex ways with flow, which complicates analyses. However, research on the fish-flow relationship to date has been species-specific, focused on just a handful of species (e.g., Delta smelt, salmonids and striped bass), and has rarely examined processes such as predation, food webs, and migration behavior that also influence fish populations. The report outlines a scientific strategy that will help develop testable predictions and better understand mechanisms underlying the effects of flow management on fish populations, and includes nine key recommendations:
1) Focus on cause and effect – the actual mechanisms that enable flows to affect fishes
2) Expand integrative science approaches across disciplines
3) Link quantitative fish models with 3D models of water flows.
4) Examine causal mechanisms on appropriate time and space scales.
5) Monitor vital rates (e.g., individual growth rates) of fishes.
6) Broaden species focus.
7) Enhance national and international connections.
8) Promote timely synthesis of research and monitoring.
9) Improve coordination among disciplines and institutions.
The ISB concludes that in order to adaptively manage the effects of flow and other drivers on fish populations and the Delta ecosystem, it is vital to understand the actual mechanisms that underlie these relationships through a more holistic and integrated framework. The ISB points out that we now have the capabilities and ecosystem understanding necessary to develop the predictive and mechanism-based models that they recommend. Furthermore, the board suggests that the Delta Science Program’s Delta Science Plan (One Delta, One Science) can facilitate the coordination necessary for this integrated approach.