Priority, probability, and proximate cause: lessons from tort law about imposing ESA responsibility for wildlife harm on water users and other joint habitat modifiers.

• Author: Rasband, James R.

1. INTRODUCTION II. CAUSATION UNDER SECTION 9 OF THE ENDANGERED SPECIES ACT A. Section 9 and Habitat Modification as Prohibited Take B. The Regulated Community's Concerns with the Harm Regulation C. The Sweet Home Decision 1. Upholding the Harm Rule from Facial Challenge 2. Sweet Home's Guidance on Causation and Harm to Individual Animals D. Proving Causation and Individual Injury After Sweet Home 1. Historic vs. Future Injury 2. The Meaning of "Significantly Impairing Essential Behavioral Patterns" 3. Background Risk, Increased Risk, and Proof of Individual Injury 4. The Species Occupation Requirement 5. Proving Causation in Cases with Multiple Habitat Modifiers E. Causation and Prior Appropriation F. Circumventing Causation Problems by imposing Vicarious Liability III. ALLOCATING RESPONSIBILITY FOR HARM AMONG MULTIPLE HABITAT MODIFIERS A. Civil Penalties Under Section 11 B. Apportionment of Damages in Tort Cases C. Applying Tort Law Apportionment Principles to Section 11's Civil Penalty Provision D. Injunctive Relief Under Section 11 and Habitat Conservation Planning E. Applying Tort Law Apportionment Principles to Section 11's Injunctive Relief provision IV. POTENTIAL CONCERNS WITH APPLYING PRIORITY STATUS TO QUESTIONS OF CAUSATION AND APPORTIONMENT A. Fairness to Junior Appropriators B. Fifth Amendment Implications V. CAUSATION UNDER SECTION 7 VI. CONCLUSION I. INTRODUCTION

   The backbone of western water law is the basic notion of first-in-time is first-in-right. Beginning water law students have long been taught that under the law of prior appropriation, if there is not enough water in a stream to satisfy the reasonable uses of all diverters, junior users are obligated to close their head gates and pray for rain. Such occurrences have been rare because historically western states have built so much water storage (read dams) that short-term drought can be covered for even the most junior diverter. Although the assertion of priority is rare, it would be hard to imagine a more fixed principle in water law. It is increasingly evident, however, that this fixed principle of priority is being ignored when the Endangered Species Act (ESA) (1) is used to curtail diversions to assure sufficient instream flow for threatened and endangered species. Rather than impose the regulatory burden on junior appropriators, the federal wildlife agencies charged with enforcing the ESA--the Fish find Wildlife Service (FWS) within the Department of Interior and the recently renamed NOAA Fisheries, formerly and still more commonly called the National Marine Fisheries Service (NMFS), (2) within the Department of Commerce--have exercised discretion to pursue whichever appropriator they prefer. In several agency enforcement efforts, senior water rights holders have borne the brunt of obligations to provide more water. (3) Although such efforts have been relatively infrequent, in part because the ESA has not been vigorously applied to harms caused by instream flow problems, they are likely to increase. As of July 2003, some eighty-four fish species had been listed as threatened or endangered in the nineteen western states. (4)

   The purpose of this article is to raise questions in advance of this likely increase about how the ESA should be applied where instream flow deficits cause harm to threatened or endangered wildlife. (5) To that end, the article reflects upon two basic principles of tort law, namely causation and allocation of responsibility in cases of harm caused by multiple tortfeasors. Although the key Supreme Court decision on the enforcement of the ESA--Babbitt v. Sweet Home Chapter of Communities for a Greater Oregon (6) (Sweet Home)--requires the wildlife agencies to prove that a person's habitat modifying activity, such as diverting water, is the proximate cause of harm to an endangered or threatened animal, the rich body of tort scholarship, legislation, and case law on causation has largely been ignored by the agencies and the courts. Similarly, the teaching of tort law has been disregarded when it comes to deciding how responsibility for harm should be allocated among multiple habitat modifiers. By overlaying the learning of tort law on the system of prior appropriation, the legal doctrine of first-in-time is first-in-right that controls most water allocation in the states west of the hundredth meridian, this article hopes to illuminate alternative approaches to allocating responsibility for river harm that would be not only more equitable but more efficient. (7)

   A simple hypothetical illustrates some of the causation and allocation issues that arise in cases of river harm. Assume that Smith, Jones, and Williams are irrigators and the only three diverters along a hypothetical river which flows entirely within a state applying the prior appropriation doctrine. The typical total flow of the river is ten cubic-feet per second (cfs). Smith has a 1900 water right to divert four cfs, Jones a 1930 water right to divert four cfs, and Williams a 1990 water right to divert one cfs. In a drought year where the river produces only eight cfs of water, Smith and Jones continue to divert their full amounts but Williams must cease diverting.

   Assume that a particular fish, which has long dwelt in the river, has suffered marked population decline since 1990. Fisheries biologists recently determined that to spawn successfully the fish needs two cfs of water. Because in a typical year Smith, Jones and Williams divert nine of the available ten cfs, the fish has not been getting enough water. Now, suppose the Fish and Wildlife Service (FWS) wants to ensure that the fish will have the necessary two cfs per year. What happens? Should FWS be treated like just another aspiring junior appropriator? Some (most likely Smith, Jones, and Williams) might believe that FWS should be required to get a state water permit for the last one cfs of river water and then either buy or condemn another one cfs from Smith, Jones, or Williams. FWS (and the local environmental community) will likely take a different view. From their perspective, all three farmers showed up after the fish, and besides, they might add, the farmers' water rights were always subject to reasonable regulation. However firmly the farmers might hold to the view that FWS is just another appropriator, they (and surely their lawyers) know that FWS is entitled to regulate to protect the fish. While they may still retain some hope that the regulation will go "too far," and amount to a compensable taking of their water rights, they also know that such takings claims are long shots.

   But if FWS can regulate to ensure two cfs for the fish, that does not answer the question of who will have to give up the necessary one cfs of water. One approach would simply be to pin the blame on the diverter who caused the harm to the fish. As discussed below, this is in fact an element that FWS must prove under the ESA. But who was the but-for and proximate cause of the harm to the fish? Were Smith, Jones, and Williams all joint causes because but for any one of their diversions, there would be enough water for the fish? This is the wildlife agencies' current approach to causation. (8) On the other hand, did Williams cause the harm by appropriating the critical one cfs? After all, before Williams started farming, there was enough water for the fish and for Smith and Jones. To put this argument another way, does the background law of prior appropriation matter to the causation analysis? Recall that in the case of natural drought where the river produces only eight cfs, Williams would be forced to stop his diversion but Smith and Jones could continue. Should FWS's demand to leave two cfs in the river--what some have called a "regulatory drought" because the regulation rather than nature determines there is not enough water to satisfy existing uses (9)--be treated any differently than a natural drought where the last diverter on a river is the first one off it?

   If FWS can overcome the difficulties of proving causation in cases of multiple diverters with different priorities, how then should responsibility be allocated among the various diverters? Borrowing from tort law principles, one approach would be to treat Smith, Jones, and Williams as jointly and severally liable. In that case, FWS could take the fish's full needs from, say, Smith alone. This, in essence, is the approach adopted by FWS, although with a particularly inequitable twist. Whereas in tort law, when joint and several liability is imposed, a tortfeasor typically has a right of contribution, (10) under the approach to the ESA adopted by FWS, Smith can bear the entire regulatory burden without any ability to seek contribution from Jones or Williams. Thus, if joint and several liability is to be the rule of allocation, a subsidiary question arises with respect to whether there should be some right of contribution. Instead of taking any sort of joint and several liability approach, the three irrigators could also be treated as if they were proportionately and severally liable. The regulatory deed for additional water could be divided between them according to their relative contribution to the problem or on a pro rata basis. Yet a third alternative to apportionment would be to allocate with reference to priority, in which case Williams would bear the entire responsibility.

   As suggested above, the purpose of this Article is to begin considering the important but largely ignored questions raised by this hypothetical. The Article begins its inquiry in Part II by considering the vexing questions surrounding proof of causation under section 9 of the ESA which prohibits persons from taking endangered species. Specifically, it explores the meaning and subsequent application of the Supreme Court's decision in Sweet Home that to violate the take prohibition of section 9, habitat modification must proximately cause injury to an individual animal...