Climate variations often affect the abundance, location, or migratory patterns of fish populations. Even when a fishery is entirely contained within a single jurisdiction, these climate impacts complicate the difficult task of maintaining economically efficient and biologically sound harvest management while balancing the interests of competing harvesters. When fish stocks are harvested by more than one nation, or when they cross internal jurisdictional boundaries, the management task is further complicated by the efforts of each nation or jurisdiction to promote the interests of its own harvesters.

The faltering attempts of the United States and Canada to cooperate on Pacific salmon management illustrate the fragile nature of such cooperation and the destabilizing role that climate variations can play. These two nations have a long and rocky history of alternating between cooperative salmon conservation efforts and predatory grabs at one another's returning adult salmon. The most recent breakdown in cooperation began in 1993. For 6 years, the United States and Canada were unable to agree on a full set of salmon "fishing regimes" under the terms of the Pacific Salmon Treaty. The conflict was sparked by strongly divergent trends in the abundance of northern and southern salmon stocks and a consequent change in the balance of each nation's interceptions of salmon spawned in the other nation's rivers. Alaska's salmon harvests (i.e., northern) have experienced a remarkable sustained increase over the past two decades, while harvests of some salmon stocks in British Columbia and chinook and coho harvests in Washington, Oregon and California (i.e., southern) have fared poorly. These trends appear to be influ-

Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by Thomas D. Potter and Bradley R. Colman. ISBN 0-471-21489-2 © 2003 John Wiley & Sons, Inc.

enced by the impacts of climatic variations on stock abundance, but climate is not the only source of harvest variability. Because it is not easy to disentangle natural and anthropogenic sources of variability, the negotiation process has been complicated by differences of opinion over the biological "facts."

A new agreement, signed on June 30, 1999, may end the conflict, but it is too early to judge its likelihood of success. The Canadians remain bitterly divided over the merits of the agreement, which has been labeled a "sellout" by Canadian fishing interests, and the arrangement is still contingent on U.S. Congressional approval of $140 million for two jointly managed endowment funds to be used for scientific cooperation, stock enhancement, and habitat restoration (Culbert and Beatty, 1999).

This case exemplifies many of the problems that arise in the management of transboundary fishery resources. Each nation has the power to significantly damage the other's interests and, in the short term, each could gain by interfering with the other's harvests. In the longer term, such opportunistic competition tends to squander the potential value of the fishery, as each nation commits excessive fishing capital and labor in its attempts to capture a larger share of the available fish. The ultimate result of competitive harvesting may be a "tragedy of the commons" (Hardin, 1968) in which overfished stocks are depleted and the fishery declines, sometimes abruptly.

Nations that exploit shared fishery resources often recognize the mutually destructive effects of unconstrained competitive harvesting, and they may attempt to improve the situation by negotiating harvest management agreements. The stability of such agreements hinges on the extent to which it is easy or difficult to monitor and enforce compliance and on the extent to which each party continues to expect to gain by cooperating. Many such agreements have proven to be unstable. The tendency for cooperation to degenerate into mutually destructive fish wars is a significant puzzle. The problem may have its roots in high costs of monitoring and enforcement as well as in the fact that the parties' incentives to cooperate change over time (Miller, 1996; McKelvey, 1997). Climatic variations contribute to these sources of instability by causing fluctuations in fish abundance and availability that are difficult to observe and predict. One can see the playing-out of this process in the collapse of cooperation in the Pacific Salmon Treaty case.

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