Glen Canyon Dam Adaptive Management Program Administrative History

ABSTRACT: The Colorado River below Glen Canyon Dam, Arizona, is part of an adaptive management programme which optimizes dam operations to improve various resources in the downstream ecosystem within Grand Canyon. Understanding how populations of federally endangered humpback chub Gila cypha respond to these dam operations is a high priority. Here, we test hypotheses concerning temporal variation in juvenile humpback chub apparent survival rates and abundance by comparing estimates between hydropeaking and steady discharge regimes over a 3-year period (July 2009–July 2012). The most supported model ignored flow type (steady vs hydropeaking) and estimated a declining trend in daily apparent survival rate across years (99.90%, 99.79% and 99.67% for 2009, 2010 and 2011, respectively). Corresponding abundance of juvenile humpback chub increased temporally; open population model estimates ranged from 615 to 2802 individuals/km, and closed model estimates ranged from 94 to 1515 individuals/km. These changes in apparent survival and abundance may reflect broader trends, or simply represent inter-annual variation. Important findings include (i) juvenile humpback chub are currently surviving and recruiting in the mainstem Colorado River with increasing abundance; (ii) apparent survival does not benefit from steady fall discharges from Glen Canyon Dam; and (iii) direct assessment of demographic parameters for juvenile endangered fish are possible and can rapidly inform management actions in regulated rivers.

Even unmanaged ecosystems are characterized by combinations of stability and instability and by unexpected shifts in behavior from both internal and external causes. That is even more true of ecosystems managed for the production of food or fiber. Data are sparse, knowledge of processes limited, and the act of management changes the system being managed. Surprise and change is inevitable. Here we review methods to develop, screen, and evaluate alternatives in a process where management itself becomes partner with the science by designing probes that produce updated understanding as well as eco- nomic product.

Renewable natural resources provide important contributions to food, fiber, and recreation in many parts of the world. The economies of some regions a r e heavily dependent on fisheries and forestry, and consumptive use of wildlife (hunting) is a traditional recreational pastime across Europe and North America. The management of renewable resources usually involves public agencies that are responsible for harvest regulation, and often production enhancement, so as to provide sustainable yields into the long-term future (resource husbandry). The track record of such agencies has been spotty: many resources have been mined to low levels before effective harvest regulation could be developed, while others have been managed so conservatively as to miss major harvesting opportunities.

Three key features of renewable resources have made them difficult to manage. First, sustainable production depends on leaving behind a "capital" stock after each harvesting, and there are definite limits to the production rates that this stock can maintain. Second, harvesting is normally undertaken by a community or industry of harvesters whose activities (investment, searching, etc.) are not completely monitored or regulated, so that dynamic responses, such as overcapitalization of fishing fleets, are common. Third, the biological relationships between managed stock size and production rates arises through a complex interplay between the organisms and their surrounding ecosystem; for any particular population, this relationship cannot be predicted in advance from ecological principles and must, instead, be learned through actual management experience.

This book is on the various methods of environmental impact assessment as a guide to design of new environmental development and management projects. This approach surveys the features of the environment likely to be affected by the developments under consideration, analyses the information collected, tries to predict the impact of these developments and lays down guidelines or rules for their management.

This book is concerned with practical problems, e.g. development in Canada, the management of fisheries, pest control, etc. It is devoted to a general understanding of environmental systems through methods that have worked in the real world with its many uncertainties. It does not reject the concept of environmental impact analysis but rather stresses the need for fundamental understanding of the structure and dynamics of ecosystems.