| The primary goal of this project is to understand how river flow, through its interaction with physical habitat structure, influences the survival rates of juvenile native and non-native fishes in the Colorado River in Grand Canyon. Nine research questions related to this goal have been identified in the RFP (RFP pages 27-28). These questions have a hierarchical structure and vary in scope. Some questions are fundamental and process oriented in nature (e.g., does river flow conditions alter juvenile native fish survival rates?) while others are focused on methodology (e.g., how to measure juvenile fish abundance, can small fish be marked?). Some questions, though related to the broader goals of the RFP, are quite specific (e.g., what is the Colorado River mainstem survival rate for humpback chub emigrating from the Little Colorado River (LCR) during freshets?). Some questions will be very difficult to answer within the time-frame of this project (e.g., how do biotic and abiotic factors influence individual fish growth and survival by habitat type?), or may be quite easy to answer with existing data (e.g., what is the feasibility of marking small humpback chub?).
We propose two key fundamental research questions (RQ) should guide the design of this project:
(RQ1) Do steadier flows during summer and/or fall increase survival rates of juvenile native and non-native fish?
(RQ2) To what extent does physical habitat structure (e.g., sand bars and backwaters), in conjunction with flows during these periods, influence survival rate?
We propose to address these research questions and link results to a proposed conceptual model for humpback chub Gila cypha (HBC) and other native and non-native fish (below) by first describing an approach to assess shifts in fish density by tracking habitat specific abundance and survival of native and non-native fish in response to changing nearshore habitat availability related to and created by the fall steady flow experiment. We then detail an approach to determine the source populations of juvenile native fish that populate nearshore habitats created by the proposed Fall Steady Experimental Flow (FSEF). Our intent is to link this new insight into juvenile fish ecology, with a focus on humpback chub, with the flow and habitat management capabilities of the Glen Canyon Dam (GCD) Adaptive Management Program (AMP), to create a better understanding of how flow and habitat management can be used to cultivate and enhance survival of juvenile native fish and, with time, adult native fish populations in Grand Canyon. |
