Foodbase Resources
The aquatic protocol evaluation panel had concerns with the lack of empirically established linkages between food base and fishes (Bradford et al., 2001), and identified that a possible consequence of the recent increase in primary and secondary production may differentially benefit non-native species (competitors or predators) over native species. Because of this, additional research and the restructuring of the existing foodbase monitoring program is warranted in light of its importance toward meeting stakeholder objectives. For this reason, a refocusing of the monitoring and research efforts is to be undertaken toward assessing whether primary production is actually limiting the abundance and structure of the downstream fish community directly or indirectly through abiotic and biotic interactions.
A series of integrated studies will address a number of issues identified by the aquatic protocol evaluation panel (Bradford et al., 2001). Primary focus is on the research and development of an organic budget and foodweb linkage program as an organizational framework to determine whether or not the aquatic foodbase is limiting, and to determine what organic sources, and where limitations occur within the Colorado River system. This requires multiple approaches: 1) continuation of phyto-benthic and invertebrate monitoring, with some modifications from what has been done in the past, focused initially in the Lees Ferry section; conduct in-stream metabolism and community respiration experiments; 3) quantify organic and inorganic carbon supply and fluxes (decomposition, transformations and residency); 4) based on findings of the organic mass balance research design and effective sampling program having the appropriate sampling locations, methods and frequency for assessing and quantifying organic flux (sources, pools, transformations and movement), and 5) develop a better understanding of foodweb linkages within the spatial distribution of the entire fish community.
In Lees Ferry the food base derived from primary production is considered an important biotic resource because of its direct linkage to higher trophic levels, potential limitations (density dependence), use and availability required to support the waterfowl and rainbow trout fishery. Algae/macrophytes and invertebrates consisting mostly of midge larvae (chironomids), and amphipods (Gammarus) form the major components of the aquatic food base in Lees Ferry. The conventional phyto-benthic and invertebrate monitoring will be continued in this upstream section. The frequency of these sampling efforts will be intensified to monitor effects due to experimental fluctuating flows and beach habitat building flows. Additionally, a new method for measuring community metabolism and respiration will be assessed to determine its feasibility for estimating primary production in Lees Ferry. Contingent on study outcome, community metabolism may be more effective and serve as a surrogate to conventional indexes used for evaluating primary production.
Several research projects assessing food-fish linkages have been recently implemented. These include: bioenergetics modeling (Peterson, 2003) and diet and predation associated with non-native trout removal project at the LCR (Coggins and Yard, 2003). Following the aquatic protocol evaluation panel recommendations, it is proposed that an organic mass balance project be used as an indicator of system-wide production and export. A request for proposals will be developed during 2004 for this initiative.