GLOBEC. TROPHIC RELATIONSHIPS OF JUVENILE SALMON IN COASTAL WATERS OFF OREGON AND CALIFORNIA: TOP-DOWN OR BOTTOM UP CONTROL?
(R.D. Brodeur, T.C. Wainwright, R.L. Emmett, W.T. Peterson [Northwest Fisheries Science Center])
We propose to study the upper-level (zooplankton, fish, birds, mammals) trophic structure and dynamics of the California Current System (CCS) pelagic zone, with a focus on the production and survival of key species such as salmonids. General effects of climate variation on biological processes in the CCS are well-documented, but few studies have focused on the processes linking physical changes with changes in the population dynamics of species in the upper trophic levels (tertiary production and above). To effectively study these linkages, empirical data and models describing the trophic structure and seasonal/interannual changes in that structure are needed.
We propose to characterize, over a 5-year period, the temporal and spatial nature of the trophic relationships within the pelagic fish community during the spring-summer transition (peak salmonid migration period) and relate these dynamics to salmonid survival. A primary focus will be identification of the strength of trophic linkages between forage and fish predator species, and the influence of these relationships on predation rates on juvenile salmon. Comparisons will be made between prey availability, diet, and food consumption for the same salmon species along a latitudinal gradient. In coastal environments, the importance of mesoscale features, such as riverine plumes, eddies, and coastal jets relative to the coastal ocean as a whole will be assessed. This will require detailed comparisons of juvenile salmon, their predators, and prey between these locations and at reference sites.
We further propose to develop a formal, empirically-based description of food-web structure in the CCS and then estimate trophic dynamics for seasons/years with adequate data. We propose to develop a multi-species population model of the CCS and apply the model in testing hypothesized linkages with lower trophic and physical processes. In particular, the model will be used to identify the relative importance of marine food-web processes (food supply, predation, competition) in controlling salmonid population dynamics, with particular focus on defining the magnitude of potential predation rates by piscine, avian, and mammalian predators. This project will interact with several existing GLOBEC projects, as well as other research projects in the CCS area.
During the first year, we plan to coordinate and take part in field sampling proposed for May and September of 2000. This will involve getting supplies ready for the collection of stomachs, parasite samples and zooplankton. Once the samples are collected, we will begin to process them and expect to have many of the May samples processed by the time of the September cruise. First year work on the modeling component will consist of describing food-web structure for the system from literature, compiling existing data on standing biomass and bioenergetics for major food web components, then incorporating this information into a trophic flux estimate. Subsequent work will refine this model on the basis of information from GLOBEC field studies, extend the flux model to a full multi-species dynamics model, and apply the model to describe the community-level changes expected from hypothesized physical-biological linkage mechanisms.
This page was last updated on
March 14, 2007.
Maintained by:
Hal Batchelder
College of Oceanic and Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064