GLOBEC Target Species: Interactions With Top Trophic Levels
C. T. Tynan. [NOAA NWFSC], D. Ainley [H. T. Harvey & Associates]
The proposed project addresses the need to integrate top trophic-level predators into GLOBEC interdisciplinary mesoscale and fine-scale process studies of middle trophic levels in the northern California Current system. In collaboration with physical, chemical and biological sampling within the GLOBEC-Northeast Pacific Program, our surveys will provide data to define trophic linkages between middle and upper trophic levels contributing to effects on community structure and function. Results will define top-down and bottom-up interactions, especially in regard to GLOBEC target species (juvenile salmon and euphausiids: Euphausia pacifica and Thysanoessa spinifera) which are important forage for upper trophic level predators. Information on the temporal and spatial distributions of abundant predators, and estimates of feeding rates, relative to seasonal and interannual variability in the productivity and physical forcing in the system, will be used to estimate rates of energy transfer upward from middle trophic levels. Models of trophic interactions and carbon flow within the system will greatly benefit from these data. Predation may also be a factor that explains swarming and schooling of GLOBEC target species, thus, further explaining discontinuities of zooplankton distribution. Finally, our surveys will help to focus sampling in fine-scale process-oriented studies of zooplankton by identifying foraging aggregations of seabirds and whales, which act as natural integrative plankton recorders.
From the bottom-up perspective, we propose to test the hypothesis that variation in prey density does not affect the occurrence patterns of top trophic level predators in the California Current upwelling system; or that there is no threshold of prey density that must be reached before the distribution of predators is affected. Alternately, from the top-down perspective, we hypothesize that average swarm/school characteristics, as assessed by acoustic and net sampling (i.e. size, depth, density, shape), remain the same regardless of densities and behavior of predators in the vicinity.
During 2000, we will conduct strip-transect surveys of seabirds and line-transect surveys of marine mammals in conjunction with a series of GLOBEC cruises. These cruises include mesoscale synoptic grids in May and September between Newport and Eureka extending 100 km offshore north of Cape Blanco and 150 km offshore south of Cape Blanco; and fine-scale process-oriented cruises on smaller grids (50 X 80 km). These cruises provide the temporal (seasonal) and spatial (mesoscale and fine-scale) variability in euphausiid and forage fish occurrence patterns necessary to identify the important bio-physical linkages between predator distributions and the density and availability of their prey.
During fine-scale process-oriented studies, we will collaborate with other GLOBEC researchers to examine the activities of seabirds and whales in conjunction with the horizontal and vertical structure of prey patches. Acoustic and net-tow sampling will provide the biomass, school characteristics and species composition of juvenile and adult euphausiids (Peterson, Pierce, Batchelder), juvenile salmon (Brodeur), and copepods (Optical Plankton Counter, OSU); apex predators will direct sampling toward the most dense patches of micronekton. This approach has been shown to obtain the highest zooplankton densities otherwise missed during classical gridded mesoscale surveys (Wishner et al. 1995) and to direct net-sampling, not just of commercial ventures to exploit euphausiids (Ichii 1990), but of scientific investigations on the biology of GLOBEC target species (Smith & Adams 1988).
This page was last updated on
March 15, 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