Another program of relevance here is the Sound Ecosystem Assessment (SEA) program (funded by the Exxon Valdez Oil Spill Trustees), which is an investigation of the Prince William Sound (PWS) marine ecosystem, with a particular focus on understanding year-to-year differences in the success of pink salmon and herring. In 1994, surveys of PWS were conducted to measure plankton abundance, hydrography, currents and nutrients, with the thought being that interannual variations in these factors might lead to differing survivals of the target fish species. In addition to assessing prey abundance, studies are planned (or ongoing) to investigate the diets of the potential predator species. Related to this, the pink salmon hatcheries in PWS have begun to thermally tag the hatchery fish prior to their release. This will permit positive identification of salmon from the PWS hatcheries, and will enable better estimates of survival (from release to return) of hatchery-produced pink salmon. These survival estimates may be valid as well for native stocks, as demonstrated by recent investigations, where survival of hatchery and native pink salmon stocks from PWS showed similarly phased marine survivals, suggesting common factors (Cooney and Willette, 1996). Because of their short time in freshwater hatcheries, hatchery pink salmon are probably more representative of native stocks than would be true for other salmonids, which are hatchery-reared much longer.
The SEA study of PWS is important to future U.S. GLOBEC studies because it will improve our understanding of the sometimes complex food web of the nearshore region of the Gulf of Alaska. Depending on their relative sizes, each of the fish species (pollock, salmon, herring; see Fig. 5) is capable of preying upon all the others, including itself (cannibalism). During the productive season, say March to August, when large populations of copepods, including wintertime deep-dwelling interzonals, like Neocalanus plumchrus and N. flemingeri, develop on the shelf and in the Sound, zooplankton are a principal prey of juvenile pink salmon. The importance of immigration of these species from deep-water onto the shelf during the late spring is not known; they do not occur on the shelf during fall and early winter, so must be supplied either from deeper regions offshore, or from the deeper regions in the Sound, where they overwinter at 400-600 m depth. During the remainder of the year, the large interzonal copepods are not available to the juvenile fish; during those times other prey, perhaps euphausiids and other fishes, are the main diet. In addition to the piscivore predators, there are avian and mammalian predators on the juvenile fish of the coastal Gulf of Alaska. Figure 5 shows a schematic of a food web featuring juvenile salmon, their prey and their predators, which forms the basis of the U.S. GLOBEC program described below.
Coordination between components of PICES-GLOBEC and NOAA's FOCI program may result in better temporal and spatial coverage of important biological production processes in the Alaskan Coastal Current. FOCI has been studying biophysical variability affecting recruitment processes of the Shelikof Strait walleye pollock (Theragra chalcogramma) stock for the last ten years (Kendall et al., 1996). FOCI's studies have targeted the biophysical conditions that promote survival of pollock larvae. FOCI scientists developed a hydrodynamic model of the Western and Central Gulf of Alaska. This model could be extended to include a U.S. GLOBEC study area off PWS. Alternatively, U.S. GLOBEC scientists could develop hydrodynamic models that are compatible with the FOCI model. The FOCI program is currently focusing their research effort on the processes that determine the overall level of biological production within the Alaska Coastal Current. They are also conducting studies of the role of in situ production and transport in controlling the food supply for planktivorous fishes.