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Physical Characteristics of the Environment influencing Pelagic FishesProgress Reports (PDF): FY 2000, FY 1999, FY 1998, FY 1997, FY 1996, FY 1995, FY 1994
Physical characteristics of upper waters of the Hawaiian EEZ will be characterized through use of satellite-tracked drifters, and from satellite measurements other ocean features (e.g., surface temperature and topography, pigment concentration, wind stress). This information will provide an environmental framework that should complement related studies of the Pacific Pelagic Fisheries Program by enabling a more comprehensive interpretation of fishery data relevant to management.
The physical environment can influence the distribution of fishes in at least two different ways. Water movement can move fish from one place to another. Alternatively, the water temperature, oxygen content, proximity to land, and other factors may either attract fish or cause them to move away. Understanding of both influences is necessary to define fish habitat and to forecast the abundance and distribution of fish stocks.
Instruments that drift with movement of the surface layer of water, measure the properties of the water, and report their positions by satellite will be deployed in the Hawaiian EEZ. The design of these drifters and arrangements for their deployment have been completed. The first drifters were deployed from the Townsend Cromwell in August 1994 and are currently transmitting date to the University.
The historical database of ARGOS-tracked drifters has been used to study mesoscale processes in the lee of the Hawaiian Islands. Although the number of drifters is too small to construct instantaneous maps of the flow, the average velocity field reveals a pair of elliptical counter- rotating gyres west of the islands, the cyclonic one to the north of 20\170N, the anticyclonic one to the south, The major axis of the gyres extend from approximately 157\170W to 161\170W.
It is hypothesized that these large gyres are the average expression of individual cyclonic and anticyclonic eddies induced by wind shear lines in the lee of the islands, which eventually drift westward and decay. To confirm this hypothesis, the Central Pacific Drifter Array, consisting of seventy drifting buoys, will be deployed over the next two years to map the flow in the Hawaiian Exclusive Economic Zone. The first batch of 25 drifters was deployed in September 1995 south of the island of Maui; these drifters have been entrained in a large anticyclonic eddy, approximately coincident with the mean gyre. About 25% of the drifters continued westward in the North Equatorial Current, whereas the remaining ones drifted northward and became entrapped in an intense mesoscale eddy field located over the western Hawaiian Islands.
The current positions of these drifters are sent to interested people by fax.
Funding was received at the University in August 1993.