Abstract:
In 1988-1991, the Kansas Department of wildlife and Parks stocked sauger fry in Melvern Reservoir to provide a brood source and sport fish. In 1989-1991, fall electroshocking indicated that stocking had been successful, with the 1991 survey showing three year classes of sauger. However, during spring-time electroshocking in 1992, sauger were not found; thus, this sequestered brood resource could not be utilized. To locate sauger spawning areas, I monitored movements and habitat use of adult sauger with ultrasonic telemetry, the Global Positioning System (GPS) , and a Geographic Information System (GIS) in the spring of 1993. Horizontal movements were greatest in March prior to the spawn. During the spawn, sauger exhibited high fidelity toward two reservoir shoals, where they spawned on a clay/silt, pebble, and cobble substrate. These spawning grounds were associated with a geologic district unique to one region of the reservoir. Male sauger generally occupied deeper waters than females, with both sexes inhabiting open water habitats during the pre- and post- spawn periods, and moving near shore during the spawn. After the spawn, tagged sauger were located in coves where large schools of young-of-year gizzard shad, Dorosoma cepedianum, were seen, possibly being used as prey. Barometric pressure and inflow best explained change in water depth occupied by sauger; male depths were also associated with day of year, precipitation, pool level change, and reservoir discharge, whereas female depths were further explained by water temperature. The change from expansive pre-spawn movements to minimal activity during the spawn was moderately explained by barometric pressure. It can be concluded that sauger in Melvern Reservoir responded to stimuli similar to those found in rivers during spring. Furthermore, sauger populations in such confined systems allow easily-accessed stocks for (1) sport fishing, (2) artificial propagation, (3) in situ genotype reserves for conservation of riverine populations, and (4) glochidial-host sources for threatened and endangered mussel species.
The Global Positioning System (GPS) is a superior surveying technology that quickly provides highly accurate reproducible spatial data, even in remote reference-free areas. During episodes of night-time sauger tracking, fog and darkness precluded recognition of individual coves; however, GPS coordinates of sauger found in these coves were later plotted with GIS, which proved valuable for accurate coding of reservoir regions to fish fixes, and essential in deriving data on fish movements.
Herein, I review the fundamentals, limitations, and strengths of GPS. This technology is a satellite-based navigation system that relies on radio signals having intrinsic error sources such as signal deflection, refraction, and intentional degradation by the u.s. Department of Defense. Accuracy is measured as the spatial divergence from a known location, and precision is expressed with the root mean square statistic. Either basic GPS (BGPS) or differential GPS (DGPS) can be used, depending on the spatial resolution needed and time allowed for a survey. DGPS requires more time, data processing, and personnel training, yet is more accurate than BGPS due to correction of signal errors.
