Abstract
Annual precipitation inputs to the Lake Mweru basin, Zambia, were computed from historic data and recent gridded data sets to determine historic (1925–2013) changes in lake level and their potential impacts on the important fisheries of the lake. The results highlight a period from the early 1940s to the mid-1960s when interannual variability of inputs doubled. Existing lake level data did not capture this period but they did indicate that levels were positively correlated with precipitation one to three years previously, reflecting the hydrologic storage of the lake, the inflowing Luapula River and the upstream Bangweulu wetland complex. Lag cross-correlations of rainfall to El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole were weak and spatially and temporally discontinuous. The two drivers were generally positively correlated and induced opposing effects upon annual precipitation and lagged lake levels. This correlation became non-significant during the time of high observed interannual variability and basin inputs were prone to the vagaries of either driver independently or reinforcing drought/excess conditions. During times of high flows and persistent elevated lake levels, breeding habitat for fish increased markedly, as did nutrition supplied from the upstream wetlands. High hydrologic storage ensures that lake levels change slowly, despite contemporary precipitation totals. Therefore, good conditions for the growth of fish populations persisted for several years and populations boomed. Statistical models of biological populations indicated that such temporally autocorrelated conditions, combined with abundant habitat and nutrition can lead the “boom and bust” of fish populations witnessed historically in Lake Mweru.
Highlights
The diversity and abundance of species available in the allotropic fishery of Lake Mweru are significant to local, national and international markets [1,2,3]
All tests were performed at the 0.05 level notion of increased interannual variability during this period
Despite the minimum annual requirement of 30 operating stations, the varying numbers and locations of stations used to estimate basin input were a weakness, as was the change in the estimated mean level of input corresponding to the extension of the record after 1986
Summary
The diversity and abundance of species available in the allotropic fishery of Lake Mweru are significant to local, national and international markets [1,2,3]. The serially autocorrelated nature of lake inputs resulting from precipitation and the large upstream Bangweulu wetland complex have profound effects on the delivery of nutrients and the availability of habits in the lake. Such temporal (hydrologic and nutrient inputs) and spatial (habitats) correlations are key factors [4] producing apparent erratic ecosystem behavior or “surprises” [5], with marked interannual variations in fish stocks. The Mweru basin lies on the margin of influences from the Atlantic and Indian Oceans [9], juxtaposed to the East African Highlands and Rift Valley, and beneath the climate over the region [9]. The Mweru basin lies on the margin of influences from the Atlantic and annual passage thejuxtaposed
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