A STUDY ON FISH NEST ABUNDANCE IN THE KIGOMA REGION OF THE EAST AFRICAN RIFT LAKE TANGANYIKA: A POSSIBLE PROXY FOR RECENT ENVIRONMENTAL CHANGE

East African Rift Lake Tanganyika is one of the oldest, deepest lakes in the world and is rich in biodiversity with over 1,400 species. One particular species of cichlid fish creates nests in the sandy substrates of the lake. We completed a census of fish nests in the Kigoma region of Lake Tanganyika (Tanzania), indicating the density of nests varies along similar water depths. The study site is characterized by a low gradient, open shoreline with deforested bluffs to the north and the Luichi River delta to the south. Sonar images of the substrate capture the fish nests as small circular depressions. The occurrences of fish nests were counted over equal areas of the sonar records in equal water depth (~10 m) along a 12 km, shore-parallel transect. Three equal areas at each site were counted and averaged to obtain fish nest density per site. Individual counts of cichlid shell nests varied between sites, ranging from 3 to 57. Site 11 (5.54 km from delta) contains the most nests, averaging 50 fish nests. Site 1 (12.07 km from the delta) averages 6 fish nests per area, the fewest recorded. At the south end of the field area, the number of fish nests decreases with increasing distance from the delta (R^{2 =}0.6496). The variation of fish nests and its inverse correlation with distance from the delta suggests that the nest abundance is not negatively affected by delta sedimentation; rather, the low nest density within the northern field sites may reflect increased sedimentation from the adjacent deforested hill slopes.