Taxa occurrence (presence/absence) and composition of benthic macroinvertebrates from trawl surveys (2003-2017) conducted on Lake Victoria, Uganda

A Ponar grab (with open jaw area, 238cm2) was used to take sediment samples for analysis of benthic macroinvertebrates. Three spread hauls were taken from each sampling point. The bottom type at each point was described from the grabbed contents. Each of the three samples (hauls) from each area was then concentrated placed in labeled sample bottles, and preserved with 5% formalin solution and taken for laboratory analysis. In the laboratory, each sample was rinsed with water to remove the formalin and then placed on a white flat-bottomed tray. Using pair of forceps all macro-invertebrates were sorted from the sediment and the individual taxa identified to the lowest possible taxonomic level using identification manuals and a dissecting binocular microscope at 4 x 25 magnification. All taxa from the different hauls were recorded and individuals of each taxon enumerated to estimate their densities from which the following results were generated. The taxa were identified using taxonomic keys by Mandahl-Barth (1954), Pennak (1953), and Merritt and Cummins (1997). De Moor et al. (2003).

The datasets present data for trawl surveys conducted between 2003 and 2017. However, not all transects or years may be represented in the sample as depending on resources, sampling may not take place in some years or transects.

The samples were immediately processed in the field and treated with formalin to keep the organisms of interest intact and prevent them from rotting. To avoid loss of organisms during sample processing, appropriate mesh sizes were used.