Abundance and composition of fish in sites with varying degradation levels in Lake Wamala

Study Extent

The study was conducted between October 2016 and October 2017 in sites with different levels of land degradation. Papyrus was the common vegetation adjacent to water and the different sites of the lake are surrounded by different thicknesses of this vegetation although, in some sites, it has been cleared up to the lake’s shoreline. Seven sampling sites were selected for the study. The sites were categorized into three as follows: (1) Less degraded sites (2) Degraded sites, and (3) Riverine sites, based on the level of adjacent land degradation, the thickness of the shoreline vegetation and location near the river mouth.

Sampling

The sites for data collection were chosen depending on the adjacent land cover or land use within the lake riparian buffers. Three sites (Lusarila, Kilaza, and Bagwe) were adjacent to the degraded riparian buffer. Two sites were adjacent to extensive wetland or intact riparian buffer (Bukanaga and Kyayi), and two sites (Mpamuguju and Nyanzi) adjacent to intact riparian buffer but situated on river mouths draining cropland dominated catchment. The sites adjacent to degraded riparian buffers had croplands separated from water by a small strip of wetland vegetation (papyrus reeds) of <15m. The sites adjacent to extensive wetland were considered near pristine or less degraded. These still held extensive wetlands coverage within 200 m from the shoreline, consistent with the national guidelines for protecting at least 100 to 200 m buffer zone around lakes and 30 to 100m around rivers or streams (National Environment (Wetlands; River Banks and Lake Shores Management) Regulations 2000). The sites situated on rivers were referred to as riverine, with extensive wetland coverage in the riparian buffers but, unlike less degraded areas, have rivers directly draining adjacent catchment dominated by croplands. We captured fish using a boat seine, a modification of a beach seine (Witte and Van Densen 1995). The seine net used had three main parts including wings, the bunt and a holding bag of 51mm, 25.5mm and 8mm mesh sizes, respectively. The net was set as a round-haul at about 100 m from the shoreline with one end of the line held at 10-15m from the shoreline to avoid obstacles such as tree stumps that damage nets. The sampling was conducted for a year at four different random times: October 2016, January, March, June and October 2017. At each sampling site, three hauls were conducted. Subsequent hauls were done in similar areas as much as possible for standardization. One riverine site, Nyanzi, was not sampled in October 2016 because it was not accessible. At every time of sampling, fish captured in the three hauls at each site were treated as one sample.

Quality Control

The validity of scientific names was based on FishBase, and Eschmeyer’s catalogue of fishes (Froese & Pauly, 2019; Fricke et al. 2019).

Method steps

1. The validity of scientific names was based on FishBase, and Eschmeyer’s catalogue of fishes (Froese & Pauly, 2019; Fricke et al. 2019).

Fish taxa identified to genus and species

1. Clarias gariepinus
   rank: species
2. Coptodon zillii
   rank: species
3. Enteromius
   rank: genus
4. Haplochromis
   rank: genus
5. Oreochromis niloticus
   rank: species
6. Oreochromis leucostictus
   rank: species
7. Protopterus aethiopicus
   rank: species

The resource covers Lake Wamala. The lake is a UNEP designated environmental change hotspot (https://na.unep.net/atlas/webatlas.php?id=391).