Fisheries of western Lake Tanganyika in March 2024

Study Extent

The field area was located at the northwestern part of Lake Tanganyika along the Congolese shores near and north of Baraka City in the territory of Fizi. Due to logistic constraints and field accessibility (human activities disruption or not, fishing effort) and safety, the sampling and survey sites consisted of main villages established along the coastline in these areas. This region has a tropical humid climate characterized by an alternation of wet and dry seasons and is currently subject to physical factors at different scales. All those beach fishing sites were easily accessible from each one by boat and have fishing activities as main occupation. Whenever necessary, each main site was split up into different small sub-sites according to the type of littoral habitat of the lake, i.e., sandy, rocky, mixed, and the type of fishing practices. The critical habitat of a fish species is defined as a geographic or physical area essential to the realization of the life cycle (Lévêque 1995). However, the knowledge of local communities and advices of experienced local fishermen were considered during the fish sampling in each site. At the field of investigation, some localities of high human influences are undergoing alterations (water pollution and sedimentation, fishing with unsuitable fishing gears and techniques and deforestation) with some fish species exposed to human pressures or extinction in the future.

Sampling

Collections of fish samples were performed once or twice per site during the study period using complementary methods in each selected station. Individuals fish species were collected in different habitats within the selected sites from local commercial catches of fishermen using their different fishing gears: gillnets of different mesh sizes and widths, beach seines and liftnets with mixed mesh sizes, gillnets with various techniques (i.e., monofilament, dormant, encircling and deep gillnets, …) and illegal mosquito nets of smaller mesh-sizes (02-03 mm). These various gears were surveyed in each sampling day and site according to the fishing habitat (lake substratum) and lake site (inshore vs. offshore). We recorded the features of each net directly at the sampling site such as the length, width (near 1.00 m) and mesh-size (near 1.00 mm) using a measuring tape or decametre. We noted the fishing depth, the duration as well as the effort (e.g., number of nets per active fishing unit, number of fisherman and net hauls) for each gear. The presence of each gear at a site allowed assessing the rate of fishing activity and fish distribution within the sampling habitats. The type of fishery and net, the numbers of fishermen involved per trip and per fishing unit were recorded and are discussed in relation to the type of gear used. After each fishing trial, fresh weight (in kg) of each sample was measured per fishing gear and number (net hauls per trip) recorded whenever possible. For each type of fishing, fish samples with a selection of species were usually bought from fishermen, and preliminary sorted at sampling sites (as fishermen did not deliver their entire fish capture) by species and after being weighed. The fish samples (handful) were collected and killed and preserved into ethanol (75%) and then fixed in formaldehyde (10%) to slow decomposition of organs. All fish species captured were identified, weighed and counted following the fishing habitat and effort. The samples were separated into smaller bags by type of fishing-gear, site and other parameters of the fishing-effort and environment and kept in 10% formaldehyde for subsequent analysis in the laboratory

Quality Control

Quality control was implemented through the steps and process outlined for all staff at the Center for Research on Hydrobiology. In addition, there was internal quality control measures that were put in place such as routine monitoring and evaluation of project progress.

Method steps

1. At the laboratory of Biology at the Centre de Recherche en Hydrobiologie (CRH, Uvira, DR Congo) each sample was re-sorted into species by fishing gear and habitat or fishing effort and each species identified following available books and/or keys (Fryer and Iles 1972; Axelrod et al 1977; Poll 1956, 1986; Brichard 1978, 1989; Eccles 1992; Konings 2015; Fermon et al 2007) Then, specimens were sorted by species, counted and the total, standard lengths (TL and SL) and the body height (BH) were measured (nearest 0.1 mm). These measurements and measuring techniques of fish were executed according to Barel et al. (1977), Eccles (1992), Snoeks (1994), Snoeks et al (1994), Snoeks et al (1997), Snoeks (2000) and Hanssens and Snoeks (2003). Sex was determined by exanimating the genital papillae and other external body feature such as coloration patterns (Snoeks 2000). For details in the sex, fish were dissected to determine the maturity stages of gonads following De Kimpe (1964), Micha (1973), Plisnier (1990). Each fish was then weighed (using various scales following species and individual sizes), the viscera and the gonads removed, and weighed (nearest 0.001g) and the body re-weighed to calculate the gonado-somatic index (GSI).

1. Chordata
   rank: phylum
2. Cichlidae
   rank: family
3. Poeciliidae
   rank: family
4. Bagridae
   rank: family
5. Clupeiformes
   rank: order
6. Actinopterygii
   rank: class
7. Animalia
   rank: kingdom
8. Perciformes
   rank: order
9. Latidae
   rank: family
10. Clupeidae
    rank: family
11. Cichliformes
    rank: order
12. Cyprinodontiformes
    rank: order
13. Siluriformes
    rank: order

Western Lake Tanganyika within the boundaries of the Democratic Republic of the Congo.