Fisheries of Lake Tanganyika

Study Extent

The field area was located at the northwestern part of Lake Tanganyika along the Congolese shores in Ubwari area (from Nguma to Mizimu point) and Baraka City (Mwandiga and Mwemezi sites) in the territory of Fizi (4°18′4″S, 28°56′39″E). Due to logistic constraints and field accessibility (human activities disruption or not, fishing effort) and safety, the sampling and survey sites consisted of at least 8 main villages established along the coastline in these areas including 2 in Baraka (Mwemezi and Mwandiga) and 6 in Ubwari (Nguma, Kazimia, Buma, Kihimino, Mwayenga, and Dine/Mizimu). 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 from March to May 2022 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).

All fish were identified to genus or species.

1. Auchenoglanis occidentalis
   rank: species
2. Bagrus docmak
   rank: species
3. Bathybates elongatus
   rank: species
4. Bathybates fasciatus
   rank: species
5. Bathybates graueri
   rank: species
6. Bathybates minor
   rank: species
7. Benthochromis tricoti
   rank: species
8. Boulengerochromis microlepis
   rank: species
9. Callochromis
   rank: genus
10. Callochromis melanostigma
    rank: species
11. Cardiopharynx shoutedeni
    rank: species
12. Chrysichthys graueri
    rank: species
13. Chrysichthys sianenna
    rank: species
14. Ctenochromis horei
    rank: species
15. Cyathopharynx furcifer
    rank: species
16. Cyphotilapia frontosa
    rank: species
17. Cyprichromis microlepidotus
    rank: species
18. Gnathochromis pfefferi
    rank: species
19. Grammatotria lemairii
    rank: species
20. Haplochromis burtoni
    rank: species
21. Hemibates stenosoma
    rank: species
22. Lamprichthys tanganicanus
    rank: species
23. Lamprologus callipterus
    rank: species
24. Lates microlepis
    rank: species
25. Lates stappersii
    rank: species
26. Lepidiolamprologus attenuatus
    rank: species
27. Lepidiolamprologus cunningtoni
    rank: species
28. Lepidiolamprologus elongatus
    rank: species
29. Lepidiolamprologus marlieri
    rank: species
30. Limnochromis auritus
    rank: species
31. Limnothrissa miodon
    rank: species
32. Limnotilapia dardennii
    rank: species
33. Lobochilotes labiatus
    rank: species
34. Malapterurus electricus
    rank: species
35. Mastacembelus
    rank: genus
36. Mastacembelus plagiostomus
    rank: species
37. Neolamprologus brichardi
    rank: species
38. Oreochromis leucostictus
    rank: species
39. Oreochromis tanganicae
    rank: species
40. Perissodus microlepis
    rank: species
41. Petrochromis
    rank: genus
42. Simochromis
    rank: genus
43. Simochromis diagramma
    rank: species
44. Stolothrissa tanganicae
    rank: species
45. Telmatochromis dhonti
    rank: species
46. Trematocara
    rank: genus
47. Trematocara variabile
    rank: species
48. Tylochromis polylepis
    rank: species
49. Xenotilapia
    rank: genus
50. Xenotilapia sima
    rank: species

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