2017 and 2025 Fish Biomass Data for Lake Malombe, Malawi
Description
The dataset covers the data collected in 2017 and 2025 fish biomass surveys in Lake Malombe in Malawi. The data was collected using blocked sampling stations totalling 45. A local fishing net called Nkacha that catches fish by encircling was used during sampling. Fish samples were processed on board before being returned to the water. Being a multi-species fishery, the Lake Malombe is cichlid-dominated, and fish species dominance changes with time.
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A planked boat without an engine and a standard Nkacha net measuring 150m long by 10m deep was hired and operated by 6 fishing crew members. Another boat carrying the research team followed the fishing crew for guidance and instructions. Data collection forms were designed and used to collect the catch data in addition to other relevant information. Blocks and stations used in the 2017 survey were replicated in the 2025 study. A total of 45 sampling stations were used. The stations were determined using grids on Google Earth to achieve equidistance from one another. The lake, with a 30 km length, was divided into 9 blocks, with each block having a width of approximately 3.8km, which is equivalent to 3 minutes on latitude. A handheld Global Positioning System GPS receiver (extrex 15) was used to locate blocks and stations during the survey. Fish sampling per block was random and fishing started after 8:00 am and finished around 3:00 pm. Upon reaching the station, fishers were instructed to cast the net around the identified station. The GPS Coordinates in decimal degrees were recorded at the shooting and hauling time. The fishing session took an average of 15 minutes from the time of shooting to hauling in the fishing net. Spacing between stations took about 40 to 50 minutes of cruising based on the condition of the day. On average, a total of 6 stations was achieved per day. To speed up the movement between stations, the boat carrying the researchers sometimes would tow the fishing boat to the next station. Before conducting the fish sampling exercise, data enumerators and fishers were informed and oriented on the best handling techniques of the sampled fish. Fishing crew members were strongly warned against hiding some fish samples. The study attempted to keep most of the sampled fish alive by using containers filled with water drawn from the lake. After fishing, all the caught fish were brought to the researchers’ boat for an onboard data collection. Fish catch data were collected following the adapted guidelines of Pauly (1983) and Sparre & Venema (1989) Data recorders sorted the sampled fish by size and identified them at the species level. Fish identification was done by well-trained and experienced taxonomists while refering to relevant field guides and taxonomic keys from Turner (1996) and Konings (2016). Individual total length (mm) and batch weight (g) were recorded on structured data forms. Where fish species were difficult to identify, good-quality photos were sent to fish taxonomy experts like George Turner and Denis Tweddle to help with identification.