Factors behind declining fish catches in Lake Tanganyika

Thursday November 18 2021
Lake pic

A fisherman bargains price with a buyer at a fish market on the shores of Lake Tanganyika. Growing pressure on fishing and climate change are some of the key factors that have seen fish catches diminishing in Lake Tanganyika, Africa’s deepest fresh water lake, experts have shown. PHOTO | FILE

By Rosemary Mirondo

Dar es Salaam. The livelihoods of fishing communities around Lake Tanganyika are under threat and - hence - no longer secure due to a decline in fish catches, especially in the northern part of the lake.

A senior lecturer of the University of Dar es Salaam (UDSM), School of Aquatic Sciences and Fisheries Technology, Mr Paul Onyango, says fish catches have declined by almost a half over the last three decades as a result of overexploitation and climate change.

Africa’s deepest lake is famous for Lates stappersii (“Migebuka”) and Stolothrissa tanganicae (“Dagaa”), and the researcher says there is strong evidence that climate change - which causes reductions in regional winds and warming of the lake surface waters - have significantly reduced the lake’s productivity and fish growth.

The growing human demand for food from fish, and lack of alternative livelihoods, have also been cited as factors that intensify pressure on fishing resulting in overexploitation of available fish stocks.

Mr Onyango was speaking during a media workshop in Zanzibar aimed at enhancing sustainable fisheries management and aquaculture development in Africa. This is in the framework of the programme for accelerated reform of the sector (“Fishgov 2” project).

“It was not clear which factor between climate change and human pressures poses a greater threat. Despite government efforts to reverse the situation through monitoring and regulations, it has not been possible to maintain sustainable harvest levels. Fishing efforts and use of unsustainable fishing methods have continued to increase from year to year, especially in areas that lack alternative livelihoods. Climate change has also contributed to declining conditions for fish productivity,” he said.

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He noted that, as a consequence of these factors, households are food-insecure following the pelagic fishery of Lake Tanganyika that used to consist of six fish species.

According to him, over the past three decades, only three species dominated the catches, namely: Lates stappersii (Migebuka), Limnothrissa miodon (Dagaa-I) and Stolothrissa tanganicae (Dagaa-II).

“While the disappearance of the large Lates species has been linked to overfishing by purse seiners, the persistence of the dagaa and migebuka is mostly related to their life histories. The dagaa live for a maximum of two years and are highly resilient. Migebuka, on the other hand, live for about five years - which makes them somewhat resilient and able to recover from exploitation compared to the larger Lates species, which have life spans of more than 10 years,” he said.

The climate-induced reduction in the lake productivity makes the resilience of dagaa and migebuka unpredictable.

Uncertain food availability, therefore, can cause the fish population to crash, especially when recruitment fails as a result of changing climate conditions.

There has been a significant decline in pelagic fish landings of about 40 percent since 1985, despite an increase in the number of fishing units from about 5,000 to 11,500 and a doubling in the number of fishermen to 26,000 in 2015.

The experts say the fishery has a 35 percent post-harvest loss, meaning that 35 percent of all catches landed get spoiled before consumption.

This is a result of some fishing methods as well as poor handling immediately after capture on the lake and landing at the beach. Presently, fishers use wooden boxes that are not properly customised for long-term storage.

He said proper fish boxes should be insulated plastic which can support the use of ice for immediate preservation after the catch is landed on the boat.

The post-harvest losses are causing further decreases of earnings by the fishermen.

This may be driving increasing fishing pressures in order to offset the effects of declining catches and increased post-harvest losses.

As a result, he said it was imperative to minimize human impacts on the lake, protect local fishermnen by not licensing large fishing vessels to prevent further overfishing, protect breeding grounds and establish a closed season in cooperation with fishing stakeholders.

There is also a need to develop alternative livelihoods in collaboration with local fishing stakeholders to reduce fishing pressures on the lake, and provide support to help fishermen to replace traditional wooden fish boxes with insulated iceboxes to reduce post-harvest loss.

Also, it is important to train fishermen, fish traders, and processors to handle, process and pack fish to increase quality and shelf life, and thus income of all people. More efforts must also be done to improve food security by investing in land-based aquaculture and provide support for continued monitoring of lake conditions and fisheries, including high frequency data acquisition technology, electronic catch assessment survey, and hydroacoustic technology.

For his part, East African Community’s (EAC) senior Livestock officer David Balikowa said the EAC fisheries and aquaculture policy of 2018 aimed to promote sustainable fisheries and aquaculture development in order to contribute to food security, nutrition and wealth creation in the EAC partner states.

“The policy goal is to increase fish production and reduce fish post-harvest losses; increase fish per capita consumption and increase annual fish exports,” he said.

Further enhancing the capacity of centres of excellence on management, development, research and sharing data and information; increase intra and inter regional trade in fish and fishery products; and strengthen data, information collection and dissemination.