Effects of Climate Change and Anthropogenic Activities on Algivorous Cichlid Fish in Lake Tanganyika

Introduction

Lake Tanganyika is the second deepest lake in the world, holding approximately 1/6 of the world’s freshwater (Wetzel, 2001). It lies in the East African Rift Valley and is shared by four countries with the shoreline of about 1,800 kms, among these 9percent is in Burundi, 43percentis in the Democratic Republic of the Congo, 37percent is in Tanzania, and 11percent is found in Zambia (Fig. 1). The lake supports the most productive freshwater pelagic fishery, with remarkable cichlids fish diversity with estimated 250 morphologically and behaviourally diverse fish species that mainly inhabit the lake’s littoral habitats (Snoeks, 2000). Most of the fish in the rocky littoral zone of Lake Tanganyika are algivorous cichlids that graze on the attached algae (periphyton), which are found on the rocky shore habitats of the littoral zone (Takeuchi, Ochi, Kohda, Sinyinza& Hori, 2010). In general, Lake Tanganyika ecosystems represent biodiversity hotspots of endangerment (Dudgeon et al., 2006) because of their critical contribution to global biodiversity.

Lake Tanganyika is a significant source of food and livelihood to millions of people dwelling inside and outside of its basin. The basin is rich in minerals and fertile soils. The main economic activities of the 10 million people living in the lake’s catchment area are small-scale agricultural activities (Nkotagu, 2008) including farming of crops such as maize, tobacco, rice, sugarcane, coffee, beans, groundnuts, cassava; and keeping of livestock such as cattle and goats for their livelihood. The lake is also used asa means of transportation of goods and generation of hydroelectric power, communication, and a source of potable water for the sustenance of human, livestock, and agricultural activities (Coulter, 1991). It is also a source of revenue from fishing and ecotourism in the riparian countries bordering the lake.

The fisheries of Lake Tanganyika are by far the most important source of animal protein for human consumption along the lake. The lake supplies between 25-40 percent of the protein needs of the local population in the four riparian countries (Mölsä, Reynolds, Coenen, &Lindqvist, 1999). About 45,000 people are directly involved in the lake fisheries which constitutes between 55-90percent of the commercial fishery and 80-99percentof the traditional artisanal fishery (Rufli, 2001).

Figure 1.

Geographical location of Lake Tanganyika

Globally, greenhouse gas emission has increased leading to atmospheric concentration of gases such as carbon dioxide, methane, and nitrous oxide. The effects of these gases are likely to be the dominant cause of the observed global warming (Burnett et al., 2011). About 60percent of these emissions have been stored on land, marine, and freshwater systems. This might have increased the pH of both marine and fresh water ecosystems. Moreover, lake water pH is under the (stronger) influence of land and sediment and thus, the effect of atmospheric CO₂may play a relatively minor role. One of the most immediate and obvious effects of global warming is the increase in temperatures around the world. The average global temperature has increased by about 1.4 degrees Fahrenheit (0.8 degrees Celsius) over the past 100 years, according to the National Oceanic and Atmospheric Administration (IPCC, 2018, NOAA,2019)