Lake Tanganyika

Lake Tanganyika(/ˌtæŋɡənˈjiːkə,-ɡæn-/TANG-gən-YEE-kə, -⁠gan-;Kirundi:Ikiyaga ca Tanganyika) is anAfrican Great Lake.It is thesecond-largest freshwater lake by volumeand thesecond deepest, in both cases afterLake BaikalinSiberia.It is the world's longest freshwater lake.The lake is shared among four countries—Tanzania, theDemocratic Republic of the Congo(the DRC),Burundi, andZambia—with Tanzania (46%) and the DRC (40%) possessing the majority of the lake. It drains via the Lukuga River into theCongo Riversystem, which ultimately discharges atBanana, Democratic Republic of the Congointo theAtlantic Ocean.
Lake Tanganyika is situated within theAlbertine Rift, the western branch of theEast African Rift, and is confined by the mountainous walls of the valley. It is the largestrift lakein Africa and the second-largest lake by volume in the world. It is the deepest lake in Africa and holds the greatest volume of fresh water on the continent, accounting for 16% of the world's available fresh water. It extends for 676 km (420 mi) in a general north–south direction and averages 50 km (31 mi) in width. The lake covers 32,000 km(12,000 sq mi), with a shoreline of 1,900 km (1,200 mi), a mean depth of 572 m (1,877 ft) and a maximum depth of 1,471 m (4,826 ft) (in the northern basin). It holds an estimated 18,750 km(4,500 cu mi) volume of water.
Thecatchment areaof the lake is 231,000 km(89,000 sq mi). Two main rivers flow into the lake, as well as numerous smaller rivers and streams (whose lengths are limited by the steep mountains around the lake). The one major outflow is theLukuga River, which empties into theCongo Riverdrainage. Precipitation and evaporation play a greater role than the rivers. At least 90% of the water influx is from rain falling on the lake's surface and at least 90% of the water loss is from direct evaporation.
The major river flowing into the lake is theRuzizi River, formed about 10,000 years ago, which enters the north of the lake fromLake Kivu.TheMalagarasi River, which is Tanzania's second largest river, enters the east side of Lake Tanganyika.The Malagarasi is older than Lake Tanganyika, and before the lake was formed, it probably was a headwater of theLualaba River, the main Congo River headstream.
The lake has a complex history of changing flow patterns, due to its high altitude, great depth, slow rate of refill, and mountainous location in a turbulently volcanic area that has undergone climate changes. Apparently, it has rarely in the past had an outflow to the sea. It has been described as "practicallyendorheic" for this reason. The lake's connection to the sea is dependent on a high water level allowing water to overflow out of the lake through the Lukuga River into the Congo.When not overflowing, the lake's exit into the Lukuga River typically is blocked by sand bars and masses of weed, and instead this river depends on its own tributaries, especially the Niemba River, to maintain a flow.
The lake may also have at times had different inflows and outflows; inward flows from a higherLake Rukwa, access toLake Malawiand an exit route to theNilehave all been proposed to have existed at some point in the lake's history.
Lake Tanganyika is anancient lake, one of only twenty more than a million years old. Its three basins, which in periods with much lower water levels were separate lakes, are of different ages. The central began to form 9–12 million years ago (Mya), the northern 7–8 Mya and the southern 2–4 Mya.
The lake's water isalkalinewith apHaround 9 at depths of 0–100 m (0–330 ft).Below this, it is around 8.7, gradually decreasing to 8.3–8.5 in the deepest parts of Tanganyika.A similar pattern can be seen in theelectric conductivity, ranging from about 670 μS/cm in the upper part to 690 μS/cm in the deepest.
Surface temperatures generally range from about 24 °C (75 °F) in the southern part of the lake in early August to 28–29 °C (82–84 °F) in the late rainy season in March—April.At depths greater than 400 m (1,300 ft), the temperature is very stable at 23.1–23.4 °C (73.6–74.1 °F).The water has gradually warmed since the 19th century and this has accelerated withglobal warmingsince the 1950s.
The lake isstratifiedand seasonal mixing generally does not extend beyond depths of 150 m (490 ft).The mixing mainly occurs asupwellingsin the south and is wind-driven, but to a lesser extent, up- and downwellings also occur elsewhere in the lake.As a consequence of the stratification, the deep sections contain "fossil water".This also means it has nooxygen(it isanoxic) in the deeper parts, essentially limiting fish and otheraerobic organismsto the upper part. Some geographical variations are seen in this limit, but it is typically at depths around 100 m (330 ft) in the northern part of the lake and 240–250 m (790–820 ft) in the south.The oxygen-devoid deepest sections contain high levels of toxichydrogen sulfideand are essentially lifeless,except forbacteria.
Lake Tanganyika and its associated wetlands are home toNile crocodiles(including famous giantGustave),Zambian hinged terrapins,serrated hinged terrapins, andpan hinged terrapins(last species not in the lake itself, but in adjacent lagoons).Storm's water cobra, a threatenedsubspeciesof banded water cobra that feeds mainly on fish, is only found in Lake Tanganyika, where it prefers rocky shores.
Lake Tanganyika is home to at least 250endemicspecies ofcichlids,andundescribed specieslikely remain to be discovered.Almost all (roughly 98%) of the lake's cichlid species are found solely there, and nowhere else, thus making it a precious biological resource for the study ofspeciationandevolution.The cichlids of theAfrican Great Lakes, including Tanganyika, represent the most diverse extent ofadaptive radiationin vertebrates.Some of the endemic species do occur slightly into the upperLukugaRiver (Lake Tanganyika's outflow), but any further distribution into theCongo River basinis stemmed purely by geography and chemistry—Tanganyika's lake environment is far more stable and consistent than therapidsand fast-flowing sections of the Congo River. Additionally, Lake Tanganyika's water isalkalineand of a higherpH(which the cichlids prefer), containing a highercalciumand mineral content than the Congo'sacidic,sediment-rich waters, which collect much organic detritus from the surroundingrainforests. In areas of the Congo away from rapids orwhitewater, the accumulated sediment and organic matter creates sections of "blackwater", with a high concentration oftanninsfrom dissolving wood and leaves, creating an environment in which cichlids simply do not thrive.Likewise, many tropical riverine species would likely suffer if exposed to the crisp, alkaline lake water.
Although Lake Tanganyika has fewer cichlid species than LakesMalawiorVictoria—which both have experienced relatively recent explosive speciesradiations(resulting in many closely related species)—,its cichlids are the mostmorphologicallyandgeneticallydiverse.This is linked to the maturity of Tanganyika, as it is far older than the other lakes.Tanganyika has the largest number ofendemiccichlidgeneraof all African lakes.All Tanganyika cichlids are in the subfamilyPseudocrenilabrinae. Of the 10tribesin this subfamily, half are largely or entirely restricted to the lake (Cyprichromini,Ectodini,Lamprologini,LimnochrominiandTropheini),  while another three have species in the lake (Haplochromini,TilapiiniandTylochromini).Others have proposed splitting the Tanganyika cichlids into as many as 12–16 tribes (Bathybatini,Benthochromini,Boulengerochromini,Cyphotilapiini,Eretmodini,Greenwoodochromini,PerissodiniandTrematocarini, in addition to the aforementioned tribes).
Most Tanganyika cichlids live along the shoreline, down to a depth of 100 m (330 ft), but some deep-water species regularly descend to 200 m (660 ft).Trematocaraspecies have, exceptionally, been found at more than 300 m (980 ft), which is deeper than any other cichlid known.Some of the deepwater genera (e.g.,Bathybates,Gnathochromis,HemibatesandXenochromis) have been caught in places virtually devoid of oxygen, and how they are able to survive there is unclear.Tanganyika cichlids are generallybenthic(found at or near the bottom) and/or coastally.No Tanganyika cichlids are trulypelagicandoffshore, except for some of thepiscivorousBathybates.Two of these,B. fasciatusandB. leo, mainly feed onTanganyika sardines.Tanganyika cichlids differ extensively inecology, and include species that areherbivores,detritivores,planktivores,insectivores,molluscivores,scavengers,scale-eatersand piscivores.These dietary specializations, however, have been shown to be variable and subject toopportunisticchanges. That is, many species of Tanganyikan cichlid with specialized diets showed opportunistic, episodic exploitation ofStolothrissa tanganicaeandLimnothrissa miodonwhen prey concentrations were unusually high.The fishes' breeding behavior falls into two main groups: the substrate- or sand-spawners (often in caves or rock crevices) and themouthbrooders.Among the endemic species are two of the world's smallest cichlids,Neolamprologus multifasciatusandN. similis(bothshell dwellers), measuring up to 4–5 cm (1.6–2.0 in),and one of the largest, thegiant cichlid(Boulengerochromis microlepis) at up to 90 cm (3.0 ft).
Many cichlids from Lake Tanganyika, such as species from the generaAltolamprologus,Cyprichromis,Eretmodus,Julidochromis,Lamprologus,Neolamprologus,TropheusandXenotilapia, are popular aquarium fish due to their bright colors and patterns, and interesting behaviors.Recreating a Lake Tanganyikabiotopeto host those cichlids in a habitat similar to their natural environment is also popular in the aquarium hobby, with many species today being bred in captivity successfully.
Lake Tanganyika is home to more than 80 species of non-cichlid fish and about 60% of these are endemic.
The open waters of the pelagic zone are dominated by four non-cichlid species: Two species of "Tanganyika sardine" (Limnothrissa miodonandStolothrissa tanganicae) form the largestbiomassof fish in this zone, and they are important prey for theforktail lates(Lates microlepis) andsleek lates(L. stappersii).Two additional lates are found in the lake, theTanganyika lates(L. angustifrons) andbigeye lates(L. mariae), but both these are primarily benthic hunters, although they also may move into open waters.The four lates, all endemic to Tanganyika, have been overfished and larger individuals are rare today.
Among the more unusual fish in the lake are the endemic,facultativelybrood parasitic"cuckoo catfish", including at leastSynodontis grandiopsandS. multipunctatus.A number of others are very similar (e.g.,S. lucipinnisandS. petricola) and have often been confused; it is unclear if they have a similar behavior.The facultative brood parasites often lay their eggs synchronously with mouthbroding cichlids. The cichlid pick up the eggs in their mouth as if they were their own. Once the catfish eggs hatch the young eat the cichlid eggs.Six catfish genera are entirely restricted to the lake basin:Bathybagrus,Dinotopterus,Lophiobagrus,Phyllonemus,PseudotanganikallabesandTanganikallabes.Although not endemic on a genus level, six species ofChrysichthyscatfish are only found in the Tanganyika basin where they live both in shallow and relatively deep waters;in the latter habitat they are the primary predators and scavengers.A uniqueevolutionary radiationin the lake is the 15 species ofMastacembelusspiny eels, all but one endemic to its basin.Although other African Great Lakes haveSynodontiscatfish, endemic catfish genera andMastacembelusspiny eels, the relatively high diversity is unique to Tanganyika, which likely is related to its old age.
Among the non-endemic fish, some are widespread African species but several are only shared with the Malagarasi and Congo River basins, such as theCongo bichir(Polypterus congicus),goliath tigerfish(Hydrocynus goliath),Citharinuscitharus,six-banded distichodus(Distichodus sexfasciatus) andmbu puffer(Tetraodon mbu).
A total of 83freshwater snailspecies (65 endemic) and 11bivalvespecies (8 endemic) are known from the lake.Among the endemic bivalves are threemonotypicgenera:Grandidieria burtoni,Pseudospatha tanganyicensisandBrazzaea anceyi.Many of the snails are unusual for species living in freshwater in having noticeably thickened shells and/or distinctsculpture, features more commonly seen in marine snails. They are referred to as thalassoids, which can be translated to "marine-like".All the Tanganyika thalassoids, which are part ofProsobranchia, are endemic to the lake.Initially they were believed to be related to similar marine snails, but they are now known to be unrelated. Their appearance is now believed to be the result of the highly diverse habitats in Lake Tanganyika andevolutionary pressurefrom snail-eating fish and, in particular,Platythelphusacrabs.A total of 17 freshwater snail genera are endemic to the lake, such asHirthia,Lavigeria,Paramelania,Reymondia,Spekia,Stanleya,TanganyiciaandTiphobia.There are about 30 species of non-thalassoid snails in the lake, but only five of these are endemic, includingFerrissia tanganyicensisandNeothauma tanganyicense.The latter is the largest Tanganyika snail and its shell is often used by smallshell-dwelling cichlids.
Crustaceans are also highly diverse in Tanganyika with more than 200 species, of which more than half are endemic.They include 10 species offreshwater crabs(9PlatythelphusaandPotamonautes platynotus; all endemic),at least 11 species of smallatyidshrimp (Atyella,CaridellaandLimnocaridina),an endemicpalaemonidshrimp (Macrobrachiummoorei),about 100ostracods,including many endemics,and severalcopepods.Among these,Limnocaridina iridinaelives inside themantlecavity of theunionidmusselPleiodon spekei, making it one of only two knowncommensalspecies of freshwater shrimp (the other is the sponge-livingCaridina spongicolafromLake Towuti, Indonesia).
AmongRift Valley lakes, Lake Tanganyika far surpasses all others in terms of crustacean and freshwater snail richness (both in total number of species and number of endemics).For example, the only other Rift Valley lake with endemic freshwater crabs are Lake Kivu and Lake Victoria with two species each.
The diversity of other invertebrate groups in Lake Tanganyika is often not well-known, but there are at least 20 described species ofleeches(12 endemics),9sponges(7 endemic), 6bryozoa(2 endemic), 11flatworms(7 endemic), 20nematodes(7 endemic), 28annelids(17 endemic)and the smallhydrozoanjellyfishLimnocnidatanganyicae.
Lake Tanganyika supports a major fishery, which, depending on source, provides 25–40%orc.60% of the animal protein in the diet of the people living in the region.
Lake Tanganyika fish can be found exported throughout East Africa. Major commercial fishing began in the mid-1950s and has, together with global warming, had a heavy impact on the fish populations, causing significant declines.In 2016, it was estimated that the total catch was up to 200,000 tonnes.
It is thought that earlyHomo sapienswere making an impact on the region during theStone Age. The time period of the Middle Stone Age to Late Stone Age is described as an age of advanced hunter-gatherers.
There are many methods in which the native people of the area were fishing. Most of them included using a lantern as a lure for fish that are attracted to light. There were three basic forms. One called Lusenga which is a wide net used by one person from a canoe. The second one is using a lift net. This was done by dropping a net deep below the boat using two parallel canoes and then simultaneously pulling it up. The third is called Chiromila which consisted of three canoes. One canoe was stationary with a lantern while another canoe holds one end of the net and the other circles the stationary one to meet up with the net.
The first known Westerners to find the lake were the British explorersRichard BurtonandJohn Speke, in 1858. They located it while searching for the source of theNile River. Speke continued and found the actual source,Lake Victoria. LaterDavid Livingstonepassed by the lake. He noted the name "Liemba" for its southern part, a word probably from theFipa language.Tanganyikameans "stars" in theLuvale language.
The lake was the scene ofBattle for Lake TanganyikaduringWorld War I. With the aid of theGraf Goetzen, the Germans had complete control of the lake in the early stages of the war. The ship was used both to ferry cargo and personnel across the lake, and as a base from which to launch surprise attacks on Allied troops.It therefore became essential for the Allied forces to gain control of the lake themselves. Under the command of Lieutenant CommanderGeoffrey Spicer-SimsontheBritish Royal Navyachieved the monumental task of bringing two armed motor boatsHMSMimiand HMSToutoufrom England to the lake by rail, road and river to Albertville (since renamedKalemiein 1971) on the western shore of Lake Tanganyika. The two boats waited until December 1915, and mounted a surprise attack on the Germans, with the capture of the gunboatKingani. Another German vessel, theHedwig, was sunk in February 1916, leaving theGötzenas the only German vessel remaining to control the lake.In order to avoid his prize ship falling into Allied hands, Zimmer scuttled the vessel on July 26, 1916. The vessel was later raised in 1924 and renamedMVLiemba.