The coelacanth.

The fleshy lobed pectoral fin of the coelacanth is one of its distinguishing features as a primitive fish.

Caves on the continental slope (200m), a preferred habitat for coelacanth
all photos © Hans Fricke

Coelecanth - Latimeria chalumnae

The coelacanth is possibly the sole remaining representative of a once widespread family of Sarcopterygian (fleshy-finned) fish that were common from 280-100 mya, and were distributed throughout the globe. More than 120 species are known from fossils, and the family was thought to have become extinct during the K-T extinction event, 65 million years ago. Coelecanth were first identified from an English fossil by naturalist Louis Agassiz in 1836 and became known as a distinct taxonomic group in 1844. Two species of coelacanth are alive today, the western Indian Ocean species Latimeria chalumnae, and a more restricted Indonesian species, L. menadoensis.
Coelacanth are most commonly found on sloping continental shelves, below about 100 m depth, where bottom topography such as caves, and canyons/fissures leading into deep water provide shelter for them and habitat for their prey. The submarine canyons of the east and west coasts of the Mozambique channel, and steep volcanic slopes of the Comoros have been the main areas in which they have been found, and more recently on the upper slopes of canyons in the Pemba Channel (Tanga, Tanzania).
Coelacanths can reach almost 2 m and weigh up to 80 kg or more, but are usually somewhat smaller. Males average 165 cm and are smaller than females. They are dark brown/blue with distinctive white flecks that provide camouflage against the backdrop of dark lava and rocky walls encrusted with white oyster shells. The spot patterns can be used by researchers to recognize individuals. Individuals may live as long as 60 years, but this is uncertain. Coelacanths are ovoviparous, giving birth to as many as 26 live young that develop from eggs in the oviduct, feeding off a large yolk sac until birth. Nothing is known about mating behavior or even juvenile habitat.
Coelacanth are opportunistic feeders, on or near the bottom. Stomach contents have included lantern fishes, stout beard fishes, cardinal fishes, cuttlefishes, deep water snappers, squid, deep sea witch eels, snipe eels, swell sharks, and other fishes normally found in their deep reef and volcanic slope.
In 2008, the population of the Comorian coelacanth was estimated to be about 500, and since the first capture of a coelacanth in Tanzania at Kilwa Mnoro in 2003, 80 more specimens have been landed up to October 2010, as well as many more individual captures in Kenya, Mozambique and Madagascar, indicated a widely dispersed population, with some locally dense sub-populations. Genetic studies suggest there may be two distinct populations of coelacanth, though this is not fully confirmed: a southern one centered on the Comoros and extending to southern Tanzania, and a northern one in Tanga, northern Tanzania. If true, the patterns show distinct signs of gene flow to the north, but not in the reverse direction, and the ranges of the populations are consistent with high connectivity throughout the Mozambique channel and unidirectional flow northwards in the East African Coastal Current.

History - In 1938, a living coelacanth was discovered by Marjorie Courtenay-Latimer among specimens in a trawler that had been fishing off East London, South Africa, in the southern WIO. This fish was described by J.L.B. Smith in an atmosphere of scientific excitement, skepticism and doubt. The media considered this to be the zoological discovery of the century. Up till the 1980s coelecanth were still only known from a few locations in the SWIO, with the best-known populations found in the Comoros, where fishermen were familiar with this unusual fish caught in deep-set lines. By the end of the 20th century, the fish was known to be widespread in the WIO, with the northernmost record from Malindi, Kenya, and significant populations in northern Tanzania, several of the Comorian islands and southern Mozambique/northern South Africa. As diving technology has improved, live observation or coelacanths has become possible – first from the submersible GEO, in 1987, and more recently on rebreather diving units, from November 2000.

Threats - The primary threat to coelacanth is demersal fishing on the continental shelf, between about 100 and 400 m. In Comoros, this was primarily using artisanal gears historically, so development of more mechanized fisheries, using motors for offshore fishing, resulted in decreased coelacanth catch in the 1960s. However with increasing numbers of fishers, and greater use of deep gill nets such as in Tanga, Tanzania since 2000, large numbers of coelacanth have been caught from previously unknown populations. The larger numbers reported are also likely due to a greater awareness of the significance of coelacanths, and improved communications, such that catches that might have gone unnoticed previously are now brought to the attention of authorities. Nowhere, however, is there an indication that coelacanths exist in large aggregations.

Fishermen in Tanga, Tanzania, have caught over 30 coelecanth in the last 10 years, likely due to changing fishing techniques and increase pressure, revealing a population previously unknown to science.
© Hassan Kalombo

Conservation - The coelacanth is listed as Critically Endangered on the IUCN Red List, and in Appendix 1 of CITES. The Comoros has been the epicenter of coelacanth conservation from the 1970s onwards, with the most comprehensive efforts to both study and design conservation measures appropriate to this unusual fish. The discovery of coelacanths within the World Heritage Site iSimangaliso in 2000 emphasized the precautionary value of protecting critical sites of high biodiversity value. Since 1987 the Comoros has been the epicenter of coelacanth conservation efforts, led by Dr. Hans Fricke and supported by the Frankfurt Zoological Society and others. In 2002 the African Coelacanth Ecosystem Programme (ACEP) was initiated taking on a trans-frontier, ecosystem based approach to science and management of the coelacanth, with a particular focus on depths between 40 – 1000m in the Mozambique Channel and north to Kenya. In Tanga, Tanzania, the catch of over 30 coelecanth in the decade from 2000 - 2010 led to the formation of the Tanga Coelacanth MPA. Exploration and observational research, conducted by manned submersibles and ROVs, will continue to play a major role in coelacanth studies, alongside biotelemetry, underwater recording systems and physiological probes in order to answer elusive questions.

Key References - Agassiz (1844); Erdmann (2006); Forey (1998); Fricke and Hissmann (1994); Fricke et al. (2000); Fricke et al. (2011); Green et al. (2009); Heemstra et al. (2006); Nikaidoa et al. (2011); Plante et al. (1998); Scott (2006); Smith (1939); Smith (1953); Smith (1956). --> References