Home | | The Diversity of Fishes: Biology Evolution and Ecology | The living coelacanths, at least for now

Chapter: The Diversity of Fishes: Biology, Evolution, and Ecology: Living representatives of primitive fishes

Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail

The living coelacanths, at least for now

When Marjorie Courtenay-Latimer went down to the docks of East London, South Africa, to wish the crew of the trawler Nerine a happy Christmas, she could not have had a notion of how this friendly gesture would completely change her life and the course of 20th century natural science.

The living coelacanths, at least for now

 

When Marjorie Courtenay-Latimer went down to the docks of East London, South Africa, to wish the crew of the trawler Nerine a happy Christmas, she could not have had a notion of how this friendly gesture would completely change her life and the course of 20th century natural science. Captain Goosen had saved several fishes from his recent catch that he thought she might want for the East London Museum’s collections. Included in the pile was a curious, 1.5 m long fish that was “. . . pale mauvy blue with iridescent silver markings. . . . Was it a lungfish gone balmy?” (Courtenay-Latimer 1979, p. 7).

 

Ms. Courtenay-Latimer sent a rough drawing and description of the fish to Dr. J. L. B. Smith, a South African chemist turned ichthyologist (Fig. 13.8). The Christmas mail and summer rains delayed communication between Courtenay-Latimer and Smith and it was almost 2 weeks before a telegram arrived from Smith desperately urging Courtenay-Latimer to preserve as much of the fish as possible. Smith suspected the fish was a coelacanth, but it seemed so implausible. Unfortunately, the size of the fish, the summer heat, and bad luck conspired against them and only the skin was preserved and mounted by a taxidermist. On February 16, 1939, Smith finally managed to drive to East London and view the mount and confi rm that the fish was without doubt, “scale by scale, bone by bone, fin by fin . . . a true Coelacanth” (Smith 1956, p. 41). Smith named the fish Latimeria chalumnae in honor of Ms. Courtenay-Latimer and the Chalumna River off which the fish was captured. The hunt for a second, more complete specimen began immediately.


Figure 13.8

Marjorie Courtenay-Latimer’s drawing and description of the first coelacanth, as sent to J. L. B. Smith. Key features pointed out by Courtenay-Latimer included bony plates on the head and the extra median lobe in the caudal fin. From Smith (1956), used with permission.


 

Despite a sizable promised reward, intensive collecting efforts along much of the eastern coastline of Africa, and deepsea trawling around the world, a second specimen was not obtained for 14 years. The second coelacanth was slightly different in that it lacked a first dorsal fin and a caudal fringe, probably having lost them to a shark. Smith erected a new genus, Malania, in honor of the then Prime Minister of South Africa, D. F. Malan, who loaned Smith a plane to fly to the capture locale and snatch the fish away from French authorities. As Malan was also the architect of the racial separation doctrine of apartheid in South Africa, Smith’s “patronymic” was viewed as a distasteful political expediency by many outsiders. Later analysis and additional specimens confi rmed that only one coelacanth species existed:Malania was abolished in favor of Latimeria.

 

The second and all but a half dozen of the known 175 specimens of L. chalumnae have been caught off the coast of the Comoros Islands (now the Republic of Comores), a small island group in the Indian Ocean that lies between the island of Madagascar and Mozambique in East Africa. The fish have been captured by hook-and-line fishermen off the western coasts of two islands, Grand Comoro and Anjouan. The fish are usually captured as bycatch of the fishery for Oilfish (Ruvettus pretiosus, Gempylidae). The coelacanth has the native name “Gombessa” and is not a desirable food fish (the often-cited fact that the scales are used for roughening bicycle tire tubes is erroneous; Stobbs 1988). The fish are limited to areas of relatively recent, steep lava flows that are perforated with small caves. By day the fish rest in caves at depths between 180 and 250 m (Fricke et al. 1991b). In the evening, they move into deeper water (200–500 m) to feed on small fishes, which they capture via a suction–inhalation mechanism, much like a Giant Sea Bass (Fricke & Hissmann 1994). The relatively restricted depth range may relate to temperature preferences of 18–23°C and reflect the oxygen saturation pro perties of coelacanth blood, which functions poorly in warmer, less oxygen-rich surface waters (Hughes & Itazawa 1972).

 

Specimens range in size from 42 to 183 cm in length and weigh from 1 to 95 kg, the largest individuals being female (Bruton & Coutouvidis 1991). Age estimates indicate that coelacanths live from 20 to as much as 40–50 years (Bruton & Armstrong 1991). Females do not mature until 15 years old, and gestation may require 3 years, the longest of any known vertebrate (Froese & Palomares 2000). Intensive efforts have yet to reveal other populations around the Comoros Islands, although individual animals have been caught in trawls and gillnets off Mozambique, southern Madagascar, Kenya, and the Tanzanian coast (De Vos & Oyugi 2002; www.dinofish.com). An alarming 29 fish – including six in one night – were captured off Tanzania between 2003 and 2006 (Tony Ribbink, pers. comm.). In 2000, a second East African population was discovered by divers off the KwaZulu-Natal, South Africa coast (Venter et al. 2000; www.acep.co.za). Even more exciting was the discovery of another coelacanth species in Indonesia in 1997.

 

The world took notice of Latimeria in a big way, perhaps too big. The hype and publicity surrounding the Comoran coelacanths have posed a serious threat to their continued existence. The total Comoran population is estimated at 200–600 individuals and is thought to be declining (Fricke et al. 1991a; Fricke & Hissmann 1994; Hissmann et al. 1998). Small clutch size and late maturation indicate a slow reproduction rate, which means individuals are replaced slowly in a population. Between 1952 and 1992, at least 173 individuals were captured, most as research and display material for museums (Bruton & Coutouvidis 1991). Unfortunately, a black market for coelacanths also developed because of the animal’s freak appeal (Stobbs 1988; Bruton & Stobbs 1991). Celebrity transformed a bycatch fishery into a directed fishery; a single coelacanth was worth US$150, or about 3–5 years’ income to a fisherman. The fish eventually sold for $500–2000 on the open market.

This directed fishery was eliminated when the Comoran goverment outlawed the capture of coelacanths, but incidental captures still occur at the rate of 5–10 fish per year, which could represent as much as 5% of the adult population captured annually (H. Fricke, pers. comm.).

 

All these circumstances – slow growth and maturation, small clutch size, limited habitat and geographic range, limited recruitment, small and perhaps decreasing population size, intense exploitation – indicate that coelacanths are particularly vulnerable and threatened by extinction. International conservation efforts were initiated: the coelacanth was listed as Critically Endangered by the International Union for the Conservation of Nature (IUCN) and placed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), thereby outlawing commercial trade by signatory nations. A Coelacanth Conservation Council was formed to coordinate and promote research on and conservation of coelacanths; this organization evolved into the African Coelacanth Ecosystem Programme . Efforts have also focused on providing alternative fishing methods and species for Comoran fishers (see Coelacanth Rescue Mission, www.dinofish.com) and to discourage ongoing, well-financed efforts at capturing live specimens for display in public aquaria.

 

The Coelacanth Conservation Council proposed that the coelacanth be adopted as the international symbol of aquatic conservation, equivalent to the panda’s status for terrestrial conservation, because “. . . Coelacanths occupy a unique place in the consciousness of man: they represent a level of tenacity and immortality which man will never achieve during his short stay on earth” (Balon et al. 1988, p. 274) (Fig. 13.9).


Figure 13.9

Coelacanths are as cuddly as pandas. (A) The Coelacanth Conservation Council’s (CCC) image of a coelacanth, proposed to serve as the World Wildlife Fund’s symbol for marine conservation, the panda representing terrestrial conservation. (B) An ichthyology student was moved by the plight of the coelacanth and had the CCC image tattooed on her hip. Photo by G. Helfman, courtesy of G. Hendsbee.



Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail


Copyright © 2018-2020 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.