The South African Coelacanths — an Account of What Is Known After Three Submersible Expeditions
Total Page：16
File Type：pdf, Size：1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by South East Academic Libraries System (SEALS) Coelacanth Research South African Journal of Science 102, September/October 2006 491 The South African coelacanths — an account of what is known after three submersible expeditions Karen Hissmanna,b*, Hans Frickeb, Jürgen Schauera,b, Anthony J. Ribbinkc, Mike Robertsd, Kerry Sinkc and Phillip Heemstrac as part of the African Coelacanth Ecosystem Programme. Using the manned submersible Jago, the habits, distribution and The primary objective of surveys in South African waters was number of coelacanths within all main submarine canyons of the to assess the distribution and number of the coelacanths in the Greater St Lucia Wetland Park were studied during 47 survey dives, canyons of the Greater St Lucia Wetland Park (GSLWP) World with a total bottom time of 166 hours at depths ranging from 46 to Heritage Site. This census should assist the authorities in 359 m, between 2002 and 2004. Twenty-four individuals were compiling a management plan for the conservation of a fish that positively identified from three of the canyons, primarily from inside is, on the one hand, accessible for specially trained sport divers 15 caves at or close to the canyon edges at depths of 96–133 m with and, on the other,ranked as rare and endangered and therefore water temperatures between 16 and 22.5°C. The population size of requiring protection. Determination of whether the group of coelacanths within the canyons is assumed to be relatively small; coelacanths observed by the divers is resident in the Sodwana coelacanths are resident but not widespread nor abundant within canyons and whether they constitute a viable population was a the park. further important investigation. Acoustic telemetry of a single tagged fish gave insights into activity and movement patterns. Scale samples taken off coelacanths in situ by the submersible Introduction provided small amounts of tissue for genetic analyses. We For more than 40 years, it was assumed that the Comoros summarize present understanding of the ecology and behaviour Archipelago, located in the Western Indian Ocean between of the Sodwana coelacanths compared with findings from other Mozambique and Madagascar, was the only natural home of the locations. living coelacanth. Specimens that were caught off East London,1 2 3 Mozambique and Madagascar were assumed to be strays Methods swept away from the Comoros by the powerful currents along the coast of eastern Africa.4 Between 1995 and 2001, four coela- Diving facilities canths were caught off the southwest coast of Madagascar Coelacanths of the Comoros and South Africa usually live at (R. Plante and B. de Gaulejac, pers. comm.), and additional spec- depths of and below 100 m. The study of coelacanths thus imens were recently caught in bottom trawl and deep-water requires sophisticated technology like manned submersibles, shark nets off Kenya5 and Tanzania.6 With each occasional catch remotely operated vehicles (ROVs) or specially trained deep- it became doubtful that these fish were all recent strays from the water divers with mixed gas or re-breather equipment. The Comoros. In November 2000, the discovery of a group of coela- German research submersible Jago, which has an operating canths by scuba divers in submarine canyons off South Africa7 depth of 400 m, was used in extensive surveys off Sodwana demonstrated that Western Indian Ocean coelacanths are not re- (Fig. 1). The high manoeuvrability of the craft and an extensive stricted to the Comoro Islands. bottom time, both essential for searching large areas and to South African coelacanths are found in an area that is located inspect narrow niches, caves and overhangs, make Jago an ideal within the sphere of influence of the Agulhas Current, one of the tool for coelacanth surveys. The submersible was operated from strongest ocean currents in the world.8 The physical environment the FRS Algoa, which was modified for this purpose by the South therefore initially seemed to be different from the conditions African Department of Environmental Affairs and Tourism. found for the Comoran coelacanth habitat. The divers sighted the fish at the edge of Jesser Canyon at 100 m, almost 100 m Study site shallower than the depth at which coelacanths live at the The marine protected area of the GSLWP contains 12 large and Comoros.7 Finding coelacanths at different locations provides numerous small submarine canyons that run perpendicular to opportunities for comparative studies on the ecological require- the shore along a stretch of coastline approximately 78 km in ments of the fish, lifestyle and activity patterns at different habi- length. The canyons were identified and mapped by means of a tats, and on genetic similarities and differences between and multibeam bathymetric survey in 2002.16 Canyon heads breach within populations. the continental shelf at distances of 2–4 km from shore at depths Most information on the life history and ecology of the of 90–120 m. For more details on the geomorphology of the living coelacanths known to date has been derived from in situ canyons, see Ramsay and Miller in this issue.16 Table 1 lists the 13 observations at Grand Comoro,9–13 the largest island of the canyons explored. volcanic archipelago. The results of these studies were used to design coelacanth surveys in Indonesia14 and South Africa Coelacanth census and behavioural observations From observations at the Comoros it is known that coelacanths a Leibniz Institute for Marine Sciences, 14148 Kiel, Germany. spend the day in caves,11 where they are usually exposed to water bMax-Planck-Institut für Verhaltensphysiologie, 82319 Seewiesen, Germany. cSouth African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, temperatures of about 20°C or less. The search for coelacanths off South Africa. South Africa therefore focused within the same temperature dMarine and Coastal Management, Ocean Environment Section, Private Bag X2, Rogge Bay 8012, South Africa. range on those areas likely to have caves or other shelters. Caves *Author for correspondence. E-mail: [email protected] and overhangs were located by cruising along a set depth 492 South African Journal of Science 102, September/October 2006 Coelacanth Research able boat and from the FRS Algoa. Most tracking took place at night when coelacanths are known to be more active,18 with a few fixes taken on fish position during the day when possible. Collection of environmental data Data on the physical environment of coelacanths were collected during each dive by a temperature sensor attached to the submersible’s keel and by a CTD (conductivity, temperature, depth) device at Jago‘s stern. The CTD continuously recorded depth, temperature, salinity, oxygen and conductivity at intervals of 20 s. Visual observations of particulate floating matter, flexible soft corals, and other sessile animals revealed preliminary infor- mation on currents within the coelacanth habitat. No quantitative measurements of currents inside the canyons were available. Visual and video observations were used for a preliminary assessment of fish density and species identification within the coelacanth habitat. A detailed account of the fish community supported by the canyon habitats off Sodwana is presented in this issue.19,20 Fish counts were also conducted to estimate the abundance of potential prey fish (coelacanths are piscivorous) during the 2004 cruise, but results are not yet available. The extensive surveys for coelacanths provided valuable data on the biodiversity of the megabenthos and fishes within the coelacanth habitat and also geomorphological information. Two preliminary reports on the coelacanth habitat and the canyon morphology were compiled by the first author after the 2002 and 2003 cruises Fig. 1. Research submersible Jago being launched off Sodwana Bay from the FRS (unpublished reports, listed after references). Algoa. (Photograph: James Stapley.) Scale sampling contour mainly without artificial light to increase the range of Tissue samples were required for study of population genetics, vision in twilight. genome and stable isotope analysis. Coelacanths possess large All encounters with coelacanths were documented on video scales that overlap. The pigmented epithelium that covers the for later individual identification. From studies at the Comoros it exposed part of the scale is a sufficient source for nuclear-DNA is known that coelacanths show fidelity to various caves, which analysis. The Jago team developed a non-injurious method to they visit regularly over several years.12 Resighting known indi- collect scales from coelacanths in their natural environment. It viduals allows investigations of home range, movement, space includes a 60-cm-long cylindrical steel barrel mounted on the utilization, intra-species interaction, group composition and life submersible’s manipulator arm, a 70-mm-long cylindrical PVC patterns.11,12 dart that carries three short barbed tips at one end, and a In order to follow the coelacanths’ nocturnal movements, the 60-cm-long nylon string that connects the projectile with the air German team developed a minimally intrusive method to tag gun. The projectile is shot at the tail or flank of the fish from a fish in situ from the submersible.17 A depth-encoding ultrasonic distance of about 20 cm from the end of the barrel. The barbs transmitter is applied by dart to the fish by a pneumatic gun penetrate only the thick scales. A short pull on the nylon line is attached to the submersible’s manipulator arm. The tag falls off sufficient to dislodge the scales from the fish. Because the scales after few weeks. The acoustic signals emitted by the tag are overlap, up to three scales can be collected with a single shot. It is detected at the surface by a directional hydrophone connected not possible to recover the scales and reload the air gun at depth, to a depth-decoding ultrasonic receiver.