|Scientific Name:||Electrolux addisoni|
|Species Authority:||Compagno & Heemstra, 2007|
|Taxonomic Notes:||The four other valid genera of the sleeper ray family Narkidae were published in 1826 (Narke), 1831 (Temera), 1909 (Typhlonarke), and 1921 (Heteronarce), so that finding a new monotypic genus of relatively large, conspicuous (aposematic), inshore, diurnal, and geographic and bathymetrically restricted sleeper ray was quite surprising.|
|Red List Category & Criteria:||Critically Endangered B2ab(ii) ver 3.1|
|Reviewer(s):||Valenti, S.V., Gibson, C.G. & Fowler, S.L. (Shark Red List Authority)|
The Ornate Sleeper Ray (Electrolux addisoni) is a recently described new genus and species of electric ray, known only from a few records on a few sites on the eastern coast of South Africa, over a two decade period. The few sightings have all been at depths of less than 50 m. Little is known of this species' biology, but it is the largest known Narkid. The Ornate Sleeper Ray apparently is restricted to sandy patches of very limited inshore reef habitat off the Eastern Cape and KwaZulu-Natal coasts at five localities. The species' area of occupancy is estimated at less than 10 km², and its habitat is considered to be severely fragmented. The small stretch of highly developed coastline along which it occurs is subject to intensive human habitat modification and destruction. Given the heavy utilization of the species' narrow strip of habitat, a continuing decline in the area, extent and quality of habitat is inferred, warranting an assessment of Critically Endangered B2ab(iii).
|Range Description:||As presently known this conspicuous, diurnal species is restricted to sandy patches of very limited inshore reef habitat off the Eastern Cape and KwaZulu-Natal coasts of South Africa at five localities (Compagno and Heemstra 2007). Known localities are from dive sites off south-central KwaZulu-Natal. These include from southwest to northeast:
1. Coffee Bay, Eastern Cape (ca. 31º58'S, 29º9'E);
2. Manaba Beach, the type locality near Margate (30°51.4'S, 30°23.1'E, 6-12 m);
3. Protea Banks, about 8 km off Shelly Beach near Margate (ca. 30°49.8'S, 30°28.8'E, dive depths ca. 28-35 m);
4. Aliwal Shoal, 4.8 km. off Park Rynie (ca. 30°19.2'S, 30°48'E, dive depths ca. 14-30 m.);
5. Tee (or T-) Barge north of Durban and about 3 km off Virginia Beach (an artificial reef habitat at ca. 29°47'S, 31°05'E, dive depths ca. 20-27 m.).
The Ornate Sleeper Ray (Electrolux addisoni) has only been recorded along approximately 310 km of coastline with a very narrow continental shelf (10-36 km wide to the 200 m isobath), but the few sightings were all inside the 50 m isobath. Manaba Beach is the only place that it has been seen on two occasions (or more).
An estimate suggests the real range may be less than 10 km² as currently known. If the areas where the rays were actually observed were less than 100 m², the area of occupancy could prove far smaller.
Although the Ornate Sleeper Ray may be more wide-ranging than presently known, offshore and inshore areas on the east coast of South Africa have been relatively well-sampled and this species has to be considered a rarity at present until we know otherwise (L.J.V. Compagno pers. obs. 2007).
Native:South Africa (Eastern Cape Province, KwaZulu-Natal)
|FAO Marine Fishing Areas:||
Indian Ocean – western
|Lower depth limit (metres):||50|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Apparently rare, there are no trend data for the Ornate Sleeper Ray because there are so few restricted records over a long time period. This species is mostly known by a handful of sighting and photographic records by recreational SCUBA divers, ichthyologists and professional underwater photographers, as well as from two type specimens procured by spear-fishing divers, over two decades from 1984 to 2004 (Compagno and Heemstra 2007).
A live specimen was photographed in 1984 on a patch of sand on Aliwal Shoal, KwaZulu-Natal, South Africa in 1984 and was immediately recognized as an undescribed species of electric ray, but its familial allocation to the Narkidae and recognition as a new genus didn't come until two specimens were procured twenty years later. The ray was subsequently rediscovered on Protea Banks off Shelly Beach, KwaZulu-Natal in 1997 where a single specimen was videotaped feeding. Another specimen was seen in the late 1990s off the Tee Barge, an artificial reef habitat in north of Durban, while a second specimen was seen at Coffee Bay, Eastern Cape but eluded capture. Two specimens were speared off Manaba Beach near Margate in southern KwaZulu-Natal in 2003 and form the type series. A few additional specimens were sighted at Manaba Beach before the types were collected but numbers are uncertain.
Wallace's (1967) taxonomic review of electric rays from the east coast of southern Africa did not report any material of Electrolux addisoni. E. addisoni was not taken by the South African Marine and Coastal Management's (MCM) research vessel Algoa during Cruise 014 off Mozambique in 1994 with 28 stations on soft bottom at 37 to 500 m depth. The Algoa collected torpedinoids in small numbers including the narkid Heteronarce garmani and the narcinids Narcine rierai and a second species of Narcine close to the Malagasy N. insolita but not E. addisoni. The MCM research vessel Africana did not collect E. addisoni in thousands of inshore and offshore bottom trawl stations at 17-200 m during two decades of fisheries survey (ongoing) on the east coast of South Africa from Cape Agulhas to Port Alfred. However, the smaller narkid Narke capensis was commonly caught by the large fisheries research vessel Africana in this area and between 27 m and 90 m depths (average depth 54.8 m). This occurs in shallow inshore waters in the Western Cape, South Africa, where a diver caught one by hand at 4.5 m depth in False Bay in the Western Cape. Divers have so far not seen E. addisoni from Cape seas south of Coffee Bay, nor at Mozambique dive sites. It also has not been recorded by the Natal Shark Board in the anti-shark nets deployed off numerous beaches off KwaZulu-Natal, although batoids are regular bycatch of the shark nets (S. Dudley pers. comm. to L.J.V. Compagno 2007).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||The Ornate Sleeper Ray occurs in warm-temperate or subtropical waters along a very narrow continental shelf (10 to 36 km wide to the 200 m isobath). The few sightings of the species were all at less than 50 m depth. Found in subtidal environments in sandy and gravely patches on rocky reefs. Apparently sluggish, this sedentary ray belongs to the sleeper ray family.
It is the largest known narkid, with adult males measuring 50-52 cm total length, and is extremely conspicuous because of its spectacular coloration (which is hard to miss on light sandy patches), diurnal foraging activity and boldness when confronted by divers (Compagno and Heemstra 2007).
Little is known of the biology of this ray. Juveniles are unknown, and the only specimens collected to date are adult males.
This species feeds on the substrate and vigorously thrusts its mouth into loose sand or gravel while walking actively on its spread pelvic fins. It may lie motionless on the substrate, but when approached can arch its back, curl its disk, and raise its tail to perform a possible threat-display directed at the photographer.
Like other South African narkids such as Cape Numbfish (Narke capensis), which mostly eats polychaetes (Compagno et al. 1989), and the Natal Electric Ray (Heteronarce garmani) (one specimen examined), which had a stomach filled with mud-balls, this species apparently feeds on infauna or meiofauna. Stomach contents of the paratype included the semi-digested and fragmentary remains of polychaete worms (including a tube-worm) and at least one small shrimp-like crustacean.
Compagno and Heemstra (2007) suggest that the bold color and possible threat display may act as a defense against sharks that feed during the day. The conspicuous dorsal color pattern of the Ornate Sleeper Ray, combined with the ray's possible threat display, may be aposematic (an antipredator adaptation) and indicates that the ray is well-armed with electric organs and should be avoided. On the shallow, well-lit reefs where the Ornate Sleeper Ray has been found, its main potential predators may be large carcharhinoid sharks (requiem sharks, Carcharhinidae, and hammerheads, Sphyrnidae) and lamnoid sharks (ragged-tooth sharks and white sharks). Deepwater electric rays successfully defended themselves from much larger sixgill sharks (Hexanchus) which are apex predators with a broad prey spectrum, and a quick defensive shock apparently minimized damage by aborting such a predator's attack. For the inshore Ornate Sleeper Ray, aposematic coloration and a threat display might prevent a shark attack if the visual warnings are reinforced by a shock.
The species' known habitat and geographic distribution suggest that the Ornate Sleeper Ray could be at risk from human activities including harassment and disturbance by divers as well as fisheries, pollution, and habitat degradation. It occurs on a heavily utilized and narrow strip of habitat with heavy and increasing human utilization including extensive and intensive recreational diving and sport and commercial fishing along with runaway coastal housing development, boating, commercial shipping, holiday-making, beach utilization, shark netting, and extensive pollution and habitat degradation of inshore environments.
There are no known fisheries that target this species or include it as bycatch, although it has potential interest for the aquarium fish trade, and it would make a spectacular aquarium exhibit provided one could collect live specimens and keep them successfully in captivity. Juveniles are unknown, and the only specimens collected to date are adult males.
No conservation measures are in place at present.
Compagno and Heemstra (2007) suggest that species of electric rays with limited ranges in the tropical-subtropical southwestern Indian Ocean, particularly species of insular Torpedo and quite possibly narkid genera such as Electrolux and Heteronarce and species of narcinids (Narcine) are a major concern for conservation. The Ornate Sleeper Ray would be an appropriate subject for an intensive dive survey project by fish-watchers, professional ichthyologists and conservationists on the numerous dive sites of the northeast coast of the Eastern Cape, KwaZulu-Natal and Mozambique to attempt to better understand its distribution and estimate its abundance.
|Citation:||Compagno, L.J.V. 2009. Electrolux addisoni. The IUCN Red List of Threatened Species 2009: e.T161428A5421566. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161428A5421566.en . Downloaded on 04 October 2015.|
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