|Scientific Name:||Aetomylaeus bovinus (Geoffroy Saint-Hilaire, 1817)|
Myliobatis bovina Geoffroy Saint-Hilaire, 1817
Pteromylaeus bovina (Geoffroy Saint-Hilaire, 1817)
Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817)
|Taxonomic Source(s):||White, W.T. and Naylor, G.J.P. 2016. Resurrection of the family Aetobatidae (Myliobatiformes) for the pelagic eagle rays, genus Aetobatus. Zootaxa 4139(3): 435-438.|
|Taxonomic Notes:||White (2014) placed the genus Pteromylaeus Garman, 1913 into the synonymy of Aetomylaeus Garman, 1908.
This species is often confused with Myliobatus aquila.
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Reviewer(s):||Kyne, P.M., Fowler, S.L. & Compagno, L.J.V.|
This is an amended version of the 2006 assessment to accommodate Pteromylaeus being placed into synonym with Aetomylaeus.
A widespread species in the eastern Atlantic, including the Mediterranean, and the southwestern Indian, although the distribution is not completely and accurately defined. Little is known of the species' biology and ecology outside of South Africa where most of the information is historical (1940 to 1960s). In South Africa the species is taken as minor trawl bycatch and a minor bycatch of the KwaZulu-Natal shark protection nets (no significant trend in the catch rate of Natal Sharks Board (NSB) nets between 1977 and 2000). It is also caught by recreational fishers, but less frequently than other inshore elasmobranchs (e.g., Gymnura natalensis) and is generally released alive after capture. These low exploitation levels in South Africa as well as management considerations (reductions in NSB nets, reducing prawn trawl effort on the Tugela Bank, and recreational fishing restrictions) justify a Least Concern assessment for that country. However, given the historical nature of most ecological information, an update on the biology (maturity, litter size, nursery grounds etc.) and basic age and growth information is needed to reassess the regional status of this species in the near future. Elsewhere across its range, A. bovines is documented to be caught occasionally off Kenya and commonly off Senegal. Given the species' inshore occurrence, however, it is likely taken in coastal artisanal fisheries across much of its African range. Myliobatids are generally susceptible to a variety of inshore fishing gear and as such an assessment of catch levels across its range is a priority, particularly given the species' low fecundity (3 to 4 pups/litter) and the presence of generally unregulated and often intense fishing pressure on the inshore environment in some areas. At present, given the dearth of information on the species outside of South Africa, it is assessed globally as Data Deficient.
|Previously published Red List assessments:|
|Range Description:||The exact distribution of this species is uncertain and may be disjunct in the eastern Atlantic. While Fishbase.org lists the species as occurring in all countries of West Africa, its occurrence in many of these has not be conclusively verified and its complete distribution needs to be determined. It is however, confirmed from Morocco, Western Sahara, Senegal, Canary Islands, Madeira Islands, Mauritania, Gambia, Guinea and Guinea-Bissau (M. Ducrocq pers. comm. 06.09.03) and probably others. |
In southern Africa, A. bovinus is found from the southwestern Cape to Zanzibar and is apparently absent from cold waters off the western Cape coast and Namibia (Smith 1991). In Namibia it is possibly present only along the northern coast (absent in the cold upwelling waters) (Bianchi et al. 1999). Van der Elst (1988) provides the range as north of Saldhana Bay along the whole South African coast into Mozambique (as far as Maputo Bay Wallace (1967)). The species is also caught in Kenya (Ochumba 1988).
Native:Albania; Algeria; Angola; Benin; Bosnia and Herzegovina; Cameroon; Cape Verde; Congo; Côte d'Ivoire; Croatia; Cyprus; Egypt; Equatorial Guinea; France; Gabon; Gambia; Ghana; Gibraltar; Greece; Guinea; Guinea-Bissau; Israel; Italy; Kenya; Lebanon; Liberia; Libya; Malta; Mauritania; Monaco; Montenegro; Morocco; Mozambique; Namibia; Nigeria; Portugal (Madeira); Sao Tomé and Principe; Senegal; Sierra Leone; Slovenia; South Africa; Spain (Canary Is.); Syrian Arab Republic; Tanzania, United Republic of; Togo; Tunisia; Turkey; Western Sahara
|FAO Marine Fishing Areas:|
Atlantic – southeast; Atlantic – eastern central; Indian Ocean – western; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The population size and number, and the size of subpopulations, if any, are unknown.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Little information on habitat and ecology is available from outside South Africa and most of the following comes from that country (excepting some data from Senegal and Kenya):|
This tropical to warm-temperate species (Smith 1991) frequents coastal waters between the surf zone and 30 m (Van der Elst 1988) and down to 65m in the eastern Cape (Compagno et al. 1989). It tolerates greatly reduced salinities (Van der Elst 1988) and frequently enters estuaries and lagoons (Wallace 1967). It was regarded as common in the 1940 to 1960s (Wallace 1967, Smith 1991), but this needs to be re-examined.
P. bovines is not confined to the bottom, and is often seen on the surface (Van der Elst 1988), sometimes leaping from the water (Van der Elst 1988, Compagno et al. 1989, Smith 1991). It is sometimes found in small groups (Compagno et al. 1989). Between 1981 and 2001, Young (2001) found 26 occurrences of three or more bullrays caught in the same Natal Sharks Board (NSB) net installation in one or two days. Of those 10 were of mixed sex, seven comprised females only, five males only, and the rest were unknown. There was no distinct seasonal pattern, but most occurred in December, March and April.
The species is recorded throughout the year and is most common during summer months (Wallace 1967). Examining NSB net captures between 1981 and 2000, Young (2001) found that bullrays were caught throughout the year with peaks in November and December. Catch declined sharply in January then rose again in February and April. Minimum catches were observed in August and catches were generally lowest between July and September, with only 15.9% of the catch occurring during this period of the year. Significantly more males were caught during December-May, whereas the opposite was the case for females, which dominated catches in June-November. Bullray catch displayed a distinct pattern geographically related to the difference in water temperature with main catches in Richards Bay and Zinkwazi, as well as Winkelspruit and Park Rynie. Catches dropped dramatically south of Park Rynie. The sex ratio of NSB catches between 1981 and 2000 was 1:1.03 (m:f) (Young 2001).
Seck et al. 2002 found that in catches in Senegal, males were significantly more numerous than females and that females were significantly heavier than males. In their sample, both adult males and females were more abundant than juveniles. In KwaZulu-Natal, South Africa, Young (2001) examined NSB net captures between 1981 and 2000 and found that when using field length (FL, disc width), females were significantly bigger than males (median male: 81 cm FL, median female: 90 cm FL). The median for sexes combined was 83.4 cm (mode 70.1 to 80 cm FL, mean 87.7 cm FL). Lengths measured in the laboratory were generally larger than FL. The laboratory length mode was larger than FL at 100.1 to 110.0 cm. Female bullrays were larger than males, but not significantly so when using laboratory length (Young 2001).
Wallace (1967) examined 38 animals caught in the NSB nets ranging from 71.1 to 149.5 cm DW (2.72 to 56.2 kg) and three embryos (22 to 22.5 cm DW). He reported that males mature at 95 cm DW/13.6 kg and examined a gravid female of 119.4 cm DW/28.35 kg that contained three embryos (22 to 22.5 cm DW) in advanced development. Van der Elst (1988) gives a gestation period of one year after which 3 to 4 young are born, each at 50 cm DW. The smallest mature male dissected at the NSB was 104 cm DW and the smallest mature female was 105.5 cm DW (NSB, unpubl. data).
Off Senegal, Capapé et al. (1995) reports sexual maturity as 90 to 100 cm DW for females and 83 to 100 cm DW for males. Also off Senegal, Seck et al. (2002) found that adult males and females were over 82 cm DW and 90 cm DW, respectively. Eight fully developed fetuses ranged from 25 to 27 cm DW / 310 to 345 g. The smallest free-living specimen was 35.5 cm DW/460 g. Gestation lasted between five and six months. A block of oocytes appeared at the beginning of gestation and there was an inability to ovulate soon after parturition. Vitellogenesis recommenced when the embryos were practically at the end of their development. The reproductive cycle lasted one year at least. P. bovines is a pure matrotrophic species. Ovarian fecundity (6 to 8) is higher than uterine fecundity (3 to 4) and there was no relationship between size and both categories of fecundity.
According to the length-age curve of Van der Elst (1988), bullrays are ~14 years old at ~180 cm DW/100 kg. Using above local maturity lengths, both sexes mature at ~100 cm DW/10 kg, just over one year of age.
Smallest free-swimming individual: 71.1 cm DW (Wallace 1967); 35.5 cm DW/460 g (Seck et al. 2002); 30 cm NSB field length (25 cm dubious) (NSB, unpubl. data).
Largest observed embryos: 22.5 cm DW (Wallace 1967); 27 cm DW (Seck et al. 2002).
Maximum reported size: 175 cm DW (Smith 1991); 152 cm DW (Wallace 1976).
Largest observed animal: 149.5 cm DW (Wallace 1967); 115 cm DW/29.8 kg male, 148 cm DW/47.9 kg female (Seck et al. 2002); 190 cm DW (Ochumba 1988) (dubious?); 350 cm, 220 cm, 194 cm NSB field length (all dubious), 185 cm FL, 170 cm FL, 165 cm FL (78 kg) (NSB unpubl. data).
South Africa angling record: 100.2 kg.
Tagged by NSB between 1996 and 2002: 13 animals, no recaptures to date (NSB unpubl. data).
Tagged by shore anglers between 1984 and 2002: 594 animals, nine recaptures (1.01% recapture rate), which include washed up tags. Maximum distance moved: 34 km, maximum time at liberty: 1,427 days (Bullen et al. 2003).
Diet: crabs, hermit crabs, gastropod molluscs, mussels, bivalves, squid and prawns (Wallace 1967, Ochumba 1988, Compagno et al. 1989, Smith 1991).
Life history parameters
Age at maturity: ~1.2 years (male and female).
Size at maturity (disc width): 100 cm DW (male and female).
Longevity (years): Unknown.
Maximum size (disc width): 175 cm DW.
Size at birth: ~35 cm DW?
Average reproductive age (years): Unknown.
Gestation time: 5 to 6 months (Senegal); 12 months (Southern Africa).
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: Litter size: 3 to 4.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Wallace (1967) reported that this species is seine netted in Durban and Richards Bay, South Africa. Fennessy (1994) reported that a small number (just six in a three year period) are taken by prawn trawlers operating on the Tugela Bank. The species is also sometimes caught by offshore trawlers (Compagno et al. 1989) and more recent data from prawn trawlers operating on the Tugela Bank again showed low levels of bycatch in that fishery: one animal in 46 trawls in September 2002 and six animals in 46 trawls in April/May 2003 (MCM, unpubl. data).
The species is caught by shore anglers (Van der Elst 1988, Smith 1991) but due to identification problems (species often confused with M. aquila) it is difficult to obtain accurate angling catch figures. Pradervand and Govender (2003) examined the competitive shore angling catch in the border region (Great Fish river - Kei river) between 1982 and 1998 and combined A. bovinus and Myliobatis aquila. They found that during the study period 531 animals (2.7% of the total catch, total mass 4,020.8 kg) were caught. Pradervand (2004), again combining the two species, reported 58 animals (0.3% of total catch, 419.5 kg) being caught between 1977 and 2000 during Natal Coast Anglers Union's angling competitions in the former Transkei. Although most anglers prefer to return bullrays to the water alive (Van der Elst 1988, S. Wintner pers. obs.), release mortality is unknown and could be substantial due to the angling practices of gaffing, weighing etc. (S. Wintner pers. obs). It is interesting to note that the recapture rate of A. bovinus tagged in the South African National Tagging program is only 0.57% (Bullen et al. 2003).
Between 1981 and 2000, 798 animals (11.31% of total batoid catch), consisting mainly of juveniles, were caught in the NSB nets (Young 2001). Mean annual catch was 39.9 and mean catch rate was 0.98 (no animals/km net/yr). During the study period there was considerable variation in catch rate (0.47-1.78) and no significant trend was apparent. There was, however, a significant increasing trend in size caught. Mortality levels were moderate (44.2%, mean = 17.65 animals per year) and there was no significant trend in mortality over the time period. The highest catches occurred at Richards Bay, Zinkwazi and Durban, the highest catch rates were observed at Zinkwazi, Winkelspruit and Park Rynie. Overall, it is difficult to determine the impact of NSB nets on the population, but it is likely to be localized, as this species is not exploited anywhere else to a great extend (Young 2001).
Little information is available on catches outside of South Africa, but given the species' inshore occurrence it is likely taken in coastal artisanal fisheries across much of its range. It is known to be caught in small numbers in Kenya. Nine specimens (71-190 cm DW, 4.0-20.5 kg) were taken from commercial trawlers and local fishermen during a two year survey period (Ochumba 1988). The species is also commonly caught off the coast of Senegal (Seck et al. 2002), and as mentioned above, likely in other parts of its distribution.
Habitat degradation where human pressure on the coastal zone is high (i.e., through development, pollution etc.) is another threat likely affecting this species. Activities on the coastal zone and adjacent waterfront may impact upon important nursery area habitat.
Artisanal fisheries operating in west and east Africa are generally unregulated and attempts to monitor and regulate fisheries in these regions would greatly improve conservation of this and other chondrichthyans. Fishery-independent surveys of this and other elasmobranchs are necessary to provide estimates of abundance and biomass.
In addition to species-specific catch details, further ecological information (including age, growth, longevity, movement patterns, habitat use, potential nursery areas, diet, reproductive studies) is required. Direct estimates of fishing and natural mortality are critical for assessing fisheries impacts on a particular species. Tagging, tracking, and genetic studies are essential for determining the population structure, movement patterns, and possible subpopulations throughout the species' range.
A recent reduction in the number of protective shark nets off KwaZulu-Natal, South Africa will help to limit catches in that region. The recreational line fishery in South Africa is managed by a bag limit of one/species/person/day for unspecified chondrichthyans, which includes A. bovinus. Effort in the Tugela Bank fishery has been decreasing and as of May 2004, only three operators remain in the fishery.
The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. See Anon. (2004) for an update of progress made by nations in the range of A. bovinus.
|Citation:||Wintner, S. 2016. Aetomylaeus bovinus. The IUCN Red List of Threatened Species 2016: e.T60127A104022824.Downloaded on 23 October 2017.|
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