Pigeye shark

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Pigeye shark
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Carcharhinus
Species:
C. amboinensis
Binomial name
Carcharhinus amboinensis
(Müller & Henle, 1839)
Range of the pigeye shark[2]
Synonyms

Carcharias amboinensis Müller & Henle, 1839
Carcharias henlei Bleeker, 1853
Carcharias brachyrhynchos Bleeker, 1859
Triaenodon obtusus Day, 1878

The pigeye shark or Java shark (Carcharhinus amboinensis) is an uncommon species of requiem shark, in the family Carcharhinidae, found in the warm coastal waters of the eastern Atlantic and western Indo-Pacific. It prefers shallow, murky environments with soft bottoms, and tends to roam within a fairly localised area. With its bulky grey body, small eyes, and short, blunt snout, the pigeye shark looks almost identical to (and is often confused with) the better-known bull shark (C. leucas). The two species differ in vertebral count, the relative sizes of the dorsal fins, and other subtle traits. This shark typically reaches lengths of 1.9–2.5 m (6.2–8.2 ft).

The pigeye shark is an

fisheries, which use it for meat and fins. The IUCN
presently assesses this species as vulnerable.

Taxonomy

Drawing of Triaenodon obtusus, a synonym of C. amboinensis, from Francis Day's Fauna of British India (1889)

German biologists

foetus.[4]

Phylogeny and evolution

Since the pigeye shark so strongly resembles the bull shark,

molecular phylogenetic research, which to date has been inconclusive regarding this shark's evolutionary relationship to other Carcharhinus species.[7][8]

Genetic analysis of pigeye sharks across northern Australia suggest that the evolutionary history of this species was affected by coastline changes during the

epoch (2.6 million to 12,000 years ago). The patterns of diversity found in its mitochondrial DNA are consistent with the repeated splitting and merging of its populations as geographical barriers were alternately formed and inundated. The most recent of these barriers was a land bridge across the Torres Strait that reopened only some 6,000 years ago; as a result, significant genetic separation exists between the sharks found off Western Australia and the Northern Territory and those found off Queensland.[9]

Description

The pigeye shark (top) closely resembles the bull shark (bottom); external differences between the two species include the relative sizes of the dorsal fins and the angle of the notch in the anal fin.

The pigeye shark is a very robust-bodied species with a short, broad, and rounded snout. The small and circular eyes are equipped with

tooth rows on each side; in addition, there are single rows of tiny teeth at the upper and lower symphyses (jaw midpoints). The teeth are broad and triangular with serrated edges; those in the lower jaw are slightly narrower, more upright, and more finely serrated than those in the upper. The five pairs of gill slits are of moderate length.[2][4][10]

The first

caudal fin origin. The caudal fin is asymmetrical, with a well-developed lower lobe and a longer upper lobe with a notch in the trailing margin near its tip.[2][4][10]

The skin is covered by rather large

albino individual was caught off Queensland in 1987, which was the first known example of albinism in a requiem shark.[11] An adult pigeye shark typically measures 1.9–2.5 m (6.2–8.2 ft) long, while the largest individuals reach 2.8 m (9.2 ft) long.[2]

The pigeye shark can be most reliably distinguished from the bull shark by the number of precaudal (before the caudal fin) vertebrae (89–95 in C. amboinensis versus 101–123 in C. leucas). Externally, it has a greater size difference between its dorsal fins (first-to-second height ratio >3.1:1 versus ≤3.1:1 in C. leucas) and the notch in its anal fin margin forms an acute angle (versus a right angle in C. leucas). This species also usually has fewer tooth rows in the lower jaw (10–12 on each side versus 12–13 in C. leucas).[2][4]

Distribution and habitat

Though widely distributed in the

subtropical marine waters of Eurasia, Africa, and Oceania, the pigeye shark does not appear to be common anywhere. Existing records are patchy, and the full extent of its range may be obscured by confusion with the bull shark.[1] In the eastern Atlantic, it is found off Cape Verde and Senegal, and from Nigeria to Namibia;[2] there is a single Mediterranean record from off Crotone, Italy.[12] It occurs all along the continental periphery of the Indian Ocean, from eastern South Africa to the Arabian Peninsula (including Madagascar, the Seychelles, and Mauritius), to Southeast Asia and northern Australia. Its range extends into the Pacific, northward to the Philippines and southern China, and eastward to New Guinea and some Micronesian islands.[2] Tagging and genetic data indicate that pigeye sharks, particularly juveniles, are not strongly migratory and tend to remain in a local area. The longest recorded distance covered by an adult is 1,080 km (670 mi).[9][10]

The pigeye shark inhabits coastal waters down to a depth of 150 m (490 ft), favouring environments with fine

dissolved oxygen levels.[14][15]

Biology and ecology

The pigeye shark is a largely solitary animal, though occasionally several individuals may be found at the same location.

tapeworms Callitetrarhynchus gracilis,[18] Cathetocephalus sp.,[19] Floriceps minacanthus,[20] Heteronybelinia australis,[21] Otobothrium australe, O. crenacolle,[22] and Protogrillotia sp.[18] Young pigeye sharks are potentially vulnerable to predation by larger sharks. The natural mortality for juveniles in Cleveland Bay has been measured at no more than 5% per year; this rate is comparable to that in juvenile bull sharks, and is much lower than in juvenile blacktip sharks (C. limbatus) or lemon sharks (Negaprion brevirostris).[23]

Feeding

Guitarfishes and other cartilaginous fishes are preyed upon by the pigeye shark, particularly off South Africa.

Though the pigeye shark will take prey from anywhere in the

angel sharks, guitarfishes, stingrays, and eagle rays.[13]

Life history

The pigeye shark is

gestation period lasts about 12 months, with mating and birthing both occurring in late summer. The litters range from three to seven pups (average five) and the newborns are around 75–79 cm (30–31 in) long.[1][13] Off northern Australia, the gestation period lasts 9 months, with birthing taking place in November and December. The litters range from six to 13 pups (average 9) and the newborns are around 59–66 cm (23–26 in) long.[25]

Young sharks can be found in shallow

maximum lifespan is at least 26 years for males and 30 years for females.[25][28]

Human interactions

Large and formidably toothed, the pigeye shark is regarded as potentially dangerous to humans, though it has not been implicated in any attacks. This species is caught infrequently on

Near Threatened in the southwestern Indian Ocean.[1]

References

  1. ^
    doi:10.2305/IUCN.UK.2021-2.RLTS.T39366A173434051.en. Retrieved 19 November 2021.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  2. ^
    ISBN 978-3-89937-132-1
    .
  3. ^ Müller, J.; Henle, F.G.J. (1839). Systematische Beschreibung der Plagiostomen. Vol. 2. Veit und Comp. p. 40.
  4. ^
    ISBN 978-92-5-101384-7
    .
  5. ISBN 978-0-691-08453-4
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  6. S2CID 39697113
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  7. PMID 21129490
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  8. ISBN 978-1-4398-3924-9
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  9. ^
    S2CID 15426537
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  10. ^
    ISBN 978-0-674-03411-2
    .
  11. ^ McKay, R.J.; Beinssen, K. (1988). "Albinism in the pigeye whaler shark Carcharhinus amboinensis Mueller and Henle from Queensland Australia". Memoirs of the Queensland Museum. 25 (2): 463–464.
  12. ^ De Maddalena, A.; Della Rovere, G. (2005). "First record of the pigeye shark, Carcharhinus amboinensis (Müller & Henle, 1839), in the Mediterranean Sea" (PDF). Annales Series Historia Naturalis. 15 (2): 209–212.
  13. ^
    doi:10.2989/025776191784287817
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  14. ^
    doi:10.3354/meps09006
    .
  15. doi:10.1071/MF10136
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  16. S2CID 25023218
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  17. doi:10.1017/S1755267213000195
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  18. ^
    PMID 19761769
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  19. PMID 16019004
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  20. ^ Campbell, R.A.; Beveridge, I. (1987). "Floriceps minacanthus sp. nov. (Cestoda: Trypanorhyncha) from Australian fishes" (PDF). Transactions of the Royal Society of South Australia. 111 (3–4): 189–194. Archived from the original (PDF) on 2014-12-15.
  21. ^ Palm, H.W.; Beveridge, I. (2002). "Tentaculariid cestodes of the order Trypanorhyncha (Platyhelminthes) from the Australian region". Records of the South Australian Museum. 35 (1): 49–78.
  22. S2CID 18892377
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  23. doi:10.1016/j.fishres.2012.02.023
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  24. doi:10.3354/meps09327
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  25. ^
    doi:10.1071/MF9910151
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  26. doi:10.1016/j.biocon.2012.01.008
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  27. doi:10.3354/meps09222
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  28. doi:10.1071/MF10271
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  29. PMID 7725322
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External links

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