Australian blacktip shark

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Australian blacktip shark

Least Concern  (IUCN 3.1)[1]
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. tilstoni
Binomial name
Carcharhinus tilstoni
(Whitley, 1950)
Range of the Australian blacktip shark[2]
Synonyms

Galeolamna pleurotaenia tilstoni Whitley, 1950

The Australian blacktip shark (Carcharhinus tilstoni) is a

common blacktip shark (C. limbatus), from which it can be reliably distinguished only by its lower vertebra number and by genetic markers
. Generally reaching 1.5–1.8 m (4.9–5.9 ft) in length, it is a fairly stout-bodied, bronze-colored shark with a long snout and black-tipped fins.

Primarily

Least Concern
.

Taxonomy and phylogeny

The Australian blacktip shark was described by Australian

type specimen is a 1.5 m (4.9 ft) long female caught from Van Cloon Reef in Joseph Bonaparte Gulf.[3] Later authors have regarded Galeolamna as a synonym of the genus Carcharhinus. This shark may also be referred to as blacktip whaler, Tilston's whaler shark, and Whitley's blacktip shark.[4]

After Whitley's initial description, C. tilstoni was generally regarded as synonymous with C. limbatus, the

allozymes, mitochondrial DNA, and nuclear DNA have found that the Australian and common blacktip sharks form a closely related clade with the graceful shark (C. amblyrhynchoides) and the smoothtooth blacktip shark (C. leiodon).[6][7][8] The interrelationships between them have not been fully resolved, but available data suggest that C. tilstoni and C. limbatus are not the most closely related species within the clade despite their similarity.[7][9]

Description

The common blacktip shark (pictured) is nearly identical in appearance to the Australian blacktip shark.

Physically, the Australian blacktip shark can only reliably be distinguished from the common blacktip shark by the number of vertebrae (174–182 total, 84–91 before the tail in C. tilstoni, 182–203 total, 94–102 before the tail in C. limbatus). It has a moderately robust, spindle-shaped body and a long, pointed snout. The anterior rims of the nostrils are slightly enlarged into low triangular flaps. The large, circular eyes are equipped with nictitating membranes. The furrows at the corners of the mouth are barely evident. There are 32–35 upper and 29–31 lower tooth rows; each upper tooth has a slender, upright cusp and fine serrations that become coarser near the base, while the lower teeth are narrower and more finely serrated. The five pairs of gill slits are long.[9][10]

The long and narrow

dermal denticles are placed closely together and slightly overlapping; each bears five to seven (three in juveniles) horizontal ridges leading to marginal teeth. The Australian blacktip shark is bronze above (gray after death) and whitish below, with a pale stripe on the flanks. Some individuals have black tips on all fins, while others have unmarked pelvic and anal fins. It typically reaches 1.5–1.8 m (4.9–5.9 ft) long; the maximum length and weight on record are 2.0 m (6.6 ft) and 52 kg (115 lb).[9][10][11]

Distribution and habitat

Inhabiting the continental shelf, the Australian blacktip shark is found from Thevenard Island in Western Australia to Sydney in New South Wales.[2][10] Within its range, it co-occurs with the common blacktip shark; the ratio between C. limbatus and C. tilstoni was once thought to be 1:300, but recent genetic studies have found it to be closer to 50:50.[12] This species has been reported from the intertidal zone to a depth of 150 m (490 ft); larger sharks tend to occur in deeper water.[1] Though it occupies the entire water column, it is most common close to the surface or in midwater.[10] Genetic data suggest Australian blacktip sharks across northern Australia are all members of a single population.[13] Tagging studies have found this species mostly moves only short distances along the coastline and rarely enters offshore waters. However, some individuals have been recorded traveling longer distances, up to 1,348 km (838 mi).[14][15]

Biology and ecology

The longtail tuna is known to be preyed upon by the Australian blacktip shark.

The Australian blacktip shark is known to form large groups, segregated by size and sex.

tapeworms Fossobothrium perplexum[19] and Platybothrium sp.,[20] and the copepod Perissopus dentatus.[21]

Like other requiem sharks, the Australian blacktip shark is

maximum lifespan is estimated to be 20 years.[18][22]

cartilaginous fishes.[23]

Human interactions

Along with the spottail shark, the Australian blacktip shark is one of the most economically important sharks off northern Australia. It was historically fished for its meat and

gillnet fishery, which began operating off northern Australia in 1974. The annual catch initially averaged around 25,000 tons (live weight), with approximately 70% consisting of Australian blacktip sharks, spottail sharks, and longtail tuna (Thunnus tonggol). Following the establishment of the Australian Fishing Zone (AFZ) in November 1979, the Australian government progressively excluded Taiwanese gillnet vessels from large portions of Australian waters and imposed fishing quotas. The fishery eventually became uneconomical when Australia restricted gillnet lengths to 2.5 km (1.6 mi) in May 1986, and Taiwanese vessels ceased fishing in Australian waters that year.[15] At end of the fishery, Australian blacktip shark numbers were estimated to have been diminished by around 50%. Given its relatively high reproductive rate, its population has likely since recovered.[1]

Since 1980, the Australian blacktip shark has also been targeted by Australian commercial gillnetters and

Least Concern.[1] However, of potential concern are Indonesian fishers in the Arafura Sea, who are increasingly trespassing into the AFZ.[10][15]

References

  1. ^
    doi:10.2305/IUCN.UK.2019-1.RLTS.T41739A68613771.en
    . Retrieved 19 November 2021.
  2. ^
    PMID 21039498
    .
  3. ^ Whitley, G. P. (July 7, 1950). "A new shark from north-western Australia". Western Australian Naturalist. 2 (5): 100–105.
  4. ^ Froese, R.; Pauly, S.; eds. (2011). "Carcharhinus tilstoni" in FishBase. December 2011 version.
  5. S2CID 54989299
    .
  6. doi:10.1071/MF9920097
    .
  7. ^
    doi:10.1071/MF10159
    .
  8. PMID 21129490
    .
  9. ^
    ISBN 978-3-89937-132-1
    .
  10. ^
    ISBN 978-0-674-03411-2
    .
  11. ISBN 978-92-5-104052-2
    .
  12. S2CID 85574058
    .
  13. doi:10.1071/MF9890541
    .
  14. doi:10.1071/MF98158
    .
  15. ^
    ISBN 978-92-5-104291-5
    .
  16. doi:10.1071/MF9920087
    .
  17. ^
    S2CID 22998036
    .
  18. ^
    doi:10.1071/MF9860671
    .
  19. S2CID 3129825
    .
  20. S2CID 944343. Archived from the original
    (PDF) on April 24, 2012. Retrieved December 16, 2011.
  21. ^ Simpfendorfer, C.A. (1993). "Pandarid copepods parasitic on sharks from north Queensland waters". Memoirs of the Queensland Museum. 33 (1): 290.
  22. doi:10.1071/MF9880417
    .
  23. S2CID 14083730. Archived from the original
    (PDF) on 2014-03-22. Retrieved 2013-04-15.

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Australian_blacktip_shark&oldid=1185838891"