Australian Blacktip Shark (Carcharhinus tilstoni)
Table 1: Stock status determination for Blacktip Shark
Jurisdiction |
New South Wales, Queensland |
Northern Territory, Queensland |
Northern Territory, Western Australia |
Stock |
East coast
(ECIFFF, OTLF) |
Gulf of Carpentaria
(GOCIFFF, GOCLF, ONLF) |
North and west coast
(JANSF, KGBF, NCSF, ONLF) |
Stock status |
|
|
|
Undefined |
Undefined |
Sustainable |
Indicators |
Catch |
Catch |
Catch, mark recapture, CPUE, pup production |
CPUE = catch per unit effort; ECIFFF = East Coast Inshore Fin Fish Fishery (Queensland); GOCIFFF = Gulf of Carpentaria Inshore Fin Fish Fishery (Queensland); GOCLF = Gulf of Carpentaria Line Fishery (Queensland); JANSF = Joint Authority Northern Shark Fishery (Western Australia); KGBF = Kimberley Gillnet and Barramundi Fishery (Western Australia); NCSF = North Coast Shark Fishery (Western Australia); ONLF = Offshore Net and Line Fishery (Northern Territory); OTLF = Ocean Trap and Line Fishery (New South Wales)
In the context of Australian fisheries, the Blacktip Shark species complex, part of the family Carcharhinidae (whaler sharks), comprises three species: Carcharhinus tilstoni, C. limbatus and C. sorrah. Whereas C. tilstoni and C. sorrah are distributed within Australian and Indo–West Pacific waters, respectively, C. limbatus is globally distributed in tropical and warm temperate waters. In Australian waters, genetic studies have identified two biological stocks of C. tilstoni (a western stock extending from the western Northern Territory into northern Western Australia, and an eastern stock extending from the Gulf of Carpentaria to the east coast of Queensland and New South Wales), three biological stocks of C. limbatus (one across Western Australia and the Northern Territory, one in the Gulf of Carpentaria, and one on the east coast of Queensland and New South Wales) and a single biological stock of C. sorrah across northern Australia1. Specific stock boundaries between the western biological stocks of C. tilstoni and C. limbatus and those in the Gulf of Carpentaria are uncertain.
Currently, commercially caught size classes of C. limbatus and C. tilstoni can only be taxonomically differentiated by genetic analyses or precaudal vertebral counts (although recent evidence of these species’ hybridisation may affect the accuracy of these techniques2,3 ). Thus, reliable species differentiation is not practical during fishing operations. Although C. sorrah can be clearly distinguished from C. tilstoni and C. limbatus, it has only relatively recently been reported separately in commercial catch records from Northern Territory, Queensland and Western Australian fisheries. Because a suite of three species is grouped together for this assessment, all with differing stock structures, stocks have been assessed on the finest known scale—that is, the three biological stock areas identified for C. limbatus.
East coast biological stocks
Blacktip Shark species are an important component of shark fisheries in New South Wales4 and Queensland5. In 2009, Queensland introduced a precautionary annual quota of 600 tonnes (t) for all shark and ray species (combined) for the Queensland east coast. This is less than 50 per cent of the highest reported historical annual commercial catch, which occurred in 2003. Although there have not yet been any stock assessments by either New South Wales or Queensland, genetic analysis techniques are currently being used to estimate the effective population size for the east coast stock of C. limbatus. Queensland is currently undertaking a stock assessment for major commercial shark species, including the Blacktip Shark species complex, and expects results to be available in late 2014. Until this assessment is complete, stock status cannot be assigned to these biological stocks.
On the basis of the evidence provided above, the biological stocks are classified as undefined stocks.
Gulf of Carpentaria biological stocks
Substantial Blacktip Shark catches are harvested from the Gulf of Carpentaria. However, since species identification of sharks has only been undertaken in the Gulf of Carpentaria Inshore Fin Fish Fishery (Queensland) from 2006, it has been difficult to obtain enough data specific to catches of Blacktip Sharks for stock assessment purposes. Consequently, the impact of current catch levels on these biological stocks is unknown, and there is insufficient information to confidently classify their status.
On the basis of the evidence provided above, the biological stocks are classified as undefined stocks.
North and west coast biological stocks
The north and west coast biological stocks straddle two management jurisdictions: the Northern Territory, west of the Wessel Islands – Western Australian border; and Western Australia.
The most recent assessment for these biological stocks estimated that the harvest rates for all species within the complex are currently well within sustainable limits, and current pup production is approximately 80 per cent of unfished levels6. A mark–recapture study in the Northern Territory for all species of Blacktip Sharks supports the stock assessment results7.
Although there is uncertainty in the species composition and magnitude of historical Blacktip Shark catches from Western Australia, these species are not currently harvested in this jurisdiction. Evidence from both jurisdictions indicates that the biomass of this biological stock is unlikely to be recruitment overfished and that current catch levels are unlikely to cause the biological stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stocks are classified as sustainable stocks.
Table 2: Blacktip Shark biology2,8-10
Longevity and maximum size |
C. tilstoni: females 15 years, males 13 years; 2000 mm TLa
C. limbatus: maximum age unknown, 2500 mm TLa
C. sorrah: females 14 years, males 9 years; 1600 mm TL |
Maturity (50%) |
C. tilstoni: 5–6 years; females 1350–1400 mm, males 1200 mm TLa
C. limbatus: males 1800 mm, females unknowna
C. sorrah: 2–3 years; both sexes 900–950 mm TL |
TL = total length
a These biological estimates do not account for hybridisation between C. tilstoni and C. limbatus.
Figure 1: Distribution of reported commercial catch of Blacktip Sharks in Australian waters, 2013 (calendar year)
Table 3: Main features and statistics for Blacktip Shark fisheries in Australia, 2013 (calendar year)5,11–15
Jurisdiction |
Northern Territory |
Western Australia |
Queensland |
New South Wales |
Fishing methods |
Commercial |
Pelagic gillnet |
✓ |
|
✓ |
|
Demersal gillnet |
|
✓ |
✓ |
✓ |
Anchored longline |
✓ |
|
|
✓ |
Recreational |
Rod and line |
✓ |
✓ |
✓ |
✓ |
Hand line |
|
✓ |
|
|
Indigenousa |
Hand line |
✓ |
Unknown |
✓ |
|
Spearfishing |
✓ |
Unknown |
|
|
Management methods |
Commercial |
Limited entry |
✓ |
|
✓ |
✓ |
Vessel restrictions |
✓ |
|
✓ |
✓ |
Total allowable effort |
✓ |
|
|
✓ |
Total allowable catch |
|
|
✓ |
|
Spatial closures |
✓ |
✓ |
|
✓ |
Gear restrictions |
✓ |
✓ |
✓ |
✓ |
Commercial protection |
|
✓ |
|
|
Recreational |
Licences |
|
✓ |
|
✓ |
Bag limits |
|
✓ |
✓ |
✓ |
Possession limits |
✓ |
|
|
|
Size limits |
|
|
✓ |
|
Gear restrictions |
✓ |
✓ |
✓ |
✓ |
Spatial closures |
✓ |
✓ |
✓ |
✓ |
Charter |
Licences |
✓ |
✓ |
✓ |
✓ |
Bag limits |
|
✓ |
✓ |
✓ |
Possession limits |
✓ |
|
|
|
Size limits |
|
|
✓ |
|
Gear restrictions |
✓ |
✓ |
✓ |
|
Spatial closures |
✓ |
✓ |
✓ |
✓ |
Indigenousa,b |
No limits on customary catch |
✓ |
✓ |
|
✓ |
Active vessels |
|
7 in ONLF |
0 in JANSF
1 in KGBF
0 in NCSF |
78 in ECIFFF
27 in GOCIFFF
1 in GOCLF |
52 in OTLF |
Catch |
Commercial |
111 t in ONLF
|
0 t in JANSF
0.1 t in KGBF
0 in NCSF |
144 t in ECIFFF
184 t in GOCIFFF
0.1 t in GOCLF |
3.6 t in OTLF |
Recreational |
Unknown |
Unknown |
Unknown |
Unknown |
Charter |
Unknown |
Unknown |
Unknown |
Unknown |
Indigenous |
Unknown |
Unknown |
Unknown |
Unknown |
Markets |
Domestic |
✓ |
n/a |
✓ |
✓ |
Export |
✓ |
n/a |
✓ |
✓ |
ECIFFF = East Coast Inshore Fin Fish Fishery; GOCIFF = Gulf of Carpentaria Inshore Fin Fish Fishery (Queensland); GOCLF = Gulf of Carpentaria Line Fishery (Queensland); JANSF = Joint Authority Northern Shark Fishery (Western Australia); KGBF = Kimberley Gillnet and Barramundi Fishery (Western Australia); n/a = not available; NCSF = North Coast Shark Fishery (Western Australia); ONLF = Offshore Net and Line Fishery (Northern Territory); OTLF = Ocean Trap and Line Fishery (New South Wales)
a In Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers in Queensland are able to use prescribed traditional and noncommercial fishing apparatus in waters open to fishing. Size and possession limits, and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.
b Subject to the defence that applies under section 211. of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by indigenous fishers is covered by the same arrangements as that for recreational fishing.
Figure 2: Commercial catch of Blacktip Sharks in Australian waters, 1999 to 2013 (calendar years)
Pelagic gillnets and longlines are not intended to come into contact with the seabed, and, under normal circumstances, they have no impact on benthic habitats. Demersal gillnets contact the seabed but are generally set away from any benthic structures (for example, reefs, sponges or mangroves) that could be damaged by them, or cause damage to them. The physical characteristics of these gears and the way in which they are fished are also selective for the target species and size classes.
However, these fishing methods do interact with threatened, endangered and protected (TEP) species. Although reported interactions are low, the impact on the populations of most TEP species is either unknown5,12–14,16,17 or assessed as negligible to low12. Longline fishing on the east coast has been shown to have the potential to threaten the long-term viability of the east coast population of Grey Nurse Shark (Carcharias taurus)18.
- The impact of environmental factors on biological stocks of Blacktip Shark is unknown. These species are adapted to a range of environmental conditions and are therefore likely to be resilient to environmental changes.
a Department of Primary Industry and Fisheries, Northern Territory
b Department of Fisheries, Western Australia
c Department of Primary Industries, New South Wales
d Department of Agriculture, Fisheries and Forestry, Queensland