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, ONLF) |
North and west coast
(JANSF, ONLF, NCSF) |
Stock status |
|
|
|
Undefined |
Undefined |
Sustainable |
Indicators |
Catch |
Catch |
Catch, 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); JANSF = Joint Authority Northern Shark Fishery; NCSF = North Coast Shark Fishery (Western Australia); ONLF = Offshore Net and Line Fishery (Northern Territory); OTLF = Ocean Trap and Line Fishery (New South Wales)
Blacktip sharks, part of the family Carcharhinidae (whaler sharks), comprise 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 biological stock extending from the western Northern Territory into northern Western Australia, and an eastern biological stock extending from the Gulf of Carpentaria to the east coast of Queensland and New South Wales), three biological stocks of C. limbatus (one in Western Australia, 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. Currently, C. limbatus and C. tilstoni cannot be separately identified during fishing operations or in the field by scientists. C. sorrah has only recently been reported separately in commercial catches. Consequently, biological stocks are managed at the finest known scale - that is, the three biological stock areas identified above for C. limbatus - as a precautionary management measure.
East coast biological stocks
Insufficient information is available to determine status for any of the Blacktip Shark species in New South Wales2 or Queensland3. In 2009, Queensland introduced a precautionary quota of 600 tonnes (t) for all shark and ray species for the Queensland east coast; this is less than 50 per cent of the highest reported historical commercial catch, which occurred in 2003. However, there have not yet been any stock assessments by either New South Wales or Queensland. Queensland is three years into a five-year project of information collection and assessment for major commercial shark species, including the Blacktip Shark species complex, and expects to commence full stock assessments in 2013.
Until stock assessments are completed, the east coast biological stocks are classified as an undefined stock.
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 Queensland Gulf of Carpentaria Inshore Fin Fish Fishery from 2006, it has been difficult to determine the catches taken for stock assessment purposes. Consequently, the impact of current catch levels on this biological stock is unknown.
There is insufficient information to confidently classify the status of these biological stocks; therefore the Gulf of Carpentaria biological stocks are classified as an undefined stock.
North and west coast biological stocks
The north and west coast biological stock straddles two management jurisdictions: the Northern Territory, from the Wessel Islands to the Northern Territory – Western Australian border; and Western Australia.
The most recent assessments for these biological stocks estimated that the harvest rate for all Blacktip Shark species was well within sustainable limits, and current pup production is approximately 80 per cent of unfished levels4. Preliminary analysis of a mark–recapture study for C. tilstoni in the Northern Territory supports the stock assessment finding for this species. 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. The above evidence 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 north and west coast biological stocks are classified as a sustainable stock.
Table 2: Blacktip Shark biology5–7
Longevity and maximum size |
C. tilstoni: females 15 years, males 13 years; 200 cm
C. limbatus: maximum age unknown, 250 cm
C. sorrah: females 14 years, males 9 years; 160 cm |
Maturity (50%) |
C. tilstoni: 5–6 years; females 135–140 cm, males 120 cm
C. limbatus: males 180 cm, females unknown
C. sorrah: 2–3 years; both sexes 90–95 cm |
Figure 1: Distribution of reported commercial catch of Blacktip Shark in Australian waters, 2010
- Blacktip Sharks are caught by commercial fishers using monofilament gillnets and longline gear. Recreational fishers use rod and reel with bait. The east coast shark meshing (bather protection) programs use multifilament gillnets and baited large hooks (drum-lines) in Queensland.
- Blacktip Sharks are managed using a range of input and output controls:
- Input controls include limited entry to all commercial fisheries, spatial closures and gear restrictions.
- Output controls include total allowable catches and recreational size limits and bag limits.
- The number of vessels that caught Blacktip Sharks in 2010 was 0 in the Joint Authority Northern Shark Fishery, 0 in the North Coast Shark Fishery (Western Australia), 11 in the Offshore Net and Line Fishery (Northern Territory), 26 net and 13 line vessels in the East Coast Inshore Fin Fish Fishery (Queensland), 37 in the Gulf of Carpentaria Inshore Fin Fish Fishery (Queensland) and 106 in the Ocean Trap and Line Fishery (New South Wales).
- The total commercial Blacktip Shark catch in Australia in 2010 was 849 t, comprising 250 t (all from the Northern Territory) from the north and west coast biological stock, 434 t from the Gulf of Carpentaria biological stock, and 165 t from the east coast biological stock2–3,8–10.
Figure 2: Commercial catch of Blacktip Shark in Australian waters, 1992 to 2010 (calendar year)
Note: New South Wales, Queensland and Western Australian data are presented by financial year. 2010 refers to the 2010–11 financial year.
In New South Wales, only C. limbatus and C. tilstoni are caught in the Ocean Trap and Line Fishery2. Blacktip Shark catches have generally not exceeded 50 t per year, except for 2000–01, 2006–07 and 2007–08, when catches were 59.4 t, 100.7 t and 71.7 t, respectively (Figure 2). The annual recreational catch of whaler sharks in New South Wales is likely to range between 40 and 100 t, of which an unknown proportion is Blacktip Sharks. The Blacktip Shark catch in the New South Wales Shark Meshing Program in 2010 was five individuals, representing 3 per cent of the total number of individuals entangled11.
Catches of Blacktip Sharks in Queensland have been at or above 150 t since 2003, when more specific reporting was introduced (Figure 2). In the 2009–10 quota year, Blacktip Sharks comprised 38 per cent of the 501 t landed (of the 600 t total allowable commercial catch). On average, C. sorrah makes up only about 5 per cent of the total catch of the Blacktip Shark complex in Queensland east coast waters3.
For the Queensland part of the Gulf of Carpentaria Blacktip Shark catch, more species-specific logbook reporting for sharks was introduced in 2006 for Gulf net fishers. Data before this were not separated to species level. Catch in 2010 was 213 t, of which C. sorrah comprised around 10 per cent8.
In the Northern Territory, the Blacktip Shark catch increased from 272 t in 2001 to 469 t in 2010, with catches being stable and above 400 t since 2006 (Figure 2). In Western Australia, catches have generally been below 100 t over the past 20 years, although they peaked in 2001–02 and 2002–03 at 199 t and 208 t, respectively (Figure 2). Following the introduction of new management arrangements for the Joint Authority Northern Shark Fishery and the North Coast Shark Fishery in 2005, the mean annual Blacktip Shark catch was 67 t until 2009–10, when activity in these fisheries ceased9. There is no current harvest of Blacktip Sharks in Western Australia.
- Commercial gillnets and longline have almost no impact on marine habitat and are quite selective; bycatch makes up only a small proportion of the catch. 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 unknown3,8–10,12–13. Longline fishing on the east coast has been shown to have the potential to threaten the long-term viability of the east coast stock of Grey Nurse Shark14.
- The impact of environmental factors on Blacktip Shark biological stocks is unknown. However, 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