Marine turtles
Australian waters are home to six of the world’s seven species of marine turtle. These species are all protected under the EPBC Act and listed under the Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention for the Conservation of Migratory Species (CMS). Five of the species found within eastern Australian waters are also listed as endangered and critically endangered under the International Union for the Conservation of Nature’s (IUCN) Red List 2011 (IUCN, 2011). A marine turtle may take up to 30–50 years to mature (Marine Species Section, 2003), making them extremely vulnerable to impacts on population size.
It is stated within the Federal Recovery Plan for Marine Turtles in Australia (Marine Species Section, 2003) that "Marine turtles are vulnerable to boat strikes when at the surface to breathe and rest between dives. This is particularly an issue in waters adjacent to large urban populations (Limpus & Reimer, 1994) where there are large numbers of boats and other pleasure craft... The marine turtle populations affected by boat strike have been identified as: loggerhead turtles from the eastern Australian population; green turtles from the southern Great Barrier Reef population; hawksbill turtles from the north-eastern Australian populations; and flatback turtles from Queensland." Records illustrate the olive ridley turtle to be victim to boat strike on occasion (e.g. Haines & Limpus, 2001). Furthermore, boat strike is regularly mentioned in a review of impacts ‘of greatest relevance to turtle populations in the World Heritage Area’ of the Great Barrier Reef (Dobbs, 2001).
Australia is home to some of the largest nesting sites of the green, loggerhead and hawksbill turtles in the Indo-Pacific region, and the only nesting sites of the flatback turtle (Marine Species Section, 2003). A summary of the numbers of turtles known to have been killed by boat strike in Queensland between 1998 and 2002 is presented in Table 3, with data being obtained from the Queensland Department of Environment and Resource Management (DERM) Marine Wildlife Stranding and Mortality Database Annual Reports.
Table 3: Marine turtle mortalities cause by boat strike in Queensland waters between 1999-2004
Species
|
1999
|
2000
|
2001
|
2002
|
2003
|
2004
|
Total
|
Chelonia mydas
|
69
|
57
|
66
|
55
|
48
|
65
|
360
|
Caretta caretta
|
8
|
10
|
8
|
5
|
3
|
5
|
39
|
Dermochelys coriacea
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
Eretmochelys imbricata
|
0
|
3
|
1
|
1
|
0
|
0
|
5
|
Lepidochelys olivacea
|
3
|
3
|
0
|
0
|
0
|
1
|
7
|
Natator depressus
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
Total
|
80
|
73
|
75
|
61
|
53
|
71
|
413
|
From 1998-2002, confirmed boat strike accidents accounted for an average of 80 annual turtle mortalities along the Queensland shoreline alone, although this is probably an underestimation since cause of death could not be determined in 57% of cases, plus we can assume many carcasses are not discovered. The majority of those killed were green turtles. Boat strikes have proven to be one of the leading causes of turtle fatality from human-induced causes. Between 1999 and 2002 an annual average of 36.8% of all sea turtle mortalities in which cause of death could be determined (15% of all strandings and mortalities) within Queensland waters were due to boat strikes, with injuries consistent with propeller damage and fractures (Table 4).
Table 4: Records of documented turtles mortalities for Queensland waters from 1998-2002 showing the percentage of confirmed mortalities attributed to boat strike
Year
|
Total number of dead or stranded marine turtles
|
Number for which cause of mortality could be determined
|
Number of turtles killed due to anthropomorphic causes
|
Number attributed to boat strike
|
% of confirmed deaths due to boat strike
|
1999
|
554
|
195
|
150
|
84
|
56.0*
|
2000
|
495
|
172
|
130
|
78
|
60.0*
|
2001
|
529
|
168
|
139
|
83
|
59.7*
|
2002
|
526
|
172
|
149
|
65
|
43.6*
|
2003
|
527
|
140
|
117
|
60
|
51.3*
|
2004
|
574
|
173
|
156
|
75
|
48.1*
|
Total
|
3,205
|
1,020
|
841
|
445
|
52.9*
|
* = boat strike caused more than or as many deaths than any other anthropogenic activity recorded
It is worth noting that were cause of mortality proportions to remain consistent throughout the marine turtle strandings which were unconfirmed or had an unidentifiable cause of death, the number that would be attributable to boat strike (currently 445/1,020) would rise to approximately 1,400 individuals. Even this figure, focusing only on mortality on the Queensland coastline, is likely to represent only a fraction of actual mortality rates due to many instances going undetected or unreported. When considering this, it is clear that boat strike is a key threatening process to EPBC Act listed marine turtles in Australia.
The impact of boat strike on turtles is recognised in the Marine Turtle Recovery Plan (2003) as being particularly significant in the Moreton Bay and Harvey Bay areas. The Recovery Plan aims to increase turtle populations in the wild by reducing human induced mortality. Incidence of boat strike on marine turtles is of significance not only in Moreton Bay and Harvey Bay, but also in the Hinchinbrook area which is of increasing concern due to marine traffic and consequent injuries to turtles increase with increasing development (Limpus et al., 2002).
The impact of boat strike on green and loggerhead turtle populations is most evident through the data outlined in Table 3, and these species will be focused on in more depth later in this nomination. This will also be the case with the leatherback turtle, which warrants closer scrutiny due to its conservation status as Critically Endangered internationally (IUCN, 2011) and listing under all State / Territory with coastline (ACT being the only exception) threatened species legislation.
Flatback (Natator depressus), olive-ridley (Lepidochelys olivacea), and hawksbill (Eretmochelys imbricata) turtles are recognised as threatened Federally under the EPBC Act, Internationally through CMS, IUCN and CITES, and under various State / Territory laws. They are uncommon in the Great Barrier Reef region and data is correspondingly lacking in DERM’s Marine Wildlife Stranding and Mortality Database Annual Reports, thus little data is available regarding cause of mortality. However, these Annual Reports, the most recent of which is Greenland et al. (2006), show that between 1999-2004 one flatback, five hawksbill, and seven olive ridley turtles were recorded as stranded or killed by boat strike on the Queensland coast. Thus, even though data that fulfils the criteria for inclusion in the KTP is not comprehensive, it should be considered that three additional rare turtles in Australian waters are affected by this process, and may be more severely in other areas throughout their Australian range where they are more common.
Green turtle (Chelonia mydas)
Australian conservation status:
National: Listed as Vulnerable, Marine and Migratory species under the Environment Protection and Biodiversity Conservation Act, 1999.
New South Wales: Listed as Vulnerable under the Threatened Species Conservation Act, 1995.
Queensland: Listed as Vulnerable under the Nature Conservation Act, 1992.
Western Australia: Listed as Vulnerable under the Wildlife Conservation Act, 1950
International conservation status:
-
Listed on Appendix I of the Convention of International Trade in Endangered Species of Fauna and Flora (CITES).
-
Listed as Endangered on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species.
-
Listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
According to Queensland Government’s Marine Wildlife Stranding and Mortality Database Annual Reports (see Table 3), green turtles account for approximately 87.2% of boat strike mortalities to marine turtles in Queensland. Annual mortality rates attributable to boat strikes surpass mortality rates from any other cause, including all natural causes combined and such anthropogenic impacts as shark net entanglement and traditional hunting.
Of the total confirmed green turtle mortalities where the cause of death could be determined contained within the Marine Wildlife Stranding and Mortality Database Annual Reports, greater than 50% (360/705) featured fractures and injuries consistent with boat strike and propeller damage (Table 5). Comparatively, only 15.2% of cause of death confirmed stranding and mortalities were due to natural causes such as disease and depredation, a figure which indicates the severe stress boat strike incidents are placing on non-impacted green turtle population dynamics.
Table 5: Records of reported green turtle mortalities in Queensland waters from 1998-2002 showing the percentage of confirmed mortalities attributed to boat strike
Year
|
1999
|
2000
|
2001
|
2002
|
2003
|
2004
|
Total
|
Total confirmed mortality
|
134
|
108
|
125
|
118
|
108
|
112
|
705
|
Natural causes
|
26
|
22
|
20
|
20
|
16
|
3
|
107
|
Anthropogenic
|
108
|
86
|
105
|
98
|
92
|
109
|
598
|
Boat Strike
|
69
|
57
|
66
|
55
|
48
|
65
|
360
|
% anthro. boatstrike
|
63.9*
|
66.3*
|
62.9*
|
56.1*
|
52.2*
|
59.6*
|
60.2
|
* = boat strike caused more than or as many deaths than any other anthropogenic activity recorded
It is worth noting that boat strike was the leading confirmed cause of mortality of reported incidents on the Queensland coast in all of the six years for which data was collected, significantly higher than any other factor. It is stated within Hazel et al. (2007) that “Individual green turtles are known to maintain long-term fidelity to their coastal foraging areas, with only brief absences during breeding migrations spaced several years apart (Limpus et al. 1992, 1994). Thus, for each individual turtle in a foraging area that receives vessel traffic, the risk of collision persists over decades”. This behavioural trait may be a significant factor in why instances of boat strike on green turtles are so common.
The severity of the threat of boat strike to green turtles is rivalled only by that of Indigenous traditional hunting. It is however a threat that is relatively straightforward to abate compared to the indigenous use. If the threat of boat strike were to continue the species will continue to decline. Together with the loggerhead turtle (below), it meets the KTP listing criterion that the threatening process adversely affects an EPBC Act listed species.
Loggerhead turtle (Caretta caretta)
Australian conservation status:
National: Listed as Endangered, Marine and Migratory species under the Environment Protection and Biodiversity Conservation Act, 1999.
New South Wales: Listed as Endangered under the Threatened Species Conservation Act, 1995.
Northern Territory: Listed as Endangered under the Territory Parks and Wildlife Conservation Act, 2001.
Queensland: Listed as Endangered under the Nature Conservation Act, 1992.
Western Australia: Listed as Rare or likely to become extinct under the Wildlife Conservation Act, 1950
International conservation status:
-
Listed on Appendix I & II of the Convention of International Trade in Endangered Species of Fauna and Flora (CITES).
-
Listed as Endangered on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species.
-
Listed on Appendix I of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
It has been acknowledged at many levels of government that the loggerhead turtle, Caretta caretta, is under significant threat. The species is recognised under the EPBC Act as an Endangered species, acknowledging the fact that if the species’ survival remains threatened, it may become extinct, and the recovery of the population of loggerhead turtles in Queensland is threatened most significantly by boat strike (see Table 6). Loggerhead mortality as a result of boat strike appears to be increasing, which means that boat strike has the capacity to endanger the recovery of this reduced population (XXXX XXXX pers. comm.).
The loggerhead turtle is a relatively long-lived animal, with a life expectancy of at least 50 years and sexual maturity reached at between 8 and 15 years, with non-annual, periodic egg-production (NSW Scientific Committee, 2001).
During the last two decades, loggerhead populations have been decreasing faster than any other marine turtle species, and it has lost up to 80% of its nesting population on the east coast (Parish, 2001).
Population models were developed using long-term mark-recapture data from loggerhead turtles feeding in the Heron Island region. These models indicate that small declines in annual survival rates of adult and sub-adult loggerheads can have an extreme impact on population dynamics. It is predicted that a loss of a few hundred loggerhead turtles can lead to the extinction of the eastern Australia population within a century (Heppell et al., 1996).
Anthropogenic effects and disturbances on loggerhead population growth are difficult to measure due to the large time frame taken for maturity in this and other turtle species. There is therefore a lag time between the cause and effect of declining population numbers. For this reason, immediate and drastic action must be taken to significantly reduce mortality by means of anthropogenic causes, in particular boat striking. This also demonstrates that the precautionary approach must be used here.
The Department of Environment and Resource Management of the Queensland Government compiles ongoing stranding and mortality databases for marine wildlife. From 1998 until 2004, boat strike was the principal anthropogenic cause of stranding and mortality of loggerheads in Queensland (Table 6), with the Annual Reports indicating that the annual mortality rates due to boat strikes (total of 39 between 1999-2004) out-number mortality rates from all natural causes combined (5) significantly. Of the total confirmed loggerhead turtle mortalities where the cause of death could be determined contained within the Marine Wildlife Stranding and Mortality Database Annual Reports, approximately 35.8% (39/109) featured fractures and injuries consistent with boat strike and propeller damage (Table 6). Comparatively, only 22.9% of cause of death confirmed stranding and mortalities were due to natural causes such as disease and depredation, a figure which, as was the case with the green turtle, indicates the severe stress boat strike incidents are placing on non-impacted green turtle population dynamics.
Table 6: Records of reported loggerhead turtle mortalities in Queensland waters from 1998-2002 showing the percentage of confirmed mortalities attributed to boat strike
Year
|
1999
|
2000
|
2001
|
2002
|
2003
|
2004
|
Total
|
Total confirmed mortality
|
28
|
27
|
17
|
12
|
12
|
13
|
109
|
Natural causes
|
6
|
9
|
3
|
0
|
5
|
2
|
25
|
Anthropogenic
|
22
|
18
|
14
|
12
|
7
|
11
|
84
|
Boat Strike
|
8
|
10
|
8
|
5
|
3
|
5
|
39
|
% anthro. boatstrike
|
36.4*
|
55.6*
|
57.1*
|
41.7*
|
42.9*
|
45.5*
|
46.4
|
* = boat strike caused more than or as many deaths than any other anthropogenic activity recorded
It is therefore clear that this threat is adversely affecting this EPBC Act listed species, as it threatens the recovery of the species from its severe status of decline that resulted from years of being caught in trawling nets. The listing of ‘Fatal injury to marine mammals, reptiles, and other large marine species through boat strike on the Australian coast’ as a Key Threatening Process and development of a Threat Abatement Plan are essential to avoid the recovery of the species being compromised.
Leatherback turtle (Dermochelys coriacea)
Australian conservation status:
National: Listed as Endangered, Marine and Migratory species under the Environment Protection and Biodiversity Conservation Act, 1999.
New South Wales: Listed as Endangered under the Threatened Species Conservation Act, 1995.
Northern Territory: Listed as Endangered under the Territory Parks and Wildlife Conservation Act, 2001.
Queensland: Listed as Endangered under the Nature Conservation Act, 1992.
South Australia: Listed as Vulnerable under National Parks and Wildlife Act, 1972.
Tasmania: Listed as Vulnerable under Threatened Species Protection Act, 1995.
Victoria: Listed as Threatened under the Flora and Fauna Guarantee Act, 1988.
Western Australia: Listed as Rare or likely to become extinct under the Wildlife Conservation Act, 1950
International conservation status:
-
Listed on Appendix I of the Convention of International Trade in Endangered Species of Fauna and Flora (CITES).
-
Listed as Critically Endangered on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species.
-
Listed on Appendix I & II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
Boat strike is relatively (when compared to green and loggerhead turtles) uncommon for leatherback turtles, with data from the Queensland Department of Environment and Resource Management’s Stranding and Mortality Database Annual Reports listing just one instance of leatherback boat strike mortality between 1999-2004 (Table 7). However, this low figure for boat strike for this species reflects its rarity in Australia, and it should be noted that only four mortalities from any cause were recorded in the databases – boat strike effectively being the cause of 25% of known cause mortality. Although this number appears very low, to a population reported to be in danger of extinction within less than 10 years (Science Daily, 2004) it is still a dangerous number of unnecessary deaths which, as was the case with previously mentioned species, is likely highly understated due to unreported or undetected incidents.
Table 7: Records of reported leatherback turtle mortalities in Queensland waters from 1998-2002 showing the percentage of confirmed mortalities attributed to boat strike
Year
|
1999
|
2000
|
2001
|
2002
|
2003
|
2004
|
Total
|
Total confirmed mortality
|
1
|
1
|
0
|
0
|
1
|
1
|
4
|
Natural causes
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
Anthropogenic
|
1
|
1
|
0
|
0
|
1
|
1
|
4
|
Boat Strike
|
0
|
0
|
0
|
0
|
1
|
0
|
1
|
% anthro. boatstrike
|
0.0
|
0.0
|
0.0
|
0.0
|
100.0*
|
0.0
|
25.0
|
* = boat strike caused more than or as many deaths than any other anthropogenic activity recorded
Other species affected by boat strike which may not meet EPBC Act criteria
Although the species described below may not meet the prescribed criteria for inclusion as part of the Key Threatening Process due to limited data being accessible to the nominator, they are included here in an attempt to provide a more complete picture of the impact of boat strike on marine wildlife.
Humpback whale (Megaptera novaeangliae)
Australian conservation status:
National: Listed as Vulnerable, Cetacean and Migratory species under the Environment Protection and Biodiversity Conservation Act, 1999.
New South Wales: Listed as Vulnerable under the Threatened Species Conservation Act, 1995.
Queensland: Listed as Vulnerable under the Nature Conservation (Wildlife) Regulation, 2006.
South Australia: Listed as Vulnerable under the National Parks and Wildlife Act, 1972.
Tasmania: Listed as Endangered under the Threatened Species Protection Act, 1995.
Victoria: Listed as Threatened under the Flora and Fauna Guarantee Act, 1988.
Western Australia: Listed as Rare or likely to become extinct under the Wildlife Conservation Act, 1950
International conservation status:
-
Listed on Appendix I of the Convention of International Trade in Endangered Species of Fauna and Flora (CITES).
-
Listed on Appendix I of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
It is likely that many ship strikes on whale species go undetected or unreported as they may occur in remote areas, the impact may not be detected, animals may be struck and passed over without being observed, or struck whales may drift out to sea, thus the actual number of strikes is undoubtedly greater than confirmed data shows (Jensen & Silber, 2004). According to Jensen & Silber (2004), humpback whales are the second most impacted upon whale species by boat strike throughout the world (with finback whales having the highest boat strike mortality count), with 44 being recorded as boat strike mortalities from the earliest record in 1885 up to 2002, with entries being highly varied chronilogically throughout that range.
As a characteristically coastal species of whale (Jensen & Silber, 2004), humpbacks are likely at greater risk of boat strike in areas of higher boat use than other migratory Australian species. In Australia, there is an east and a west coast population of migratory humpback whales that are considered to be genetically distinct (Baker et al., 1998), and there are records of humpback whales that have been found stranded and killed in Queensland (Greenland et al., 2005). Although confirmed cases with cause attributed to boatstrike are few and far between, to a small population of long-lived and large animals this still represents a threat. Furthermore, boat strikes on humpback whales are likely to increase if the humpback population continues to recover on the east coast and as boat traffic increases.
Whale shark (Rhincodon typus)
Australian conservation status:
National: Listed as Vulnerable and Migratory species under the Environment Protection and Biodiversity Conservation Act, 1999.
South Australia: Listed as Vulnerable under the National Parks and Wildlife Act, 1972.
Tasmania: Listed on the Fisheries (General and Fees) Regulations, 2006 under the Living Marine Resources Management Act, 1995.
Western Australia: Listed as a totally protected fish under the Conservation and Land Management Act, 1984 and the Fish Resources Management Act, 1994.
International conservation status:
-
Listed on Appendix II of the Convention of International Trade in Endangered Species of Fauna and Flora (CITES).
-
Listed as Vulnerable on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species.
-
Listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).
-
Listed on Annex I (Highly Migratory Species) of the United Nations Convention on the Law of the Sea (UNCLOS).
Rodger et al. (2010) states that whale sharks are vulnerable to boat strikes, with individuals observed to actively approach boats, possibly being attracted to bubbles created by idling engines. Stevens (2007) goes as far as saying that whale shark mortality related to human activity (other than fishing) occurs mainly through boat strikes.
Whale sharks spend a lot of time close to the surface, resulting in an increased chance of incidences of boat strikes, evidenced by a typical scarring pattern on the animals (Norman, 1999; Mau, 2006; Stevens, 2007). The incidence of fin damage and scarring on whale sharks observed during ecotourism activities, so common that such markings are used along with natural colouration to identify whale sharks through computer algorithms (Arzoumanian et al., 2005), suggests that non-fatal collisions, probably with smaller vessels, are not uncommon (Stevens, 2007). It is thought this may have further adverse impacts on the species, by resulting in whale sharks showing a higher level of boat avoidance behaviours, including the avoidance of areas which may be critical habitats (Mau, 2006).
According to Stevens (2007), Gudger (1940) documented many instances of collisions between whale sharks and large vessels and there have been several reports of whale sharks impaled on the bows of steamships earlier this century (Stead, 1963). With regard to modern shipping, large vessels are probably not aware of striking whale sharks, leading to the extent of such mortality to be unknown (Norman, 1999). The rarity of beached whale shark specimens, which would allow increased analysis of whale shark mortality and cause of mortality in Australian waters, suggest that R. typus tends to sink rapidly after death (Tubb, 1948).
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