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Kirby Smith - One of the best experts on this subject based on the ideXlab platform.
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does the grey Nurse Shark carcharias taurus exhibit agonistic pectoral fin depression a stereo video photogrammetric assessment off eastern australia
Pacific Conservation Biology, 2016Co-Authors: Kirby Smith, Carol Scarpaci, Brett M Louden, Nicholas M OtwayAbstract:Underwater stereo-video photogrammetry was used to document the pectoral fin positions of various life-history stages of the critically endangered east Australian population of the grey Nurse Shark (Carcharias taurus) during normal swimming behaviour at multiple aggregation sites. A wide range in pectoral fin positions was recorded with dihedral pectoral fin angles ranging from –25 to 88°. Pectoral fin angles varied significantly among sites and this was attributed to the differing navigational and energetic requirements of the Sharks. There was no significant relationship between pectoral fin angles and distances separating the Shark and scuba diver. The wide range in pectoral fin angles, interactive use of the fins during swimming, low-energy behaviours of the Sharks at aggregation sites and absence of ‘fight’ response agonistic behaviour indicated that the species does not exhibit agonistic pectoral fin depression. Reports of agonistic pectoral fin depression in the grey Nurse Shark obtained with visual estimates should be treated as preliminary observations requiring further testing using accurate sampling methods such as stereo photogrammetry. It is important that diver compliance with existing management guidelines that prohibit divers from chasing or harassing grey Nurse Sharks and blocking cave and gutter entrances is maintained.
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Behavioural ecology of the critically endangered grey Nurse Shark (Carcharias taurus) and the interaction with scuba diving tourism off eastern Australia
2016Co-Authors: Kirby SmithAbstract:The critically endangered grey Nurse Shark (Carcharias taurus) off eastern Australia is the focus of a non-consumptive, economically important marine wildlife tourism (MWT) industry centred on scuba diving with the Sharks. This industry has been identified as a potential threat to the continued survival and recovery of the species. Legislative guidelines and a national code of conduct for scuba diver behaviour were developed to mitigate adverse impacts of MWT on the Sharks. This research assessed the putative impacts of scuba diving MWT on grey Nurse Shark behaviour and the efficacy of management strategies across differing life-history stages and aggregation sites. Underwater stereo-video photogrammetry was used to develop a partial ethogram of the swimming and non-swimming behaviours of grey Nurse Sharks at locations within aggregation sites during daylight hours without MWT. Predominantly low-energy behaviours were exhibited and no threatening agonistic behaviours were observed. Underwater visual census also documented primarily low-activity swimming behaviours in Sharks during interactions with MWT scuba divers of varying demographics and revealed absolute diver compliance with management guidelines. Passive acoustic telemetry showed Sharks may have exhibited more active swimming when patrolling between two locations within a site but adopted low-energy swimming behaviours for the majority of the time during daylight hours regardless of scuba diving MWT. Sharks at differing life-history stages probably conserved energy at aggregation sites in association with their migratory movements and reproductive cycles. Differences in the swimming and patrolling behaviours of Sharks were attributed to natural variation in environmental conditions (i.e. topography and currents) at the sites as they were not consistent with scuba diving MWT activity. This research strongly suggested that management strategies are effective at protecting the east Australian population of grey Nurse Sharks from MWT disturbance. Consequently, the grey Nurse Shark scuba diving MWT industry in its current form is ecologically and economically sustainable.
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Grey Nurse Shark (Carcharias taurus) Diving Tourism: Tourist Compliance and Shark Behaviour at Fish Rock, Australia
Environmental Management, 2010Co-Authors: Kirby Smith, Mark Scarr, Carol ScarpaciAbstract:Humans can dive with critically endangered grey Nurse Sharks ( Carcharias taurus ) along the east coast of Australia. This study investigated both compliance of tourist divers to a code of conduct and legislation and the behaviour of grey Nurse Sharks in the presence of divers. A total of 25 data collection dives were conducted from December 2008 to January 2009. Grey Nurse Shark and diver behaviour were documented using 2-min scan samples and continuous observation. The proportion of time spent observing human–Shark interactions was 9.4% of total field time and mean human–Shark interaction time was 15.0 min. Results were used to gauge the effectiveness of current management practices for the grey Nurse Shark dive industry at Fish Rock in New South Wales, Australia. Grey Nurse Shark dive tourists were compliant to stipulations in the code of conduct and legislation (compliance ranged from 88 to 100%). The research detailed factors that may promote compliance in wildlife tourism operations such as the clarity of the stipulations, locality of the target species and diver perceptions of Sharks. Results indicated that grey Nurse Sharks spent the majority of their time milling (85%) followed by active swimming (15%). Milling behaviour significantly decreased in the presence of more than six divers. Distance between Sharks and divers, interaction time and number of Sharks were not significantly correlated with grey Nurse Shark school behaviour. Jaw gaping, rapid withdrawal and stiff or jerky movement were the specific behaviours of grey Nurse Sharks that occurred most frequently and were associated with distance between divers and Sharks and the presence of six or more divers. Revision of the number of divers allowed per interaction with a school of grey Nurse Sharks and further research on the potential impacts that Shark-diving tourism may pose to grey Nurse Sharks is recommended.
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does grey Nurse Shark carcharias taurus diving tourism promote biocentric values within participants
2009Co-Authors: Kirby Smith, Mark J Scarr, Carol ScarpaciAbstract:In Australia, humans can dive with critically endangered grey Nurse Sharks (Carcharias taurus) at Fish Rock, New South Wales. This industry has the potential to improve the environmental knowledge of participants and encourage pro-environmental attitudes within tourists. This study surveyed tourists pre and post participation in grey Nurse Shark dives to ascertain if the experience positively influenced the grey Nurse Shark knowledge and biocentric attitudes of tourists (short-term). Educational talks were provided to tourists of alternating boat trips to assess if education had a significant impact upon the knowledge and biocentrism of these tourists compared with those that were not provided with a talk. Survey data were collected across eight grey Nurse Shark dive boat trips from December 2008 to January 2009. Results indicated that those individuals likely to participate in a grey Nurse Shark dive were generally already knowledgeable and biocentric, hence the scope for further improvement was quite narrow. Significant improvements to the grey Nurse Shark knowledge and biocentric attitudes of tourists post dive were detected, however the majority of these improvements occurred within tourists already considered to be highly biocentric and knowledgeable pre dive experience. The provision of educational talks significantly improved the knowledge of participants but not their biocentrism. These findings are of importance as they highlight that the contribution the industry may provide to conservation by improving the biocentric attitudes and environmental knowledge of tourists may be minimal. Furthermore, it is important that accurate educational resources are developed and provided to tourists pre and post dive to avoid the development of misconceptions by tourists during grey Nurse Shark dives.
Carol Scarpaci - One of the best experts on this subject based on the ideXlab platform.
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does the grey Nurse Shark carcharias taurus exhibit agonistic pectoral fin depression a stereo video photogrammetric assessment off eastern australia
Pacific Conservation Biology, 2016Co-Authors: Kirby Smith, Carol Scarpaci, Brett M Louden, Nicholas M OtwayAbstract:Underwater stereo-video photogrammetry was used to document the pectoral fin positions of various life-history stages of the critically endangered east Australian population of the grey Nurse Shark (Carcharias taurus) during normal swimming behaviour at multiple aggregation sites. A wide range in pectoral fin positions was recorded with dihedral pectoral fin angles ranging from –25 to 88°. Pectoral fin angles varied significantly among sites and this was attributed to the differing navigational and energetic requirements of the Sharks. There was no significant relationship between pectoral fin angles and distances separating the Shark and scuba diver. The wide range in pectoral fin angles, interactive use of the fins during swimming, low-energy behaviours of the Sharks at aggregation sites and absence of ‘fight’ response agonistic behaviour indicated that the species does not exhibit agonistic pectoral fin depression. Reports of agonistic pectoral fin depression in the grey Nurse Shark obtained with visual estimates should be treated as preliminary observations requiring further testing using accurate sampling methods such as stereo photogrammetry. It is important that diver compliance with existing management guidelines that prohibit divers from chasing or harassing grey Nurse Sharks and blocking cave and gutter entrances is maintained.
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Grey Nurse Shark (Carcharias taurus) Diving Tourism: Tourist Compliance and Shark Behaviour at Fish Rock, Australia
Environmental Management, 2010Co-Authors: Kirby Smith, Mark Scarr, Carol ScarpaciAbstract:Humans can dive with critically endangered grey Nurse Sharks ( Carcharias taurus ) along the east coast of Australia. This study investigated both compliance of tourist divers to a code of conduct and legislation and the behaviour of grey Nurse Sharks in the presence of divers. A total of 25 data collection dives were conducted from December 2008 to January 2009. Grey Nurse Shark and diver behaviour were documented using 2-min scan samples and continuous observation. The proportion of time spent observing human–Shark interactions was 9.4% of total field time and mean human–Shark interaction time was 15.0 min. Results were used to gauge the effectiveness of current management practices for the grey Nurse Shark dive industry at Fish Rock in New South Wales, Australia. Grey Nurse Shark dive tourists were compliant to stipulations in the code of conduct and legislation (compliance ranged from 88 to 100%). The research detailed factors that may promote compliance in wildlife tourism operations such as the clarity of the stipulations, locality of the target species and diver perceptions of Sharks. Results indicated that grey Nurse Sharks spent the majority of their time milling (85%) followed by active swimming (15%). Milling behaviour significantly decreased in the presence of more than six divers. Distance between Sharks and divers, interaction time and number of Sharks were not significantly correlated with grey Nurse Shark school behaviour. Jaw gaping, rapid withdrawal and stiff or jerky movement were the specific behaviours of grey Nurse Sharks that occurred most frequently and were associated with distance between divers and Sharks and the presence of six or more divers. Revision of the number of divers allowed per interaction with a school of grey Nurse Sharks and further research on the potential impacts that Shark-diving tourism may pose to grey Nurse Sharks is recommended.
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does grey Nurse Shark carcharias taurus diving tourism promote biocentric values within participants
2009Co-Authors: Kirby Smith, Mark J Scarr, Carol ScarpaciAbstract:In Australia, humans can dive with critically endangered grey Nurse Sharks (Carcharias taurus) at Fish Rock, New South Wales. This industry has the potential to improve the environmental knowledge of participants and encourage pro-environmental attitudes within tourists. This study surveyed tourists pre and post participation in grey Nurse Shark dives to ascertain if the experience positively influenced the grey Nurse Shark knowledge and biocentric attitudes of tourists (short-term). Educational talks were provided to tourists of alternating boat trips to assess if education had a significant impact upon the knowledge and biocentrism of these tourists compared with those that were not provided with a talk. Survey data were collected across eight grey Nurse Shark dive boat trips from December 2008 to January 2009. Results indicated that those individuals likely to participate in a grey Nurse Shark dive were generally already knowledgeable and biocentric, hence the scope for further improvement was quite narrow. Significant improvements to the grey Nurse Shark knowledge and biocentric attitudes of tourists post dive were detected, however the majority of these improvements occurred within tourists already considered to be highly biocentric and knowledgeable pre dive experience. The provision of educational talks significantly improved the knowledge of participants but not their biocentrism. These findings are of importance as they highlight that the contribution the industry may provide to conservation by improving the biocentric attitudes and environmental knowledge of tourists may be minimal. Furthermore, it is important that accurate educational resources are developed and provided to tourists pre and post dive to avoid the development of misconceptions by tourists during grey Nurse Shark dives.
Robert Harcourt - One of the best experts on this subject based on the ideXlab platform.
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Conservation of the Critically Endangered Eastern Australian Population of the Grey Nurse Shark (Carcharias taurus) Through Cross-Jurisdictional Management of a Network of Marine-Protected Areas
Environmental Management, 2013Co-Authors: Tim P. Lynch, Robert Harcourt, Graham Edgar, Neville BarrettAbstract:Between 2001 and 2009, 26 marine-protected areas (MPA) were established on the east Australian seaboard, at least in part, to manage human interactions with a critically endangered population of grey Nurse Shark, Carcharias taurus. This network is spread across six MPA systems and includes all 19 sites outlined in the National Recovery Plan for C. taurus , though five sites remain open to some forms of fishing. The reserve network has complex cross-jurisdictional management, as the Sharks occur in waters controlled by the Australian states of New South Wales (NSW) and Queensland, as well as by the Commonwealth (Federal) government. Jurisdiction is further complicated by fisheries and conservation departments both engaging in management activities within each state. This has resulted in protected area types that include IUCN category II equivalent zones in NSW, Queensland, and Commonwealth marine parks that either overlay or complement another large scaled network of protected sites called critical habitats . Across the network, seven and eight rule permutations for diving and fishing, respectively, are applied to this population of Sharks. Besides sites identified by the recovery plan, additional sites have been protected as part of the general development of MPA networks. A case study at one of these sites, which historically was known to be occupied by C. taurus but had been abandoned, appears to shows re-establishment of an aggregation of juvenile and sub-adult Sharks. Concurrent with the re-establishment of the aggregation, a local dive operator increased seasonal dive visitation rates at the site fourfold. As a precautionary measure, protection of abandoned sites, which includes Nursery and gestating female habitats are options that may assist recovery of the east coast population of C. taurus .
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Nuclear and mitochondrial DNA reveals isolation of imperilled grey Nurse Shark populations (Carcharias taurus).
Molecular ecology, 2009Co-Authors: Heidi Ahonen, Robert Harcourt, Adam J. StowAbstract:Loss of Sharks and other upper-trophic marine predators has sparked worldwide concern for the stability of ocean ecosystems. The grey Nurse (ragged-tooth or sand tiger) Shark (Carcharias taurus) is Vulnerable on a global scale, Critically Endangered in Australia and presumed extinct in parts of its historical range. We used 193 muscle and fin samples collected from six extant populations to assess global mtDNA and microsatellite diversity and the degree of global population genetic structure. Control region mtDNA diversity was low in every population, and two populations (eastern Australia and Japan) contained only a single mtDNA haplotype. Genetic signatures of recent losses of genetic variation were not yet apparent at microsatellite loci, indicating that this low mtDNA variation is not a result of anthropogenic population declines. Population differentiation was substantial between each population pair except Brazil and South Africa, FST values ranged from 0.050 to 0.699 and 0.100 to 1.00 for microsatellite and mitochondrial data respectively. Bayesian analysis clearly partitioned individuals into five of the populations from which they were sampled. Our data imply a low frequency of immigrant exchange among each of these regions and we suggest that each be recognized as a distinct evolutionary significant unit. In contrast to pelagic species such as whale Shark and white Shark that may cross ocean basins and where cooperative international efforts are necessary for conservation, grey Nurse Shark, like many coastal species, need to be managed regionally.
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estimating the rate of quasi extinction of the australian grey Nurse Shark carcharias taurus population using deterministic age and stage classified models
Biological Conservation, 2004Co-Authors: Nicholas M Otway, Corey J A Bradshaw, Robert HarcourtAbstract:Abstract Grey Nurse Sharks off the east coast of Australia are listed nationally as “critically endangered” under Schedule 1 of the Environmental Protection and Biodiversity Conservation Act (1999) and may number no more than 300 in New South Wales and southern Queensland waters. They are an inshore, coastal dwelling species and were severely depleted by spearfishing in the 1960s. The population has continued to decline despite protection since 1984. Their life history (long-lived to 25+ years), late maturation (6–8 years), low fecundity (maximum 2 live young biennially), specific habitat requirements, limited inshore distribution, and small population size render them particularly vulnerable to extinction. We estimated the time to quasi-extinction (years elapsed for the population to consist of ⩽50 females) for the grey Nurse Shark population off the east coast of Australia based on current estimates of abundance and known anthropogenic rates of mortality. Estimated minimum population size was 300 as of 2002, and minimum anthropogenic mortality assessed from recovered carcasses was 12/year of which 75% were females. We modelled time to quasi-extinction using deterministic age- and stage-classified models for worst-, likely and best-case scenarios. Population size was estimated at 300 (worst), 1000 (likely) and 3000 (best). Anthropogenic mortality was added to the model assuming either all carcasses are being recovered (best), or conservatively, that only 50% are reported (realistic). Depending on model structure, if all carcasses are being reported, quasi-extinction times for worst-, likely and best-case scenarios range from 13 to 16 years, 84–98 years and 289–324 years, respectively. If under-reporting is occurring, time to quasi-extinction ranges from 6 to 8 years, 45–53 years and 173–200 years, respectively. In all scenarios modelled the grey Nurse Shark population will decline if no further steps are taken to remove anthropogenic sources of mortality. Because estimates of quasi-extinction rate depend on initial population size, and sensitivity analysis revealed that population rate of change was most sensitive to changes in the survival probability of the smallest length classes, obtaining precise estimates of abundance and annual survival of young females is critical.
Jane E Williamson - One of the best experts on this subject based on the ideXlab platform.
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hook shaped enterolith and secondary cachexia in a free living grey Nurse Shark carcharias taurus rafinesque 1810
Veterinary Medicine and Science, 2021Co-Authors: Nicholas M Otway, Greg West, Damian B Gore, Jane E WilliamsonAbstract:The carcass of a critically endangered, juvenile female grey Nurse Shark (Carcharias taurus, Rafinesque 1810) was recovered from a south-eastern Australian beach and subjected to necropsy. The 1.98-m-long Shark exhibited advanced cachexia with its total weight (19.0 kg) and liver weight (0.37 kg) reduced by 60% and 89%, respectively, compared with a healthy individual of the same length. Marked tissue decomposition was evident preventing histopathology and identification of a definitive cause of death. At necropsy, the abdominal organs were abnormally displaced and showed marked reductions in size compared with a healthy individual of the same size. Importantly, a hook-shaped enterolith (HSE), with a rough surface and cream in colour, was found within the spiral valve of the intestine and is to the authors' knowledge, the first description of such in any marine animal. X-ray diffractometry showed that the HSE comprised the minerals monohydrocalcite (Ca[CO₃].H₂O; ~70 wt%) and struvite (Mg [NH4 ] [PO4 ]. [H2 O]6 ; ~30 wt%). A CT scan showed concentric lamellate concretions around a 7/o offset J-hook that formed the nidus of the HSE. Nylon fishing line attached to the hook exited the HSE and was evident in the abdominal cavity through a perforation in the intestinal wall where the posterior intestinal artery merges. The most parsimonious reconstruction of events leading to enterolithiasis and secondary cachexia in this Shark was the consumption of a hooked fish and subsequent hook migration causing perforations of the cardiac stomach wall followed by the thin, muscular wall of the apposed, sub-adjacent intestine.
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a video and photographic study of aggregation swimming and respiratory behaviour changes in the grey Nurse Shark carcharias taurus in response to the presence of scuba divers
Marine and Freshwater Behaviour and Physiology, 2011Co-Authors: Sean M. Barker, Victor M. Peddemors, Jane E WilliamsonAbstract:The Grey Nurse Shark (Carcharias taurus) is a popular attraction for Shark eco-tourism using SCUBA. The species is also ‘globally Vulnerable’ (IUCN 2008. List of Threatened Species. www.iucnredlist.org/). Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these Sharks. The objective of this study was to experimentally test the level of the activities of recreational SCUBA divers on Shark behaviour. This study assessed the Shark responses to diver group size (4, 8 and 12), time of day (am, noon and pm) and diver distance from the Sharks (3 m and 6 m). The study found that diver activity does affect the aggregation, swimming and respiratory behaviour of Sharks at this site, albeit at short-term levels. Diver group size had no significant effect on Shark aggregation, but the proximity of divers to the Sharks was crucial. Shark distribution in the cave changed significantly in the presence of divers at 3 m distance from the cave, but stayed unchanged at 6 m. This ...
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Recreational SCUBA diver interactions with the critically endangered Grey Nurse Shark Carcharias taurus
Pacific Conservation Biology, 2010Co-Authors: Sean M. Barker, Victor M. Peddemors, Jane E WilliamsonAbstract:Grey Nurse Sharks Carcharias taurus are listed as 'Critically Endangered' along the east coast of Australia. Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these Sharks. This study was conducted to answer the question: do current recreational SCUBA diving practices at Magic Point have a significant impact on the aggregation behaviour of C. taurus? The study found that diver activity does temporarily affect the behaviour of C. taurus at this site, with a significant difference in the number of Sharks and their distribution within the preferred area of occupation inside the cave between diver and non-diver treatments. Small dive groups (less-than-or-equal-to 4 divers) approached the cave closer than large groups, resulting in a greater impact on Sharks than large groups positioned further back from the cave. Shark behaviour rapidly returned to pre-diver exposure levels once divers left the area. This study is the first to (a) monitor recreational SCUBA diver activities at a critical habitat site and (b) use a noninvasive behavioural technique to study the behavioural responses of C. taurus towards SCUBA divers in southern NSW. It contributes to improving C. taurus conservation measures along the east coast of Australia by highlighting current diver behaviour and its impact on Grey Nurse Sharks at this site. Results suggest that changes in the current code of practice regarding SCUBA diving at recognized and protected Grey Nurse Shark critical habitat sites should be considered by relevant management agencies.
Nicholas M Otway - One of the best experts on this subject based on the ideXlab platform.
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hook shaped enterolith and secondary cachexia in a free living grey Nurse Shark carcharias taurus rafinesque 1810
Veterinary Medicine and Science, 2021Co-Authors: Nicholas M Otway, Greg West, Damian B Gore, Jane E WilliamsonAbstract:The carcass of a critically endangered, juvenile female grey Nurse Shark (Carcharias taurus, Rafinesque 1810) was recovered from a south-eastern Australian beach and subjected to necropsy. The 1.98-m-long Shark exhibited advanced cachexia with its total weight (19.0 kg) and liver weight (0.37 kg) reduced by 60% and 89%, respectively, compared with a healthy individual of the same length. Marked tissue decomposition was evident preventing histopathology and identification of a definitive cause of death. At necropsy, the abdominal organs were abnormally displaced and showed marked reductions in size compared with a healthy individual of the same size. Importantly, a hook-shaped enterolith (HSE), with a rough surface and cream in colour, was found within the spiral valve of the intestine and is to the authors' knowledge, the first description of such in any marine animal. X-ray diffractometry showed that the HSE comprised the minerals monohydrocalcite (Ca[CO₃].H₂O; ~70 wt%) and struvite (Mg [NH4 ] [PO4 ]. [H2 O]6 ; ~30 wt%). A CT scan showed concentric lamellate concretions around a 7/o offset J-hook that formed the nidus of the HSE. Nylon fishing line attached to the hook exited the HSE and was evident in the abdominal cavity through a perforation in the intestinal wall where the posterior intestinal artery merges. The most parsimonious reconstruction of events leading to enterolithiasis and secondary cachexia in this Shark was the consumption of a hooked fish and subsequent hook migration causing perforations of the cardiac stomach wall followed by the thin, muscular wall of the apposed, sub-adjacent intestine.
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does the grey Nurse Shark carcharias taurus exhibit agonistic pectoral fin depression a stereo video photogrammetric assessment off eastern australia
Pacific Conservation Biology, 2016Co-Authors: Kirby Smith, Carol Scarpaci, Brett M Louden, Nicholas M OtwayAbstract:Underwater stereo-video photogrammetry was used to document the pectoral fin positions of various life-history stages of the critically endangered east Australian population of the grey Nurse Shark (Carcharias taurus) during normal swimming behaviour at multiple aggregation sites. A wide range in pectoral fin positions was recorded with dihedral pectoral fin angles ranging from –25 to 88°. Pectoral fin angles varied significantly among sites and this was attributed to the differing navigational and energetic requirements of the Sharks. There was no significant relationship between pectoral fin angles and distances separating the Shark and scuba diver. The wide range in pectoral fin angles, interactive use of the fins during swimming, low-energy behaviours of the Sharks at aggregation sites and absence of ‘fight’ response agonistic behaviour indicated that the species does not exhibit agonistic pectoral fin depression. Reports of agonistic pectoral fin depression in the grey Nurse Shark obtained with visual estimates should be treated as preliminary observations requiring further testing using accurate sampling methods such as stereo photogrammetry. It is important that diver compliance with existing management guidelines that prohibit divers from chasing or harassing grey Nurse Sharks and blocking cave and gutter entrances is maintained.
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estimating the rate of quasi extinction of the australian grey Nurse Shark carcharias taurus population using deterministic age and stage classified models
Biological Conservation, 2004Co-Authors: Nicholas M Otway, Corey J A Bradshaw, Robert HarcourtAbstract:Abstract Grey Nurse Sharks off the east coast of Australia are listed nationally as “critically endangered” under Schedule 1 of the Environmental Protection and Biodiversity Conservation Act (1999) and may number no more than 300 in New South Wales and southern Queensland waters. They are an inshore, coastal dwelling species and were severely depleted by spearfishing in the 1960s. The population has continued to decline despite protection since 1984. Their life history (long-lived to 25+ years), late maturation (6–8 years), low fecundity (maximum 2 live young biennially), specific habitat requirements, limited inshore distribution, and small population size render them particularly vulnerable to extinction. We estimated the time to quasi-extinction (years elapsed for the population to consist of ⩽50 females) for the grey Nurse Shark population off the east coast of Australia based on current estimates of abundance and known anthropogenic rates of mortality. Estimated minimum population size was 300 as of 2002, and minimum anthropogenic mortality assessed from recovered carcasses was 12/year of which 75% were females. We modelled time to quasi-extinction using deterministic age- and stage-classified models for worst-, likely and best-case scenarios. Population size was estimated at 300 (worst), 1000 (likely) and 3000 (best). Anthropogenic mortality was added to the model assuming either all carcasses are being recovered (best), or conservatively, that only 50% are reported (realistic). Depending on model structure, if all carcasses are being reported, quasi-extinction times for worst-, likely and best-case scenarios range from 13 to 16 years, 84–98 years and 289–324 years, respectively. If under-reporting is occurring, time to quasi-extinction ranges from 6 to 8 years, 45–53 years and 173–200 years, respectively. In all scenarios modelled the grey Nurse Shark population will decline if no further steps are taken to remove anthropogenic sources of mortality. Because estimates of quasi-extinction rate depend on initial population size, and sensitivity analysis revealed that population rate of change was most sensitive to changes in the survival probability of the smallest length classes, obtaining precise estimates of abundance and annual survival of young females is critical.
