Grey Nurse Shark Carcharias Taurus Research Articles

Population distribution, aggregation sites and seasonal occurrence of Australia’s western population of the grey nurse shark Carcharias taurus

Western Australia (WA) is host to a genetically discrete population of grey nurse sharks Carcharias taurus, listed by the IUCN as Near Threatened based on mean annual catch rates prior to protection within Australian waters in 1997. Only one small aggregation has been documented in WA to date with little data available on population dynamics, or spatial and temporal distribution along the WA coastline. We analysed C. taurus data from 16 years (2006-2021) of diver observations (2347 sightings) and commercial fisheries bycatch records (574 sharks), finding evidence of 4 new aggregation sites. Sightings at Shark Cave, a popular dive site near Perth, were related to water temperature and time of year (non-linear), with sightings per unit effort generally higher during the warmer months of summer and autumn (20-22°C). Evidence of fishing injuries was found on 17% of all C. taurus photo-tagged at Shark Cave. Strong site philopatry was apparent at most sites, and included a male shark that returned for 12 consecutive years to the Exmouth Navy Pier. This study confirms the range of Australia’s western population of C. taurus from near the South Australia/WA border, north to Shark Bay, with distribution extending further north along the coast when sea temperatures are lower (May-December). The beneficial role of citizen science in large observation studies such as this one is supported. However, while this research greatly increases the C. taurus knowledge base in WA, a large information deficit still exists. The identification and assessment of further aggregation sites is recommended, underpinning future management and protection measures for this iconic species.

Effective population size of the critically endangered east Australian grey nurse shark Carcharias taurus

Effective population size of the critically endangered east Australian grey nurse shark Carcharias taurus

Sustainability of threatened species displayed in public aquaria, with a case study of Australian sharks and rays

Zoos and public aquaria exhibit numerous threatened species globally, and in the modern context of these institutions as conservation hubs, it is crucial that displays are ecologically sustainable. Elasmobranchs (sharks and rays) are of particular conservation concern and a higher proportion of threatened species are exhibited than any other assessed vertebrate group. Many of these lack sustainable captive populations, so comprehensive assessments of sustainability may be needed to support the management of future harvests and safeguard wild populations. We propose an approach to identify species that require an assessment of sustainability. Species at risk of extinction in the wild were considered to be those assessed as threatened (CR, EN or VU) on the IUCN Red List of Threatened Species, or data deficient species that may be at an elevated risk of extinction due to life history traits and habitat associations. We defined sustainable captive populations as self-maintaining, or from a source population that can sustain harvest levels without risk of population declines below sustainable levels. The captive breeding and wild harvest records of at risk species displayed by Australian aquaria were examined as a case study. Two species, largetooth sawfish Pristis pristis and grey nurse shark Carcharias taurus, were found to have unsustainable captive populations and were identified as high priorities for comprehensive sustainability assessments. This review highlights the need for changes in permitting practices and zoo and aquarium record management systems to improve conservation outcomes for captive elasmobranchs.

The phylogenomic position of the grey nurse shark Carcharias taurus Rafinesque, 1810 (Lamniformes, Odontaspididae) inferred from the mitochondrial genome

The complete mitochondrial genome of the grey nurse shark Carcharias taurus is described from 25 963 828 sequences obtained using Illumina NGS technology. Total length of the mitogenome is 16 715 bp, consisting of 2 rRNAs, 13 protein-coding regions, 22 tRNA and 2 non-coding regions thus updating the previously published mitogenome for this species. The phylogenomic reconstruction inferred from the mitogenome of 15 species of Lamniform and Carcharhiniform sharks supports the inclusion of C. taurus in a clade with the Lamnidae and Cetorhinidae. This complete mitogenome contributes to ongoing investigation into the monophyly of the Family Odontaspididae.

Behaviour of aggregated grey nurse sharks Carcharias taurus off eastern Australia: similarities and differences among life-history stages and sites

Stereo-video photogrammetry was used to document swimming and non-swimming behaviours of various life-history stages of the grey nurse shark Carcharias taurus at 8 east Aus- tralian aggregation sites (during daylight) in the absence of scuba diving tourism and fishers. Swimming behaviours included hovering, milling, and active swimming with significantly greater milling. Rates of movement were least during milling and greatest for active swimming. Pectoral fins were held 20 to 24° below horizontal, which was consistent with holding positions reported in shark swimming studies. Significantly lower caudal fin positions during hovering probably minimised forward propulsion. Tail-beat frequency decreased significantly with increasing total length and was likely due to greater propulsion from larger caudal fins. Low activity indicated that sharks minimised energy expenditure when aggregated, which was associated with migratory and reproductive behaviours. Significantly different pectoral fin positions among sites likely resulted from differing navigational requirements. Non-swimming behaviours were infrequent. Chafing, gill puff, head snapping and palatoquadrate protrusion were generally categorised as grooming behaviour. One gill puff sequence and all but one rapid withdrawal event were cate- gorised as 'flight'-response agonistic behaviour. The remaining rapid withdrawal and stand back were to avoid collision and categorised as swimming behaviour. The absence of 'fight'-response agonistic behaviour was consistent with previous descriptions of the species as docile. This partial ethogram will enhance ecological understanding, assist assessment and management of diving tourism, and contribute to the recovery and long-term conservation of this critically endangered species.

First records of the grey nurse shark Carcharias taurus (Lamniformes: Odontaspididae) from oceanic coral reefs in the Timor Sea

The threatened grey nurse shark (Carcharias taurus) is reported for the first time from oceanic coral reefs in the Timor Sea. Generally known from temperate and subtropical coastal reef habitats, this species was encountered by Indonesian traditional fishers on oceanic coral reefs in an area of the Australian Exclusive Economic Zone known as the 1974 MoU Box, some 200 km from the Australian mainland. The presence ofC. tauruson these remote tropical reefs bears important management implications, including the species’ protected status in Australian waters and the challenges of regulating catches in areas permitted for traditional Indonesian fishing.

Hooked on fishing? Recreational angling interactions with the Critically Endangered grey nurse shark Carcharias taurus in eastern Australia

The grey nurse shark Carcharias taurus is critically endangered in eastern Australia. Although fully protected, instances of recreational hooking persist in this population, with potentially fatal consequences. Here we used in situ underwater video to quantify the rates at which C. taurus interacts with a range of proximately deployed recreational fishing gears, and we suggest appropriate management changes to limit such interactions. Bottom-set baits elicited strong responses, with 15 to 43% of whole and filleted mackerel baits depredated within 5 min. Smaller Australian sardine (pilchard) and squid baits were taken by C. taurus at a significantly lower, yet appreciable rate of 3 to 15%. These smaller baits were depredated more by recreationally important teleosts, although this relationship was not significant for sardine baits. There was no consistent diel influence on shark bait depredation, although C. taurus was the only nocturnal bait depredator. Trolled gears posed no direct threat to C. taurus at any time, even when trolled at depth. Benthic-oriented jigs were rarely snapped at by C. taurus, yet may still pose a foul-hooking risk as sharks showed a propensity to rub against these jigs at depth. Vertical jigs elicited little response by C. taurus, although foul-hooking was also a risk as jigs contacted sharks in 5% of proximate drops, with near misses or line-only interactions occurring in a further 6% of cases. Our findings suggest that restricting bottom-set baits and benthic-oriented gears such as jigs around C. taurus aggregations would be a feasible and enforceable strategy to minimise recreational fishing interactions.

Sharks of the Persian (Arabian) Gulf: a first annotated checklist (Chondrichthyes: Elasmobranchii)

The first evidence-based checklist of sharks of the Persian (Arabian) Gulf is presented based on appraisal of primary lit-erature and new data, including identifications verified by COI barcoding. Evidence of the occurrence of 26 species in theGulf is presented, and the possible presence of a further 17 species is discussed. Carcharhinidae is the most species-richfamily (16 species) present. The first substantiated Gulf records of the spinner shark Carcharhinus brevipinna, blacktipreef shark C. melanopterus¸ and scalloped hammerhead Sphyrna lewini are provided, along with a new record of the rarelyreported grey nurse shark Carcharias taurus. The diversity of the Gulf’s shark fauna, and possible influences on it, are briefly discussed.

Predator or scapegoat? The Australian Grey Nurse Shark through the public lens

The general lack of knowledge in mainstream Anglo-Australian society and popular Western media pertaining to the different shark species has led to the depletion of placid species such as the Grey Nurse Shark Carcharias taurus. This paper examines the depiction of sharks in Western popular media and also provides an in depth analysis of 155 Australian newspaper articles pertaining specifically to the Grey Nurse shark. The study of newspaper reportage consisted of a content analysis of 15 Australian based newspapers and serves to deconstruct the explicit messages that they attempt to convey to their readers. The data generated by this study exemplify the perceptions of C. taurus as represented by major Australian newspapers between the years 1969 and 2009. The study revealed that the majority of the news articles examined fell within a neutral range and that the level of interest in the plight of C. taurus has increased as C. taurus' circumstances have become more critical.

Recreational SCUBA diver interactions with the critically endangered Grey Nurse Shark Carcharias taurus

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 (= 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 non-invasive 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.

Reproductive periodicity, localised movements and behavioural segregation of pregnant Carcharias taurus at Wolf Rock, southeast Queensland, Australia

We examined grey nurse shark Carcharias taurus utilisation of Wolf Rock (which is located within a marine sanctuary zone and is the most northern known aggregation site on the east- ern Australian seaboard) between December 2002 and February 2008 using underwater censuses, photo-identification and acoustic tracking of individual sharks. Photo-identification surveys identi- fied 181 individual C. taurus (161 mature females, 1 immature female and 19 mature males). Eighty- one of these were re-identified at least once at Wolf Rock (77 females and 4 males) between Decem- ber 2002 and February 2008. A biennial reproductive cycle was indicated for 18 out of 28 females for which re-identifications spanned at least 2 mating and/or pregnancy events. Re-identifications of 9 out of 28 female sharks suggest that, on occasion, there may be 3 yr between pregnancy events. Male C. taurus were observed between July and January, but were absent between February and April. Fresh mating scars on female sharks were observed in late November and December and pregnan- cies were visible from late-February. Many pregnant sharks remained at Wolf Rock until August or September (9 to 10 mo post-mating) and demonstrated strong site attachment with 78 to 90% of their time spent within 500 m of the Wolf Rock aggregation site. C. taurus is listed as critically endangered along the east coast of Australia and there is concern about their population's resilience globally. The improved knowledge of the reproductive periodicity of C. taurus and their behaviour during preg- nancy will provide valuable information to assist with management throughout their distribution.

Correction for Peach and Marshall, The pit organs of elasmobranchs: a review

Correction for ‘The pit organs of elasmobranchs: a review’ by Meredith B. Peach and N. Justin Marshall (Phil. Trans. R. Soc. B 355 , 1131–1134. (doi: 10.1098/rstb.2000.0653 )). On page 1132, figure 2 depicts a pit organ from the grey nurse shark Carcharias taurus , not the epaulette shark Hemiscyllium ocellatum as stated in the figure caption. Page 1133, 3rd paragraph, 5th line, ‘(1 in = 0.025 m)’ was inserted incorrectly and should not be present.