I have been busy doing an online course through Duke University. I was doing an 8-week course entitled “Marine Megafauna: An Introduction to Marine Science and Conservation”. At least two other people that have been associated with our Society also did the same course with me. It should be all over by the time that you read this newsletter. I have enjoyed doing the course, learning the subjects and (hopefully) achieving a certificate.
It is fair to say that doing the course took up some of my time normally spent on activities such as this newsletter. I thought that I could offset some of the time lost by including one of my writing assignments for the course in this newsletter: –
The mackerel shark Carcharias taurus has been known by several scientific names, and is often still referred to by names that have long since been superseded. Although the shark has been described as occurring within my Australian State’s waters (South Australia), I have never seen one, or even heard of one being sighted or captured. The shark has been described as dangerous to man and was hunted and killed to the verge of extinction years ago. It is still threatened by fishing practices.
Carcharias taurus is a mackerel shark (Order Lamniformes). Common names for the species include Grey/Gray Nurse Shark, Sand Tiger Shark & Spotted Ragged-tooth shark. Other Lamniformes include Mackerel Sharks, Thresher Sharks & Basking Sharks. There are 7 families of Lamniformes in total. The name Grey nurse shark is used in both Australia and the United Kingdom. It is the second-most-used name for the shark. The Grey nurse shark belongs to the family Odontaspidae (sand tiger family), which comprises some 5 species.
Carcharias.taurus has an elongated tail with a long upper lobe, a short, flattened snout, two large dorsal fins of similar size and three rows of large teeth. The species grows to a length exceeding 3 meters. The coloration for adults of the species is described as being bronzy above, gradually becoming paler below. Juveniles are said to have reddish or brownish spots scattered on the tail and rear of the body. These spots tend to fade with age. This shark is found off of some of the coasts of Australia, Africa, America & South America (western &
eastern Atlantic Ocean, western Indian Ocean & western Pacific Ocean). It is found in shallow bays, sandy coastal waters, and rocky or tropical reefs from shallow waters down to a depth of some 200 meters. Aggregations of them are often found by divers around
rocky outcroppings in offshore waters. There are two populations of them in Australia, an east coast population and a west coast population. The east coast population lives along the coast of New South Wales and southern Queensland. The west coast population lives in the southwest coastal waters of Western Australia. Their numbers are thought to be in the low hundreds.
Their lifespan is unknown but thought to be somewhere between 16 & 25 years. They make long coastal migrations for reproductive purposes. Males of the species fertilise females internally, via one of a pair of appendages called claspers, during copulation. Claspers are
extensions of the male shark’s pelvic fins. The species is ovoviviparous, which means that they produce eggs that develop and hatch inside the body. Aas many as 16-23 eggs may form in the two uterine chambers of the female. As these eggs hatch in the female’s
uteruses, the strongest pup in each uterus will cannibalise its weaker siblings prior to being born. Male Grey nurse sharks reach sexual maturity at 4-6 years and females at 6-8 years.
Grey nurse sharks have numerous fine-pointed teeth. These are curved and very sharp, and designed for capturing prey. They are said to be nocturnal feeders, actively foraging at night in relatively shallow reef areas. Their diet includes fish, small sharks, stingrays, squid
and crustaceans such as lobsters and crabs. Fish eaten will include both large and small bony fish.
Whilst researching the above details, I discovered that Grey nurse sharks are able to achieve almost neutral buoyancy by swallowing surface air and holding it in their stomachs. The near-neutral buoyancy that they achieve enables them to hover motionless in the water. I have probably witnessed this for myself, having dived in an aquarium with several of them in 2005.
Grey nurse sharks are gentle and are not considered dangerous. They would only attack a human when provoked. There appears to have been no fatalities from Grey nurse shark attacks. Grey nurse sharks, with their large teeth, have a ferocious look about them. They were long considered man-eaters and were hunted to near extinction. They have since been given some protection via legislation and marine protected areas.
In December 2002, ten grey nurse shark critical habitat areas were declared in Australia’s New South Wales’ waters with associated regulations to control fishing and diving activities.
The species had been declared both vulnerable and endangered. Unfortunately, some fishing practices continue to cause injuries and even death to grey nurse sharks. They still need much more protection to ensure their survival.
Dr Peter (Scarey) Last has made major contributions to Indo-Pacific ichthyology particularly within the fields of systematics, biodiversity and biogeography. He is regarded as a world authority on the taxonomy of sharks. Peter plays an active role in the IUCN
Shark Specialist Group assessing the conservation status of Australasian sharks. He discovered the high levels of elasmobranch biodiversity in local endemic species in the Indo-Pacific region which has led to the increasing focus on the conservation of sharks and
rays. Peter has studied the elasmobranch faunas in India, Japan, Thailand, Philippines, Borneo, Indonesia and New Zealand. Indonesian and the Philippines. In these countries, sharks and rays are overfished and his work has led to the development of national plans of
action for shark management and conservation.
- For further reading on the subject, the FishBase website has a webpage (date unknown) for Grey Nurse sharks.
- Peter Last & John D Stevens published a 513-page CSIRO book titled “Sharks and Rays of Australia” in 1994.
- Dicken, M. L.; Booth, A. J.; Smale, M. J.; Cliff, G. published a paper in 2007 titled “Spatial and seasonal distribution patterns of juvenile and adult raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa”. (Marine and Freshwater Research 58: 127. doi:10.1071/MF06018).
(Although I’m not fond of American spellings, I used a few of them in the above article as it was written for American judges/adjudicators.)