The Lifespan and Maximum Length of Grey Nurse Sharks
April 4, 2018 | Posted in: Sharks & Rays
According to the Facebook posting at https://www.facebook.com/FisheriesWA/photos/a.264218617326814.1073741827.246412385774104/486516945096979/?type=3&theater , a tagged 2.5 metre grey nurse shark, Carcharias taurus, caught by a recreational fisher in WA had been caught and released by Fisheries scientists 23 years earlier. Back in 1995, the shark was nearly 1.9 metres long and it was estimated to be four years old. This would mean that the shark was 27 years old at the time of its recent capture. The shark (sex unknown) had grown just 0.6m in 23 years, confirming a method that international shark scientists have been developing to determine the rate of growth of grey nurse sharks.
Grey Nurse Shark
(Taken by Steve & Noeleen Reynolds in 2005)
The shark had been first caught, tagged and released by Fisheries scientists east of Esperance on 11th November 1995. Its recapture by the recreational fisher, 365 kilometres from where it was last released, “is believed to be a world record for the longest time a tagged grey nurse shark has been ‘at liberty’ before being recaptured”. It has provided important information for managing the grey nurse shark population.
According to the web page found at http://www.fish.wa.gov.au/About-Us/News/Pages/World-record-tagged-shark-recapture.aspx , the “fisher caught the 2.5-metre shark on New Year’s Day at a remote location near Esperance and spotted the tag in the fish’s flank. All grey nurse sharks are totally protected from fishing in WA, and, having quickly taken the details from the tag, the fisher carefully released the shark and later (reported) the capture.”
According to “A Guide to Sharks & Rays” by Leighton Taylor et al, grey nurse sharks are also known as sand tiger sharks, spotted ragged-tooth sharks, or by the American spelling of gray nurse sharks.
The guide also suggests that they reach a maximum length of 3.2m. A 27-year old, 2.5m-long shark may still be some years short of its achievable length and life expectancy. In my article Grey Nurse Sharks (Carcharias taurus), I stated, “Their lifespan is unknown but thought to be somewhere between 16 & 25 years”. It now seems from the above that their lifespan is much more than 25 years.
According to Wikipedia, “Growth – In the north Atlantic, sand tiger sharks are born about 1 m in length. During the first year, they grow about 27 cm to reach 1.3 m. After that, the growth rate decreases by about 2.5 cm each year until it stabilises at about 7 cm/y. Males reach sexual maturity at an age of five to seven years and approximately 1.9 m (6 ft) in length. Females reach maturity when approximately 2.2 m (7 ft) long at about seven to ten years of age. They are normally not expected to reach lengths much over 3 m.”
This suggests that the 1.9m-long shark caught in 1995, possibly as a 4-year old female, was a sexually-mature female at 2.5m in 2018. At 27 years old though, it would seem to have been sexually mature for up to say 70% of its life.
If the shark kept growing at the rate of about 7cm per year (and it could grow to a length of over 3m), that it may reach an age of around 37 years. That would be a big increase on 16-25 years.
(Taken by Steve & Noeleen Reynolds in 2005)
According to https://www.legislation.gov.au/Details/F2007B00197 , “A Grey Nurse Shark held in captivity at a Sydney aquarium lived for 13 years, and others have lived for over 16 years in captivity in South Africa (Govender et al. 1991). The average life span of this species in the wild is unknown, although it is likely that larger specimens in the wild may be much older than 13 or 16 years (Pollard et al. 1996).”
According to https://www.hsi.org.au/go/to/115/fact-sheets-grey-nurse-sharks.html#.WsXoz0xuKP8 , “Females grow to approximately 318 cm, maturing at around 220 cm. Males attain a size of approximately 257 cm., maturing at 190 cm.” and “The lifespan of the Grey Nurse Shark is unknown, however those in captivity live to between 13 and 16 years.”
According to https://www.ehp.qld.gov.au/wildlife/threatened-species/endangered/endangered-animals/grey_nurse_shark.html , “grey nurse sharks are thought to live for between 30 and 40 years, grow to about 3.2m in length and are relatively slow to mature.”
I wrote to DPI NSW asking, “I am seeking details regarding the known max size and age of grey nurse sharks from NSW. It has been suggested that the species may grow to a length of up to 4m, and that they may reach an age of more than 30 years. Can someone please advise me whether or not this is true?”
I soon received this reply back from them: –
“Hi Steve, Thanks for your email concerning grey nurse sharks in NSW. In answer to your questions for the wild population off eastern Australia: (1) grey nurse sharks (males and females) can grow to a maximum length of 3.2 metres (maximum length is measured with the tail in a depressed position [flexed downwards] during a necropsy in a laboratory); and (2) they (males and females) can reach an estimated maximum age of 38 – 40 years, although very few individuals reach this age (which is estimated by counting the number of growth rings in the vertebrae). These statistics are very similar to grey nurse sharks in the disjunct populations elsewhere in the world where they are referred to as sandtiger sharks (i.e. off the east coasts of the USA, and South America) and spotted ragged-tooth sharks (i.e. off the east coast of South Africa). For example, the largest length recorded in a scientific publication for the sandtiger (grey nurse) shark of South America was 3.18 metres and a recent scientific publication estimated the maximum age off the east coast of the USA to be 35 – 40 years.
I hope this information is helpful. Regards, Dr Nick Otway | Senior Research Scientist | Marine Ecosystems”
I told Dr Otway, “Many sources still state ages of less than 20 years. That 2.5m-long tagged shark recently recaptured was said to be 27 years old. It could still live another 10 years and grow another 0.5m or so in the process.”
Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society's extensive back catalogue of newsletters and journals.