Determining the Age of the Determining the Age of the Raja Raja radiataradiata

Garmen. Citation [internet]. Thorny Skate. Raja radiata Donovan 1808.1953.http:/www.gma.org/fogm/Raja_radiata.htm

Method 1 – Vertebral band countsMethod 1 – Vertebral band counts

Sampling specimens:Sampling specimens:• Specimens are caught in otter trawls in a 900 mile area.Specimens are caught in otter trawls in a 900 mile area.• Samples are taken in April, May & June.Samples are taken in April, May & June.

Preparation of vertebral samples:Preparation of vertebral samples:• Vertebral samples are taken above the abdominal cavity.Vertebral samples are taken above the abdominal cavity.• Three centra are taken from each specimen.Three centra are taken from each specimen.• Large centra cut sagittally.Large centra cut sagittally.• Small centra sanded down.Small centra sanded down.• Each vertebra mounted on glass microscope slides.Each vertebra mounted on glass microscope slides.• Vertebral sections digitally photographed.Vertebral sections digitally photographed.• Growth ring or band count is defined from the photograph.Growth ring or band count is defined from the photograph.

Determining resultsDetermining results

• The first distinct mark is known as age zero.The first distinct mark is known as age zero.

• Vertebra are analyzed by using MIA.Vertebra are analyzed by using MIA.

• With the estimated growth data Von Bertalanffy growth function is With the estimated growth data Von Bertalanffy growth function is fitted and then calculated by FISH PARM.fitted and then calculated by FISH PARM.

• 2.8% Coefficient of variation.2.8% Coefficient of variation.

• In older specimens the band pair formation are compressed.In older specimens the band pair formation are compressed.

• Juveniles are Juveniles are ≤ 80cm in total length, 103cm in adult males and 105cm ≤ 80cm in total length, 103cm in adult males and 105cm in adult females.in adult females.

Garmen. Citation [internet]. Thorny Skate. Raja radiata Donovan 1808.1953.http:/www.gma.org/fogm/Raja_radiata.htm

Method 2 – Caudal thorn readingsMethod 2 – Caudal thorn readings

• Caudal thorns are considered to be a rapid ageing tool.Caudal thorns are considered to be a rapid ageing tool.

• As the As the Raja radiataRaja radiata ages, the caudal thorn grows. ages, the caudal thorn grows.

• Due to this, the age of the specimen can be determined by looking at Due to this, the age of the specimen can be determined by looking at the size of the caudal thorn.the size of the caudal thorn.

• This is the better method of the two because determining the age of an This is the better method of the two because determining the age of an individual by using this method does not harm the specimen in anyway individual by using this method does not harm the specimen in anyway and it is not as costly.and it is not as costly.

• There is minimal inter structure bias.There is minimal inter structure bias.

ReferencesReferences

• Garmen. Citation [internet]. Thorny Skate. Raja radiata Donovan Garmen. Citation [internet]. Thorny Skate. Raja radiata Donovan 1808.1953.http:/www.gma.org/fogm/Raja_radiata.htm1808.1953.http:/www.gma.org/fogm/Raja_radiata.htm

• Walker.p.a, Heessen. H. J. L. 1996.ICES Journal of Marine Science, 53:1085-Walker.p.a, Heessen. H. J. L. 1996.ICES Journal of Marine Science, 53:1085-1093.1093.

• Avis J. C. 2000. Phylogeography: The history and formationof species, 1st Avis J. C. 2000. Phylogeography: The history and formationof species, 1st edn. Harrard University Press, Cambrdge.edn. Harrard University Press, Cambrdge.

• Julian. S. Huxley.1953. Zoogeography of the Sea. Great Britain: William Julian. S. Huxley.1953. Zoogeography of the Sea. Great Britain: William Clowes and Sons. 307-308pClowes and Sons. 307-308p

• Briggs, John. C. 1974. Marine Zoogeography. Mcgraw-Hill series in Briggs, John. C. 1974. Marine Zoogeography. Mcgraw-Hill series in population biology. United States of America: Mcgraw- Hill.287-288ppopulation biology. United States of America: Mcgraw- Hill.287-288p

• Grogan. J, Suter. S. 2006. Life Sciences. 11th ed. Sanlamhof. All Copy Grogan. J, Suter. S. 2006. Life Sciences. 11th ed. Sanlamhof. All Copy Publishers.8, 42pPublishers.8, 42p

• EFSA. Citation [Internet]. Thorny Skate (Raja (Amblyraja) radiata EFSA. Citation [Internet]. Thorny Skate (Raja (Amblyraja) radiata Donovan.1808, [cited 2008 April 04):www.efsa.co.uk/record/skatesthorny.htmDonovan.1808, [cited 2008 April 04):www.efsa.co.uk/record/skatesthorny.htm

• Environmental Biology of fish (2006) volume 77, Springer Netherlands. pp 3-4Environmental Biology of fish (2006) volume 77, Springer Netherlands. pp 3-4• Marine and Freshwater research (2007) volume 58, pp41-53Marine and Freshwater research (2007) volume 58, pp41-53