Sources of variation in counts of growth increments in vertebrae from gummy shark, Mustelus antarcticus, and school shark, Galeorhinus galeus : implications for age determination

• Published in: Canadian journal of fisheries and aquatic sciences 1996-08, Vol.53 (8), p.1765-1777
• Main Authors: OFFICER, R. A, GASON, A. S, WALKER, T. I, CLEMENT, J. G
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Galeorhinus galeus; General aspects. Techniques; Marine; Methods and techniques (sampling, tagging, trapping, modelling...); Mustelus antarcticus
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f96-103

Sources of variation in counts of vertebral growth increments from gummy shark, Mustelus antarcticus, and school shark, Galeorhinus galeus, were examined in vertebrae taken fronm the cervical, thoracic, and precaudal regions of the vertebral columns. Vertebrae from school shark were more difficult to read than those from gummy shark. The number of increments an experienced reader counted on the external surface of alizarin-stained whole vertebral centra was consistent with the number of major hypermineralized increments counted on microradiographs of vertebral sections. Differences between increment counts obtained by four different readers were significant. Increment counts by experienced readers were more precise and less biased between repeated readings. Increment counts from vertebrae sampled in the same region of the vertebral column were not significantly different. Increment counts from vertebrae sampled in different regions were significantly different and were highest for vertebrae from the thoracic region. Differences in increment counts between regions of the vertebral column may distort von Bertalanffy growth curves and therefore affect the reliability of fisheries stock assessments based on age-structured population models.