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GLG Case Study

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Determining age is extremely difficult when is comes to providing an accurate method that does not require the killing or substantial harm of animal. Most aging methods of marine animals involve counting of growth rings in hard structures, such as bone or teeth. For the Beluga and most Odontocetes scientists have been counting the growth layer groups (GLG) on their teeth. However, there have been conflicting reports on if Belugas lay growth bands annually or biannually. This is because scientists will use a variety of methods to confirm their hypothesis of 1 or 2 GLGs a year. Solving this discrepancy and finding an accurate method for aging is critical to the understanding of the Belugas life history. Knowing an animals life history allows …show more content…

If only one reader counts the GLGs they could be dramatically over or underestimating GLGs if there are multiple irregularities in the bands or if the reader isn't very good at counting them, whether its due to inexperience or they aren't detail oriented or they simply counted late at night. Consequently, the age would be inaccurate. In particularly studies that state that belugas deposit 1 GLG per year; each missed or double counted ring would be altering the age by a full year. Both papers used more than 1 reader, except Bella from Brodie's review, and take variance of counts into consideration using bias plots or CVs. The large difference in the methods used to determine if deposits happened 1 or 2 a year was the actual variability of the teeth themselves. More specifically Stewart's paper used archived wild teeth, while Brodie's review paper mainly touched on studies that used teeth from recently deceased captive animals. As mentioned many times throughout most papers, captive animals tend to have irregular deposit patterns in GLGs once they become captive. Who's then to say that the irregularities are not only in how the deposits form, but also in terms of how long they take to form. While we can only be certain that in captivity the deposits were 2 per year because we have the total amount of years in captivity; the age of

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