To whom it may concern: A new article has been published in the MARINE MAMMAL SCIENCE, 25(4): 902–919 (October 2009). Comparison of two histological techniques for age determination in small cetaceans P.L. Luque, J.A. Learmonth, M.B. Santos, E. Ieno, G.J. Pierce If you wish a copy, please feel free to write me (p.lastra@abdn.ac.uk<mailto:p.lastra@abdn.ac.uk>) for a pdf. ABSTRACT Age estimation in odontocetes is based on counts of growth layer groups (GLGs) deposited in recording structures such as teeth. Generally, tooth sections are obtained using a cryostat microtome. However, some researchers prefer obtaining thin sections using a traditional paraffin microtome. Little information is available on the application of this technique to dolphin teeth. Our main aim was to investigate if the paraffin technique can be a viable alternative. We considered whether estimated age would be affected by preparation technique, staining method, and section thickness, while controlling for effects of species, body length, and sex. We also analyzed whether the staining method would affect readability of GLGs and age reading variability. Teeth from 86 individuals (representing seven species) were used, but not all were prepared using both techniques because sufficient teeth were not available in all cases. Although the staining method had significant effects on the estimated age using both techniques, the variability of GLG counts was small and appeared to be similar for both techniques. Using Mayer’s hematoxylin stained sections of 8 _m thickness, good agreement of ages was obtained from both techniques, with more preparations classified as “good quality” for the paraffin technique. Mayer’s hematoxylin provided the best contrast of the GLGs when using the paraffin technique.We conclude that the paraffin technique is viable and represents a cost-effective alternative to a cryostat microtome when preparing cetacean teeth for age determination. Key words: age determination, small odontocete species, histological techniques. ------------------------------------------------------------------------------------------------------------------------------------------------------------ Dr. Patricia Lastra Luque University of Aberdeen, Tillydrone Avenue S/N AB24 2TZ EMAIL: p.lastra@abdn.ac.uk<mailto:p.lastra@abdn.ac.uk> Tlf:+(34)615617119 Centro Oceanografico de Santander Promontorio de San Martin s/n 39004 email: patricia.lastra@st.ieo.es<mailto:patricia.lastra@st.ieo.es> Tlf:(+34) 942291717/ 615617119 The University of Aberdeen is a charity registered in Scotland, No SC013683. The University of Aberdeen is a charity registered in Scotland, No SC013683.