My co-authors and I are pleased to announce a new paper recently published in Marine Mammal Science:  Accuracy and precision of age determination using growth layer groups for California sea lions (Zalophus californianus) with known ages. LAUREN B. RUST ,1 The Marine Mammal Center, 2000 Bunker Road, Sausalito,California 94965, U.S.A.; KERRI DANIL, Southwest Fisheries Science Center,NMFS, NOAA, 8901 La Jolla Shores Drive, La Jolla, California 92037, U.S.A.;SHARON R. MELIN, Alaska Fisheries Science Center, NMFS, NOAA, 7600 SandPoint Way N.E., Building 4, Seattle, Washington 98115, U.S.A.; BRENT WILKERSON,Department of Biological Sciences, University of Washington, Seattle, Washington98195, U.S.A. MARINE MAMMAL SCIENCE, 35(4): 1355–1368 (2019)© 2019 Society for Marine MammalogyDOI: 10.1111/mms.12605https://onlinelibrary.wiley.com/doi/abs/10.1111/mms.12605 AbstractAge determination from counts of growthlayer groups (GLGs) in tooth dentine is a common method for aging marinemammals. Using known-aged animals, we validated this method for acid etchedteeth of California sea lions (CSLs), Zalophuscalifornianus. Between 1991 and 2013, the upper left canine (n=33) was collected opportunisticallyduring necropsy from animals tagged or branded as pups that later died.Overall, 55%-61% of age estimates by GLG counting were within 1 yr of the known-agein the sample of 1-30 yr old CSLs. Accuracy of age estimates was found to bedependent on age of the CSLs, however. 71%-79% of age estimates were within 1 yrof the known-age in CSLs less than 10 yr old.  These findings support the validity ofcounting GLGs to estimate age for CSLs less than 10 yr old to within one yearof accuracy. For copies of the full PDF, please email: laurenbeddiarust@gmail.comThank you,Lauren Rust