Radiography and Computed Tomography of the Mandible of a Stranded Offshore Killer Whale (Orcinus orca)
A mature adult female offshore killer whale (Orcinus orca) stranded deceased in Portage Bay, Alaska in October of 2015, and a full necropsy with histopathology was performed. The animal was first identified (O059) as an adult in the early 1990s, thus was at least 40 years old at time of death. As is consistent with previous reports of offshore killer whales, and thought to be a result of their unique elasmobranch diet, the teeth were significantly worn, all almost flush with the gingival margin on gross examination.1 There was pulp exposure in many of these teeth, along with tooth loss, and some remnant teeth were removed for aging and archiving. The portion of the mandible containing teeth (dentary bone) was sampled en bloc and frozen until imaging could be completed. Radiography and computed tomography (CT) were performed that revealed markedly widened alveoli with irregular margins. Severe lesions were located in the more mesial teeth. Comparing these images to those taken of a 3-year-old stranded killer whale of a different ecotype, and comparing to other species, these results suggest severe periodontal disease that may have affected the animal's ability to forage. Furthermore, gastrointestinal contents were scarce and this individual was in poor body condition. Gingival specimens were too autolyzed for meaningful histologic analysis. Overall, the postmortem examination confirmed emaciation and inanition as well as presumably age-related cardiovascular disease, the former of which was considered related to severe periodontal disease. This case highlights the importance of imaging in determining periodontal health and disease, especially post-mortem when other tissues are not available or are too autolyzed. Also, it raises the possibility that periodontal disease, potentially as a result of diet, may impact the health of free-ranging offshore killer whales.
The authors would like to thank Sadie Wright, Aleria Jensen, and Dr. Katie Savage of NOAA for their organization of the necropsy and sample disposition along with the Petersburg stranding network members Donald Holmes, Scott Roberge, Chris and Dr. Heidi Pearson, and Paul Nicklen for their assistance with the necropsy.
* Presenting author
+ Student presenter
1. Ford JKB, Ellis GM, Matkin CO, Wetklo MH, Barrett-Lennard LG, Withler RE. Shark predation and tooth wear in a population of northeastern Pacific killer whales. Aquat Biol. 2011;11:213–224.