External Cetacean Necropsy

As much of WHOI's guide for pinniped necropsy is similar to that of cetaceans, I will be reviewing the latter section with more haste so that I can focus on advanced topics. This will also give me a chance to contrast seal and whale necropsies.

The external exam begins just the same as the pinniped's, by examining the carcass' condition. Before beginning, it is important to remember that stranded cetaceans are outside of their natural habitat, and thus apparent pathologies may actually be produced by the juxtaposition of a heavy, marine mammal in a foreign and inhospitable environment. Lacerations, bruising, organ compression and fluid pooling are to be expected, especially on long-dead specimens. Fresh carcasses (code 2) will have been stranded for less than 24 hours, while code 3 bodies will exhibit bloating, skin sloughing and other signs similar to that of the seal. Code 4 and 5 range from a collapsed carcass to mummified remains. Body condition is assessed by examining the dorsal side of the cetacean. Epaxial muscle of a robust animal is convex and rounded, while a thin animal will have a slightly sunken in girth. Emaciated cetaceans will exhibit concaveness and may have indentation of the nape.

Sex determination in cetaceans is slightly harder to do than for pinnipeds, in my opinion. the ventral midline will show a genital slit between the umbilicus and anus for both males and females. Positioning is the difference. Females should generally have their slit within 10 cm from their anal opening, while males have a greate distance. Short mammary slits may be found on either side of the genital slit in females, but may also be found in some males, and thus is not the best physical marker. Genital probing (using your finger, not weird alien equipment) can also be used. If your finger angles forward, the vagina has been entered, and if backwards, it is the penile opening. The penis may also be felt in this manner. Species differences may complicate this, but if all else fails, internal examination will reveal the truth.

Removing the skin & blubber: The cetacean should be positioned left-side up (as opposed to a ventral-side up in pinnipeds). Using a scalpel, a longitudinal incision should be made posterior to the blowhole and going down the dorsal midline, ending at the tail. Cutting perpendicularly, make 25 cm panels down the rest of the animal, making sure to make one panel under the axilla. Reflect the blubber away and cut through the fascia, revealing the skeletal muscle. Bruising in the skeletal muscle usually has a gelatinous texture and appears as a deep red or purple. The large epaxial muscle that powers the stroking action of the cetacean is then removed, along with any excess muscle on the backbone and ribs.

Next entry will tackle all of the internal anatomy of the cetacean.