Marine Mammal Necropsy: an introductory guide for stranding responders and field biologists.

Abstract

Necropsies are performed to get further insight into the cause of death: in the case of marine mammals this may establish the cause for stranding or other mortalities. The necropsy generates a series of gross observations that establishes a differential diagnosis. Subsequent investigations, such as histopathology, are then guided as the various potential diagnoses are eliminated until an etiology is established. Regardless of whether it is a common chronic disease, fisheries interaction, or an emerging zoonoses, by consistently conducting necropsies, trends in population health can be monitored. This guide is designed to establish a base level of proficiency in marine mammal necropsy techniques. It is written for stranding network members who do not have a formal pathobiological training and have limited knowledge of anatomy. Anatomical and pathological jargon has been kept to a minimum. This manual is divided into six sections: preliminary data, sample management, pinniped, small cetacean, large whale (at sea and on the beach), and multiple appendices (A-H). A wellillustrated, carefully written gross necropsy report is essential to an adequate diagnostic investigation. Gross reports with significant detail and description tend to engender useful histopathological findings. A sample blank gross necropsy report and guidelines in writing a report can be found in Appendices A & B. Overall, this guide aims to lead the enquiring mind through the necessary steps to produce such reports. While this manual focuses on process and interpretation, it is important to understand that the gross necropsy is primarily about making detailed, descriptive observations without bias as to possible etiology. The necropsy should establish a list of differential diagnoses and the sampling be directed by an attempt to discriminate between them. Throughout this manual there are images of both normal and abnormal tissues documented in cases of stranded marine mammals on Cape Cod, Massachusetts. These images serve to give the beginner an example of what normal and abnormal may look like. We do not encourage the prosector to utilize these photos as a way to identify a specific pathology. The most important part of a necropsy is to accurately describe what you see as you see it. If experience has allowed one to recognize specific conditions, this information may be added to the report following the initial gross description. Note: To avoid confusion regarding the asymmetry of marine mammals, photos have not been arranged in the conventional manner with the cranial aspect to the left. Images are inserted into this manual as they were originally taken. Also, many of the images have been cropped for clarity, at times hiding the sample identification tag that should be included in every image. A gross description and morphologic diagnosis and/or etiology are provided with the majority of gross images throughout this manual. The morphologic diagnosis reflects subsequent histological 13 observations where available which are designated with an asterisk. Where histology is not available for a particular gross lesion image, similar prior cases with histological analysis have been used to infer a morphologic diagnosis. In addition, many gross appearances and common pathologies are similar among marine mammal species and photos throughout this manual can be applied to all orders discussed. This manual, although targeted for a US audience, has utility for any region of the world.