What are Sea Otter Necropsies and Why are They Needed?


Timelapse sea otter necropsy (post-mortem examination) of adult female and pup conducted at California Department of Fish and Game.

Live Southern sea otters are never killed for the sole purpose of a necropsy (post-mortem examination).  The sea otters are either found dead or have been euthanized due to severe injury or disease that is considered unlikely to allow them to survive.  Some members of the public have asked us whether sea otters are killed for scientific research and we want them to know that the answer is definitely “NO”.  Southern sea otters are a California State fully protected species and a threatened species under the Federal Endangered Species Act.  All agencies working with live and/or dead Southern sea otters (e.g. California Department of Fish and Game (CDFG), Monterey Bay Aquarium and U.S. Geological Survey) abide by the necessary regulations put in place to protect the species.  Researchers are required to obtain a Federal permit to start any work involving sea otters and students work under one of the very few permitted researchers.  These permits help clearly define limitations to the research/study.

Today, the majority of all Southern sea otters found dead off the coast of California are brought to CDFG – Office of Spill Prevention and Response (OSPR) – Marine Wildlife Veterinary Care and Research Center (MWVCRC) in Santa Cruz for a necropsy or are conducted in the field by CDFG sea otter biologists.  Necropsies provide critical information on what kills sea otters as well as enhancing our knowledge of their anatomy, physiology, health and development, reproduction, and nutrition.  They allow us to determine a probable cause of death (COD).  Unlike skin lacerations or broken bones, most CODs are not visible externally.  Combining all the information from a case (field observations, any rehabilitation notes, and necropsy information) is necessary to complete the otter’s life story.  Also, the information acquired from these necropsies is kept in a searchable database for current and future use.  Our data has been used in various research projects and to watch trends in mortality.

Before the necropsy can begin, there is a checklist of things that need to be completed first.  Information gathered from this checklist can give insight on what to expect during the necropsy and we can prepare accordingly.  Examples of CODs that raise a red flag are zoonotic diseases (diseases transferable from animal to human) and bullets.  Extra personal protective equipment and safety measures are required for otters suspected to have a zoonotic disease.  Otters found with bullets or lead fragments will turn into a legal case in which evidence needs to be carefully collected and documented.

Depending on the location of carcass recovery or the possible circumstance surrounding the death, radiographs (x-rays) will be taken to check for abnormalities such as broken bones or bullet fragments.  Radiographs allow us to see the shape of the organs, find hidden broken bones and intestinal impactions without even opening the otter.   A standardized set of measurements and external photos are taken on all complete necropsies.  This consistency allows us to compare “normal” vs. “abnormal.”  Any wild or clinical information about the sea otter is evaluated beforehand and becomes part of the record.  This information can come from sea otter trackers, clinicians, rehabilitation centers or the general public.  After visually checking the outside of the otter for any irregularities and palpating (feeling through the skin) for lymph node size (to help determine the probability of a systemic or localized infection), the internal exam can start.

During the necropsy, all main organs and select lymph nodes are assessed and collected for histology (the microscopic study of stained tissues) and banked for future analysis.  Some forms of testing are funding-dependent so we will hold onto samples until a grant can be secured or if we work on a study with funding to run a particular test.  The veterinary pathologist and technicians are looking at size, shape, color and texture of all tissues and organs in comparison to the baseline of the normal for a healthy sea otter.  The state of decomposition might make the gross examination more difficult which is why complete necropsies are only conducted on freshly dead sea otters with a few exemptions.  Decomposed sea otters get an abbreviated necropsy that includes the examination of the internal organs but samples are not collected due to the tissues’ poor condition.  Comparing the otter to the baseline will guide the veterinary pathologist to a possible cause of death which will be later confirmed or refuted through cytology (the study of cells microscopically) and/or microbiology (the study of microorganisms).  Photo documenting the exterior and interior of the otter during the necropsy are important for writing the gross necropsy report and archiving.  These photos are used for scientific and teaching purposes as well.

Although it is sad for some to see sea otters on the necropsy table, they are helping their live counterparts tremendously.  And because they are such good sentinels of ocean health the information they provide helps protect people as well.  Knowing why or how sea otters are dying will help biologist learn more about each CODs, whether they are caused by or made worse by human activities and actions.  Biologists can use this information to educate the public and decision makers how to prevent these deaths.   With biologists and the public working together, we are hoping the Southern sea otter population can return to a sustainable level.

CDFG’s Jack Ames and Dr. Melissa Miller collecting morphometrics on a Southern Sea Otter at CDFG’s Marine Wildlife Veterinary Care and Research Center in Santa Cruz. (Photo: CDFG)

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Seaotters.com is an education and outreach initiative dedicated to raising awareness about California's threatened sea otters and the role research plays in the species recovery and conservation. It's a collaboration of the Monterey Bay Aquarium, U.C. Santa Cruz, U.C. Davis, U.S. Geological Survey, U.S. Fish & Wildlife Service, California Department of Fish and Wildlife, among others. We're #WildforOtters! Are you?