Summary of Southern Sea Otter Mortality Investigations in 2014

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Summary of Southern Sea Otter Mortality
Investigations in 2014
Melissa Miller, Erin Dodd, Francesca Batac, Colleen Young, Michael Harris, and
Laird Henkel
California Department of Fish and Wildlife
Office of Spill Prevention and Response
Marine Wildlife Veterinary Care & Research Center
1451 Shaffer Road
Santa Cruz, California 95060
May 2015
California Department of Fish and Wildlife
Office of Spill Prevention and Response Technical Report 15-1

Summary of Southern Sea Otter Mortality Investigations in 2014
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SUMMARY
Three hundred forty-eight southern sea otter carcasses were examined by California
Department of Fish and Wildlife scientists during 2014. Forty-six of those animals will
have histopathology completed in addition to a gross necropsy, including eight wild
tagged study animals, one animal outside the subspecies' normal range, 20 fresh-dead
animals collected from throughout the sea otter range in California as "random-source"
cases for full postmortem examinations, and 17 animals that had histology samples
taken due to other special circumstances. The remaining 302 otters received basic
gross examinations. Of the 20 random-source cases, 55% (n=11) were confirmed or
suspected shark bite cases. This is an increase from 36% (n = 8) of random fresh cases
that were shark bitten during 2013. The primary cause of death for the remaining nine
random-source sea otters encompassed additional mortality categories, including
presumed boat-strike for one animal. Microscopic examination (histopathology) and
supplemental testing are required to diagnose some health conditions affecting sea
otters. Thorough microscopic examination will be performed for all random source sea
otters necropsied during 2014. Our understanding of factors contributing to sea otter
mortality continues to evolve through time as additional knowledge is gained, new
disease processes are identified, and more diagnostic tests become available.
INTRODUCTION/BACKGROUND
The California Department of Fish and Wildlife (CDFW) has been investigating causes
of mortality in southern sea otters (Enhydra lutris nereis) since 1968, initiated in
response to State Senate Concurrent Resolution 74. Investigating causes of sea otter
mortality is important for: 1) identifying factors limiting population recovery, 2) informing
best achievable care of captive sea otters, including animals recovered during oil spills,
3) tracking mortality trends and better characterizing disease processes and emerging
threats, and 4) assessing, and when possible, mitigating anthropogenic sources of
mortality. Although it is not a primary focus of the California Department of Fish and
Wildlife, investigations of sea otter mortality can also help identify emerging health risks
for humans living along the land-sea interface of California.
Investigations of sea otter mortality are currently conducted by the Department's Office
of Spill Prevention and Response, at the Marine Wildlife Veterinary Care & Research
Center (MWVCRC) in Santa Cruz, in collaboration with partners at the United States
Geological Survey (USGS), the Monterey Bay Aquarium (MBA), and occasionally The
Marine Mammal Center. These groups collectively respond to every report of a stranded
sea otter, which may be recovered dead or alive. Most stranding recoveries in California
involve collection and examination of dead otters (Pattison et al. 1997, Kreuder et al.
2003, Miller et al. 2013). Of the few that strand alive, most die soon after stranding or
are humanely euthanized. Sea otters that strand alive with treatable health conditions
undergo rehabilitation at MBA and may be released or maintained in captivity. The
extent of examination and sampling of cases has varied over the years, but from 2010
through 2012, every 3rd fresh-dead otter older than 1 year was examined by a
pathologist at the MWVCRC, and more abbreviated necropsies were performed on all
other cases. In 2013, the sampling protocol was reduced to every 4th fresh-dead otter
older than 1 year to be examined by a pathologist at the MWVCRC with histology
(histology was limited in 2013, but a full suite of histology samples was taken in 2014).

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In addition, all tagged wild study animals and other animals of interest receive full
detailed necropsies at the MWVCRC. All other cases received gross necropsies that
were completed by a sea otter biologist and/or veterinary pathologist, and in some
cases, samples for limited histopathology or diagnostic testing were collected,
depending on the nature of each case and collaborator requests. Thorough microscopic
examination will be performed for all random source sea otters necropsied during 2014.
METHODS
Stranding Response
During 2014, biologists from the CDFW, USGS, and MBA, and in rare cases other
colleagues, responded to 386 strandings of live and dead sea otters throughout
California. Sea otters were recovered primarily from San Mateo County southward
through Santa Barbara County (the current established southern sea otter range). Three
extralimital strandings (sea otters found outside the established range limits) were also
recovered and examined in 2014.
Of the 386 stranded sea otters recovered during 2014, 375 animals were found dead,
stranded alive and died later, or were euthanized. Eleven live-stranded animals were
successfully rehabilitated at the MBA. MWVCRC staff performed postmortem
examinations on 90% (n=348) of stranding cases during 2014. Basic gross examination
data for all stranded animals is archived by USGS. Additional information on all 2014
strandings (i.e., age, sex, and location) can be found in the California Sea Otter
Stranding Network annual report, provided by USGS at:
http://www.werc.usgs.gov/proiect.aspx?proiectID=232.
Detailed Postmortem Examinations
Detailed necropsies were performed by a veterinary pathologist and/or technical staff at
the MWVCRC on 46 sea otters (plus one fetus) during 2014. These included eight
tagged wild otters that had been observed extensively during field investigations, one
stranded animal that had been rehabilitated and released by MBA, 20 random-source
animals (every 4th fresh wild otter carcass), and 17 animals that had histology samples
taken due to an unusual/atypical presentation or other special circumstances.
Detailed necropsies performed at the MWVCRC generally included a thorough gross
necropsy, a standard suite of photographs, collection of major tissues for microscopic
examination (histology), collection of swabs for bacterial and/or fungal culture, sample
archiving for longer-term study and ongoing research, and collection of samples for
additional diagnostic tests (e.g., potential exposure to biotoxins such as domoic acid)
pending future funding. During 2014 samples for full histopathology were collected for
each random fresh case selected. Postmortem radiographs were performed for some
cases, as directed by the history, stranding location, and case presentation. Preliminary
results presented in this report may be revised following completion of additional tests.
In some cases, the cause of mortality is listed as "possible" (suspected, but further
testing required to confirm, where possible, or final confirmation not possible due to test
or sample limitations), or "presumptive" (based on sufficient indirect evidence).

Summary of Southern Sea Otter Mortality Investigations in 2014
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The majority of results discussed below are limited to the 20 random-source animals
receiving detailed necropsies during 2014. Necropsy results for tagged and special
request animals will be provided to the submitting entities. Findings for tagged study
animals will be summarized as part of final reports for applicable field studies.
RESULTS
Random-Source Necropsies
Because a systematic sampling scheme is used to select for random-source sea otters
for detailed necropsy (every 4th fresh animal), these necropsies provide a relatively
unbiased index of current causes of sea otter mortality. However, due to relatively small
sample size and age-specific sampling bias (current diagnostic efforts are focused on
subadult, adult and aged adult animals), the diverse range of factors that are affecting
the southern sea otter population during any given year may not be fully represented.
During 2014, fresh, random-source animals were unevenly distributed by county of
stranding (Table 1) with three strandings in Santa Cruz, eleven in Monterey, and six in
San Luis Obispo Counties. One or two fresh, random cases were submitted for
postmortem examination each month, except for March and September, when three
cases were submitted each month. A summary of preliminary causes of mortality based
on gross necropsy findings is provided in Table 2.
Table 1. Number of random-source source sea otter necropsies by month and county of
stranding.
Month
Santa Cruz
Monterey
San Luis Obispo
TOTAL
January
1
1
February
1
1
2
March
2
1
3
April
2
2
May
1
1
June
1
1
July
1
1
August
2
2
September
1
2
3
October
2
2
November
1
1
December
1
1
TOTAL
3
11
6
20

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More than a half (55%) of the random-source otters that received full necropsy
examinations died with suspected (8) or confirmed (3) shark bite. Shark bite trauma is
confirmed by the presence of shark teeth or characteristic parallel scratches found on
bones. Shark-bitten sea otters were recovered from Santa Cruz (3), Monterey (5), and
San Luis Obispo Counties (3), and more were male (10) than female (1). Shark bite
cases occurred in February, March, May, and August through November, with two
cases each month except in May, August, and November, when there was one random
fresh case each month. All of these shark bite cases are presumed to have resulted
from attacks by great white sharks (Carcharodon carcharias), based on observed
trauma (Figure 1). Death from shark bite can occur acutely due to trauma and blood
loss, or more chronically due to bacterial infection of the bite wounds.
In addition to shark trauma, there was one random fresh boat strike trauma case. The
boat strike case was recovered in Monterey Harbor near the inner harbor boat launch in
July 2014 (Figure 2).
Direct Anthropogenic Cases
Cases with a direct anthropogenic suspected cause of death included the boat strike
case mentioned above (an adult male) as well as one gunshot case identified during
gross necropsy of a moderately decomposed carcass (not part of the random-source
sampling). The gunshot case was an immature female that was found at Sunset State
Beach (Santa Cruz County) in September 2014.
Extralimital Cases
Carcasses collected outside the normal range of the subspecies (not included as
random-source animals) in 2014 included an adult male collected in August at the
Humboldt Bay South Spit (Humboldt County; >400 km north of the northern range
periphery for southern sea otters), an adult male collected in December at Rodeo Beach
(Marin County; approximately 75 km north of the northern range periphery), and an
adult female collected in March at Malibu (Los Angeles County; approximately 150 km
Table 2. Primary cause of death for 20 fresh-dead, random-source wild southern sea
otters examined at the CDFW MWVCRC during 2014 (based on gross necropsy findings).
Cause of Mortality (Type)
Number
Percent
Shark Bite (Death due to shark trauma or secondary bacterial infection)
11
55%
Cardiomyopathy (Heart failure)
2
10%
Acanthocephalan Peritonitis (Abdominal thorny-headed worm infection)
2
10%
Disseminated Intravascular Coagulation (Blood clotting problems-can be associated with infection)
1
5%
Dystocia (Difficulties during pup birth)
1
5%
End Lactation Syndrome (Death due to the high metabolic cost of reproduction in females)
1
5%
Domoic Acid Intoxication - Presumptive (Marine biotoxin poisoning)
1
5%
Boat Strike
1
5%
Total
20
100%

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southeast of the southern range periphery). All of these cases were in a state of
advanced decomposition, making determination of the cause of death difficult. For the
case from Humboldt County, genetic testing was completed by the Seattle Aquarium
(Dr. Shawn Larson), indicating that this animal was a northern sea otter (E. lutris
kenyoni). The normal range of this subspecies extends south to central Washington
(>600 km north of Humboldt Bay). The other two extralimital animals are presumed to
be southern sea otters.
DISCUSSION
Since 2009, shark-associated sea otter mortality has increased significantly, and shark
bite has continued to be the leading cause of death for southern sea otters during 2014.
Studies to determine why there has been an increase in shark bite mortality in recent
years are in progress.
It is important to note that acute lesions, including shark bite or boat strike, may mask
significant, underlying disease. Many of the otters that died from shark bite during 2014
had other significant, pre-existing health problems that could have eventually led to their
death, had the animals had not been killed by sharks. It should also be noted that
biotoxins are important contributors to cardiovascular disease in sea otters, and many
cases of cardiovascular disease in sea otters may result from chronic or recurrent
biotoxin exposure.
Consistent with past mortality surveys, infectious disease continues to be an important
cause of death for southern sea otters: 10% (n=2) of fresh, random-source otters with
full necropsies succumbed to acanthocephalan (thorny-headed worm) infection of the
abdomen or secondary bacterial infections as a primary cause of death. Additional
animals had bacterial infection, as a contributing cause of death. It is also important to
note that some key infectious causes of sea otter death, such as single-celled
protozoan parasites (e.g. Toxoplasma gondii and Sarcocystis neurona), can only be
visualized through microscopic examination of tissues. Additional animals with
infectious agents as primary or contributing causes of death may be identified during
subsequent detailed microscopic examination and testing.
Relatively few cases of direct anthropogenic cause of death were identified in 2014,
although as discussed in the 2013 report (Miller et al. 2013), other causes of sea otter
death (or morbidity), such as bacterial infection, protozoal encephalitis and domoic acid
exposure may be indirectly anthropogenic.
DISCLAIMER
Information in this report is preliminary and should not be cited without permission from
the CDFW. Microscopic examination and supplemental testing is required to diagnose
some health conditions affecting sea otters. Because testing is still being completed,
and because our understanding of factors contributing to sea otter mortality evolves
through time as greater knowledge is gained, categories may be revised for future
mortality summaries.

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ACKNOWLEDGMENTS
Investigations of sea otter mortality at the MWVCRC were funded by the CDFW Oil Spill
Prevention Administrative Fund and the California Sea Otter Fund (through donations
from California tax payers). We thank the many volunteers and staff who helped with
sea otter mortality investigations during 2014, particularly Jessica Kunz, Angie Reed,
Fernando Lopez, Ben Shaw, Molly Spitler, Katie Greenwald, Christen Bechert, Amy
Wells, Ron Brost and Jack Ames.
LITERATURE CITED
Kreuder C., M.A. Miller, D.A. Jessup, L.J. Lowenstine, M.D. Harris, J.A. Ames, T.E.
Carpenter, P.A. Conrad, and J.K. Mazet. 2003. Patterns of mortality in southern
sea otters (Enhydra lutris nereis) from 1998-2001. Journal of Wildlife Diseases
39: 495-509.
Miller, M.A., E. Dodd, F. Batac, C. Young, M.D. Harris, J. Kunz, E. Berberich, and L.
Henkel. 2013.
Summary of southern sea otter mortality investigations in 2012. California
Department of Fish and Wildlife, Office of Spill Prevention and Response
Technical Report 13-1. 7 pp.
Pattison, C.A., M.D. Harris, and F.E. Wendell. 1997. Sea Otter, Enhydra lutris,
Mortalities in California, 1968 through 1993. California Fish and Game, Marine
Resources Division Administrative Report 97-5.

Summary of Southern Sea Otter Mortality Investigations in 2014
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Figure 1. Right tibial (calf) bone from a sea otter. Shark attack was confirmed at gross
necropsy through visualization of fine, parallel scratches on the bone surface consistent
with contact with a serrated white shark tooth. A shark tooth fragment was recovered at
this site. Great white sharks (Carcharodon carcharias) are the only local large sharks
known to possess these fine serrations along both tooth edges.
Figure 2. Left tibia and fibula from a sea otter: Compound fracture of both bones is
consistent with high-energy trauma, such as boat strike.