Southern Sea Otter Rehabilitation: Lessons and Impacts from the Monterey Bay Aquarium

Abstract

As biodiversity continues to decline across the globe, conservation of wildlife species and the ecosystems they inhabit is more important than ever. When species dwindle, ecosystems that depend on them are also impacted, often leading to a decrease in the life-giving services healthy ecosystems provide to humans, wildlife, and the global environment. Methods of wildlife conservation are complex and multi-faceted, ranging from education and advocacy to, research, restoration, and rehabilitation. Here, we review a conservation program focused on helping recover the federally listed threatened southern sea otter (Enhydra lutris nereis) population. We describe the development of unique rehabilitation methods and steps taken to advance the program’s conservation impact. Understanding this evolution can inform conservation efforts for other vulnerable species and their ecosystems.

Full text

Citation: Konrad, L.; Fujii, J.A.;
Hazan, S.; Johnson, A.B.; Mayer, K.A.;
Murray, M.J.; Nicholson, T.E.;
Staedler, M.M.; Young, C. Southern
Sea Otter Rehabilitation: Lessons and
Impacts from the Monterey Bay
Aquarium. J. Zool. Bot. Gard. 2022,3,
641–652. https://doi.org/10.3390/
jzbg3040047
Academic Editors: Ursula Bechert
and Debra C. Colodner
Received: 30 September 2022
Accepted: 17 November 2022
Published: 24 November 2022
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4.0/).
Review
Southern Sea Otter Rehabilitation: Lessons and Impacts from
the Monterey Bay Aquarium
Leilani Konrad 1, *, Jessica A. Fujii 1, Sandrine Hazan 1, Andrew B. Johnson 2, Karl A. Mayer 1,
Michael J. Murray 1, Teri E. Nicholson 1, Michelle M. Staedler 1and Colleen Young 3
1Monterey Bay Aquarium, 886 Cannery Row, Monterey, CA 93940, USA
2Defenders of Wildlife, P.O. Box 401, Folsom, CA 95763, USA
3Marine Wildlife Veterinary Care and Research Center, Office of Spill Prevention and Response,
California Department of Fish and Wildlife, Santa Cruz, CA 95060, USA
*Correspondence: lkonrad@mbayaq.org
Abstract:
As biodiversity continues to decline across the globe, conservation of wildlife species
and the ecosystems they inhabit is more important than ever. When species dwindle, ecosystems
that depend on them are also impacted, often leading to a decrease in the life-giving services
healthy ecosystems provide to humans, wildlife, and the global environment. Methods of wildlife
conservation are complex and multi-faceted, ranging from education and advocacy to, research,
restoration, and rehabilitation. Here, we review a conservation program focused on helping recover
the federally listed threatened southern sea otter (Enhydra lutris nereis) population. We describe the
development of unique rehabilitation methods and steps taken to advance the program’s conservation
impact. Understanding this evolution can inform conservation efforts for other vulnerable species
and their ecosystems.
Keywords: aquarium; collaboration; southern sea otter; surrogacy; wildlife rehabilitation
1. Introduction
Conserving wildlife and ecosystems is increasingly important as biodiversity continues
to decline across the planet. While the intrinsic value of wildlife is clear, key species are
also vital in maintaining functioning ecosystems. One potential method to help restore
diminished wildlife populations and their ecosystems is the rehabilitation and release of
orphaned, ill, or injured animals [
1
]. Despite its highly complex and contextual nature,
wildlife rehabilitation can serve as a conservation tool to support the recovery of threatened
populations [
1
,
2
]. Understanding how the Monterey Bay Aquarium’s Sea Otter Program
has evolved to enhance conservation outcomes can inform future restoration efforts for
other threatened species and their ecosystems.
1.1. Wildlife Rehabilitation
The treatment and care of injured, diseased, and displaced indigenous wildlife, and
their subsequent release as healthy animals to native habitats in the wild [
3
] is a broadly
used conservation strategy for marine and terrestrial species. Thousands of wildlife reha-
bilitation programs exist globally, and the practice continues to grow [
4
,
5
]. These programs
include facilities and dedicated personnel to care for ill or injured wildlife, strategies to gal-
vanize public interest in the welfare of local wildlife populations, opportunities to advance
species-specific husbandry and veterinary care and methods to identify threats to wildlife
populations [1].
While most of these rehabilitation programs have a common goal of supporting
wildlife, their focus extends from the rescue and release of individual animals [
6
,
7
] to
larger-scale reintroduction projects of threatened and endangered species [
8
,
9
]. This broad
range in program focus is often influenced by available resources and the rehabilitation
J. Zool. Bot. Gard. 2022,3, 641–652. https://doi.org/10.3390/jzbg3040047 https://www.mdpi.com/journal/jzbg

J. Zool. Bot. Gard. 2022,3642
requirements of target animals. Because of their species-specific expertise, life-support
systems and facilities, and financial resources, some zoos and aquariums are well suited
to engage in wildlife rehabilitation. However, to achieve broader conservation goals,
programs may need to establish partnerships to leverage external expertise and resources.
These partnerships ultimately share or offset heavy fiscal burdens, inform strategies that
minimize threats to individual animals or the wild population, and assist in identifying
population-level conservation impacts.
By establishing these partnerships, a growing number of rehabilitation programs
are demonstrating their effectiveness beyond individual animal welfare and measuring
benefits to wild populations through post-release monitoring. For example, the California
condor (Gymnogyps californianus) recovered from the brink of extinction through rescue,
rehabilitation, and novel captive breeding and reintroduction techniques developed among
zoos, non-profit organizations, and government agencies [
10
]. In Florida, the Manatee
Rescue, Rehabilitation, and Release Program (MRP) is comprised of zoos and aquariums,
agencies, academic institutions, and non-profit organizations. Through increased post-
release monitoring and strategic interventions by MRP, 92% of subadult and adult West
Indian manatees (Trichechus manatus) and a relatively high proportion of calves were
rescued and released over a twenty-six-year period and successfully acclimated to the
wild [
11
]. In the Hawaiian islands, approximately 30% of the endangered Hawaiian
monk seal (Neomanachus schauinsalndi) population in 2012 was alive as the direct result of
either opportunistic interventions or rescue and treatment by cooperating federal and state
agencies and nonprofit partners [
12
]. These partnerships are examples of how rehabilitation
programs can provide measurable benefits to wild populations.
1.2. The Southern Sea Otter
Following near-extirpation during the 18th and 19th century maritime fur trade,
the southern sea otter (Enhydra lutris nereis) population has grown to 3000 individuals
throughout central California [
13
]. Despite this increase, the current population only
inhabits 13% of its historical range from Oregon to central Baja, Mexico (Figure 1) [
14
].
Since 1977, the southern sea otter remains listed as “threatened” under the Endangered
Species Act (ESA), and the population’s status and recovery plan are managed by the
USFWS under the authority of the Marine Mammal Protection Act.
Sea otters are considered a keystone species, playing a significant role in restoring and
maintaining the resilience of seagrass and kelp forest ecosystems through cascading trophic
relationships with their invertebrate prey [
15
–
20
]. Because they reside at the interface
between land and nearshore coastal waters, sea otters are susceptible to a wide variety of
natural and anthropogenic threats, such as shark bites, parasites, toxins, and infectious
diseases that may lead to stranding [
21
,
22
]. During their first six months, sea otter pups
depend on their mothers to nurse and nourish them, and teach them survival skills, such as
foraging, grooming, socializing, and avoiding threats [
23
,
24
]. If a sea otter mother cannot
find enough food to meet the high energetic requirements of pup rearing [
23
] or becomes ill
or injured, she may abandon her pup prematurely [
25
,
26
], threatening its survival without
human intervention.
Determining trends in sea otter strandings (e.g., cause and demography) is critical to
identifying threats to wild populations. The California Department of Fish and Wildlife
(CDFW; formerly CA Department of Fish and Game) began responding to and system-
atically documenting southern sea otter strandings in 1968. Since then, a network of
collaborators including CDFW, United States Geological Survey (USGS), Monterey Bay
Aquarium (MBA), and the Marine Mammal Center (TMMC) have worked together to
collect and examine stranded sea otters. Most sea otter carcasses receive a necropsy by
CDFW pathologists who, if possible, determine a primary cause of death. Sea otters that
strand alive are generally collected by MBA, TMMC, or CDFW and evaluated at MBA or
TMMC. TMMC and MBA are the only permitted facilities that currently rehabilitate south-
ern sea otters in California. Therefore any sea otters who are candidates for rehabilitation

J. Zool. Bot. Gard. 2022,3643
are reared and cared for by TMMC and MBA until they are released back to the wild or
deemed non-releasable and transferred to a long-term care facility.
J. Zool. Bot. Gard. 2022, 3, FOR PEER REVIEW 3
Figure 1. The current and historical range extent for the southern sea otter subspecies and (inset)
location of Elkhorn Slough in relation to the Monterey Bay Aquarium.
Determining trends in sea otter strandings (e.g., cause and demography) is critical to
identifying threats to wild populations. The California Department of Fish and Wildlife
(CDFW; formerly CA Department of Fish and Game) began responding to and systemat-
ically documenting southern sea otter strandings in 1968. Since then, a network of collab-
orators including CDFW, United States Geological Survey (USGS), Monterey Bay Aquar-
ium (MBA), and the Marine Mammal Center (TMMC) have worked together to collect
and examine stranded sea otters. Most sea otter carcasses receive a necropsy by CDFW
pathologists who, if possible, determine a primary cause of death. Sea otters that strand
alive are generally collected by MBA, TMMC, or CDFW and evaluated at MBA or TMMC.
TMMC and MBA are the only permitted facilities that currently rehabilitate southern sea
otters in California. Therefore any sea otters who are candidates for rehabilitation are
reared and cared for by TMMC and MBA until they are released back to the wild or
deemed non-releasable and transferred to a long-term care facility.
For nearly four decades, the Monterey Bay Aquarium’s Sea Otter Program has res-
cued, treated, and released stranded southern sea otters [16]. Reviewing this program’s
evolution highlights how wildlife rehabilitation potentially can support not only species
recovery, but also ecosystem restoration more broadly and affirms how partnerships and
collaborations may be leveraged for success.
2. Materials and Methods
2.1. The Monterey Bay Aquarium
The Monterey Bay Aquarium’s mission is to inspire conservation of the ocean. Since
opening its doors in 1984, MBA has advanced conservation through a fleet of animal hus-
bandry, communications, education, exhibition, guest experience, marketing, policy, and
research programs aimed at restoring and protecting California’s ocean and coastal eco-
systems. MBA has accomplished some of this work through rehabilitation efforts that ad-
vance the conservation of three imperiled California wildlife populations: the green sea
Figure 1.
The current and historical range extent for the southern sea otter subspecies and (inset)
location of Elkhorn Slough in relation to the Monterey Bay Aquarium.
For nearly four decades, the Monterey Bay Aquarium’s Sea Otter Program has rescued,
treated, and released stranded southern sea otters [
16
]. Reviewing this program’s evolution
highlights how wildlife rehabilitation potentially can support not only species recovery, but
also ecosystem restoration more broadly and affirms how partnerships and collaborations
may be leveraged for success.
2. Materials and Methods
2.1. The Monterey Bay Aquarium
The Monterey Bay Aquarium’s mission is to inspire conservation of the ocean. Since
opening its doors in 1984, MBA has advanced conservation through a fleet of animal
husbandry, communications, education, exhibition, guest experience, marketing, policy,
and research programs aimed at restoring and protecting California’s ocean and coastal
ecosystems. MBA has accomplished some of this work through rehabilitation efforts
that advance the conservation of three imperiled California wildlife populations: the
green sea turtle (Chelonia mydas), the Western snowy plover (Charadrius nivosus nivosus),
and the southern sea otter. Although MBA engages in a variety of activities to support
its conservation goals, in this paper we focus on its contributions to southern sea otter
recovery through its Sea Otter Program.
2.2. Methods
The MBA Sea Otter Program (hereafter, ‘program’) consists of multiple components
including stranding response, rehabilitation, population monitoring, research, husbandry,
and veterinary care. To achieve the program’s overall goal of southern sea otter recovery
during the last 38 years, these activities have been conducted in collaboration with state
and federal agencies, other non-profits, and universities. Although all of the program’s
efforts are equally important, this review focuses on the history of sea otter rehabilitation at

J. Zool. Bot. Gard. 2022,3644
MBA with an emphasis on aspects that may inform other wildlife rehabilitation programs.
We do so by highlighting successes and failures at critical stages that were formative in
the program’s evolution (Figure 2), summarizing southern sea otter stranding data, and
providing several examples of how collaboration has informed advancement in scientific
research.
J. Zool. Bot. Gard. 2022, 3, FOR PEER REVIEW 4
turtle (Chelonia mydas), the Western snowy plover (Charadrius nivosus nivosus), and the
southern sea otter. Although MBA engages in a variety of activities to support its conser-
vation goals, in this paper we focus on its contributions to southern sea otter recovery
through its Sea Otter Program.
2.2. Methods
The MBA Sea Otter Program (hereafter, ‘program’) consists of multiple components
including stranding response, rehabilitation, population monitoring, research, hus-
bandry, and veterinary care. To achieve the program’s overall goal of southern sea otter
recovery during the last 38 years, these activities have been conducted in collaboration
with state and federal agencies, other non-profits, and universities. Although all of the
program’s efforts are equally important, this review focuses on the history of sea otter
rehabilitation at MBA with an emphasis on aspects that may inform other wildlife reha-
bilitation programs. We do so by highlighting successes and failures at critical stages that
were formative in the program’s evolution (Figure 2), summarizing southern sea otter
stranding data, and providing several examples of how collaboration has informed ad-
vancement in scientific research.
Figure 2. A timeline of key successes and failures through the history of MBA’s Sea Otter Program
rehabilitation efforts, marked by transitions in methods (i.e., hand-rearing, ocean swims, surrogacy).
3. Results
3.1. The Program’s Beginnings
MBA rescued its first sea otters, when four pups separately stranded along the central
California coast between February and April of 1984, half a year before the aquarium
opened to the public (Figure 2). Aquarium staff hand-reared these pups, and because of
this intensive care by humans, the USFWS deemed the pups non-releasable and author-
ized MBA to provide long-term care while exhibiting the otters. After acquiring these in-
itial animals, the program continued to rescue, care for, and when possible, release
stranded sea otters of all ages. While it was not the original plan to rehabilitate or exhibit
sea otters in this new aquarium, support for the local sea otter population and the public’s
desire to help stranded individuals was clear.
Figure 2.
A timeline of key successes and failures through the history of MBA’s Sea Otter Program
rehabilitation efforts, marked by transitions in methods (i.e., hand-rearing, ocean swims, surrogacy).
3. Results
3.1. The Program’s Beginnings
MBA rescued its first sea otters, when four pups separately stranded along the central
California coast between February and April of 1984, half a year before the aquarium
opened to the public (Figure 2). Aquarium staff hand-reared these pups, and because of
this intensive care by humans, the USFWS deemed the pups non-releasable and authorized
MBA to provide long-term care while exhibiting the otters. After acquiring these initial
animals, the program continued to rescue, care for, and when possible, release stranded
sea otters of all ages. While it was not the original plan to rehabilitate or exhibit sea otters
in this new aquarium, support for the local sea otter population and the public’s desire to
help stranded individuals was clear.
As the number of sea otters in need of rescue continued to increase (Figure 3), program
strategies had to evolve. Although animals of all age classes stranded, the majority of
rescued older sea otters were in very poor health condition and only 22% (n= 146) were
able to be rehabilitated from a wide variety of stranding causes (Table 1).
By contrast, pups stranded in relatively good health and responded well to treat-
ment. With limited options for long-term placement of orphaned pups at other zoos and
aquariums, and a wild population still well below recovery, program staff had to explore
strategies for rearing pups for release to the wild. At the time, sea otter rearing strategies
were unknown, but staff explored two different rear-for-release methods in 1987 (Figure 2).
One case involved hand-rearing a pup prior to release, and in the other, an attempt was
made to establish a bond between a pup and a resident non-releasable adult female sea
otter. Neither strategy was successful, and program staff decided to continue to provide
human care but hypothesized that exposing pups to their natural environment during
development could aid in achieving more successful release outcomes. To do so, staff
established strong bonds with individual animals and conducted frequent ocean enrich-

J. Zool. Bot. Gard. 2022,3645
ment swims, which allowed the pups to explore nearshore rocky reefs and subtidal kelp
forests in Monterey Bay. The intent of these swims was to encourage prey identification,
foraging, and socialization with other wild otters in preparation for release as juveniles.
Although ocean swims provided enrichment and allowed young animals to develop diving,
swimming, and foraging skills, the close connection with human caregivers prevented
many of the pups from establishing a natural wariness of people and reintegrating with the
wild population after release [25].
J. Zool. Bot. Gard. 2022, 3, FOR PEER REVIEW 5
As the number of sea otters in need of rescue continued to increase (Figure 3), pro-
gram strategies had to evolve. Although animals of all age classes stranded, the majority
of rescued older sea otters were in very poor health condition and only 22% (n = 146) were
able to be rehabilitated from a wide variety of stranding causes (Table 1).
Figure 3. The number of sea otters that strand alive has increased over time, with annual fluctuations
(R2 = 0.8153). Likewise, the number of strandings responded to by the program has also increased
over it’s history (R2 = 0.6408). From the start of the program, the caseload has increased from five
animals in 1984 to nineteen at the start of surrogacy methods in 2002. From 1988 to 2002, when the
program focused on hand-rearing and conducting enrichment ocean swims with sea otter pups,
staff managed a caseload total of 213 animals, averaging 15 sea otters a year.
Table 1. Stranding causes of adult, subadult, and juvenile sea otters rescued, rehabilitated, and re-
leased throughout the program’s history (n = 146, see also Nicholson et al. 2018).
Stranding Cause Description No. Cases
Pre-mature weaning
Signs of emaciation or stunt-
ing due to early weaning or
chronic malnutrition during
weaning
38
ELS/mating trauma
Significant abrading or loss
of nose-pad due to mating
trauma (28), emaciation re-
lated to late-lactation (3)
31
Anthropogenic Trauma
Laceration, punctures, and
fractures consistent with boat
strike (2), fisheries interac-
tions/line entanglement (6),
tar or oiling (2), nonspecific
anthropogenic trauma (5)
15
Neurological disease
Fine muscle tremors, sei-
zures, and/or loss of motor
function
14
Acanthocephalan peritonitis Presence of acanthocephalan
parasites 11
Figure 3.
The number of sea otters that strand alive has increased over time, with annual fluctuations
(R
2
= 0.8153). Likewise, the number of strandings responded to by the program has also increased
over it’s history (R
2
= 0.6408). From the start of the program, the caseload has increased from
five animals
in 1984 to nineteen at the start of surrogacy methods in 2002. From 1988 to 2002, when
the program focused on hand-rearing and conducting enrichment ocean swims with sea otter pups,
staff managed a caseload total of 213 animals, averaging 15 sea otters a year.
Table 1.
Stranding causes of adult, subadult, and juvenile sea otters rescued, rehabilitated, and
released throughout the program’s history (n= 146, see also Nicholson et al. 2018).
Stranding Cause Description No. Cases
Pre-mature weaning Signs of emaciation or stunting due to early weaning or chronic
malnutrition during weaning 38
ELS/mating trauma Significant abrading or loss of nose-pad due to mating trauma (28),
emaciation related to late-lactation (3) 31
Anthropogenic Trauma
Laceration, punctures, and fractures consistent with boat strike (2),
fisheries interactions/line entanglement (6), tar or oiling (2), nonspecific
anthropogenic trauma (5)
15
Neurological disease Fine muscle tremors, seizures, and/or loss of motor function 14
Acanthocephalan peritonitis Presence of acanthocephalan parasites 11
Shark bite Lacerations from attempted depredation 11
Geriatric Pathology related to old age and poor dentition 4
Other Storm stress (1), respiratory disease (2), reproductive complications (1) or
unknown (18) 22
Total 146

J. Zool. Bot. Gard. 2022,3646
To closely monitor outcomes in the wild, sea otters receive intraperitoneal radio
transmitter implants [
27
], and staff track them intensively over a two-week post-release
period. Overall, sea otters released to the wild survived at rates comparable to their
wild counterparts [
25
], except for young pups. By comparison, only 27% of individuals
stranding as pups successfully reacclimated to the wild, while most required recapture and
permanent placement in zoological facilities because of a failure to forage successfully or
maintain a wariness of people [25,28].
As program staff explored how to successfully return young otters to the wild, its
caseload of all ages continued to increase from six animals in 1984 to nineteen in 2002
(Figure 3). Despite the labor-intensive nature of veterinary treatment, care, and enrichment
swims, the program admitted 213 live-stranded sea otters during this period (1988–2002),
rehabilitating and releasing just under 50%. Through ongoing studies of the wild popula-
tion, post-release tracking, and accumulation of data quantifying survival and reproduction
rates of released individuals of all ages, program staff identified the need for a shift in
rehabilitation methods to increase successful outcomes of stranded pups. Additionally, this
decision process was aided by findings from a Blue Ribbon Panel [
29
] (a panel of subject
matter experts) in 2002, which provided a framework for caseload management and clear
integration of research and conservation priorities to best utilize limited resources.
3.2. Surrogacy
After an early failure while pairing a pup with an adult female sea otter, starting
in 2001 the program re-explored using non-releasable females as surrogate mothers to
rehabilitate dependent pups. This strategy was reimplemented to limit interactions with
humans and leverage the natural maternal instincts of adult females to provide species-
specific care to sea otter pups. Based on historical cases of sea otter adoption [
30
,
31
], staff
believed this method would allow pups to better integrate with the wild population and
avoid humans following release. The first successful introduction between an orphaned
pup and a wild female in long-term care at MBA occurred in 2001 (Figure 2). Since then,
the program has used surrogacy as a method to rear stranded pups for release.
Sea otter surrogacy involves five key stages; (1) stranding response, (2) stabilization,
(3) surrogate rearing, (4) release preparation, and (5) post-release monitoring [
32
]. During
stabilization, staff provide hands-on care while wearing disguises to minimize pup habitu-
ation with humans. At this stage, pups develop basic grooming, diving, and foraging skills
before introductions to a surrogate female sea otter at approximately 8–10 weeks of age [
16
].
Once introductions are successful, mother and pup remain together during dependency
with limited human intervention [16]. At around 6 months of age, the pup is weaned (i.e.,
permanently separated) from its surrogate, and veterinary staff administer several health
exams in preparation for release [
16
]. Along with a VHF radio transmitter, released otters
are instrumented with a unique color and placement combination of hind-flipper tags
for identification in the field [
32
,
33
]. To assess how individuals are adjusting to the wild,
post-release monitoring in collaboration with TMMC, CDFW, and USGS, details an otter ’s
daily location, distance traveled, foraging success, behavior, and body condition.
With the development of these protocols, the focus of the program’s pup-rearing
efforts shifted from human-facilitated enrichment in the natural environment to surrogate-
fostering of natural behaviors such as diving, grooming, foraging, and socializing. To
assess whether this new method would result in greater success for released individuals
compared with previous hand-rearing methods, the program conducted a trial study of five
surrogate-reared pups that stranded from 2001 to 2003 [
25
] and were subsequently released
into Elkhorn Slough. This release site is a seven-mile-long estuary located approximately
20 miles north of MBA along the center of the Monterey Bay coastline as shown in Figure 1.
During the study, surrogate-reared pups integrated well into the wild population,
foraged successfully, and maintained their wariness of people [
25
]. The overall survival
rate one-year post release was 71%, which was significantly higher than the rate of success
(27%) prior to surrogacy [
25
]. These findings supported the shift in the program’s approach

J. Zool. Bot. Gard. 2022,3647
to rearing stranded pups and demonstrated the importance of post-release monitoring
and the scientific method for informing program development. Over the course of the
program’s history, MBA has responded to 80% of all live stranded pups (Figure 4), and
in recent years, as the numbers of live stranded sea otters of all age classes has increased,
collaborators such as TMMC have been rehabilitating more mature animals, allowing MBA
to focus on increasing its capacity for rehabilitating pups.
J. Zool. Bot. Gard. 2022, 3, FOR PEER REVIEW 8
During the study, surrogate-reared pups integrated well into the wild population,
foraged successfully, and maintained their wariness of people [25]. The overall survival
rate one-year post release was 71%, which was significantly higher than the rate of success
(27%) prior to surrogacy [25]. These findings supported the shift in the program’s ap-
proach to rearing stranded pups and demonstrated the importance of post-release moni-
toring and the scientific method for informing program development. Over the course of
the program’s history, MBA has responded to 80% of all live stranded pups (Figure 4),
and in recent years, as the numbers of live stranded sea otters of all age classes has in-
creased, collaborators such as TMMC have been rehabilitating more mature animals, al-
lowing MBA to focus on increasing its capacity for rehabilitating pups.
Figure 4. Throughout the program’s history, live pup strandings have steadily increased (R2 =
0.3929), and MBA responded to approximately 80% of these events. 50% of orphaned pups received
extended care at the aquarium prior to release or transfer to a long-term care facility. From its im-
plementation in 2002, only 28% of qualified pups (aged <10 weeks at stranding) were surrogate-
reared. Criteria for aging pups at this young stage included size (total length), weight, tooth erup-
tion patterns, and presence of natal pelage. Based on these methods, pup aging error is estimated at
+/− 2 weeks.
3.3. Conservation Impact of Releasing Surrogate-Reared Sea Otters
Through rigorous data collection, a series of collaborative scientific research projects
documented the positive conservation impacts of this program on local populations and
ecosystems. By conducting long-term monitoring of released sea otters (n = 37) from 2002
to 2015 as well as annual monitoring of the population of sea otters in Elkhorn Slough,
researchers were able to model the effect of this rehabilitation program on population
growth [16]. In 2002, the population in Elkhorn Slough was approximately 20 individuals,
and by 2015 it had grown to nearly 150 [34]. Based on release numbers and demographics,
as well as observed and estimated survival and reproductive rates of rehabilitated and
wild sea otters, surrogate-reared animals and their offspring were estimated to account
for 55% of overall population growth in Elkhorn Slough [16]. Additionally, the release of
female sea otters to this area likely contributed to a shift in the population from an area
dominated by transient males, to a stable reproductive population. In much the same way
that the presence of sea otters helps maintain kelp forests, increasing numbers of sea otters
in Elkhorn Slough supported eelgrass (Zostera spp.) growth and recovery from eutrophic
conditions, aiding in ecosystem restoration for other species in this habitat [17].
Figure 4.
Throughout the program’s history, live pup strandings have steadily increased (R
2
= 0.3929),
and MBA responded to approximately 80% of these events. 50% of orphaned pups received extended
care at the aquarium prior to release or transfer to a long-term care facility. From its implementation
in 2002, only 28% of qualified pups (aged <10 weeks at stranding) were surrogate-reared. Criteria
for aging pups at this young stage included size (total length), weight, tooth eruption patterns, and
presence of natal pelage. Based on these methods, pup aging error is estimated at +/−2 weeks.
3.3. Conservation Impact of Releasing Surrogate-Reared Sea Otters
Through rigorous data collection, a series of collaborative scientific research projects
documented the positive conservation impacts of this program on local populations and
ecosystems. By conducting long-term monitoring of released sea otters (n = 37) from 2002
to 2015 as well as annual monitoring of the population of sea otters in Elkhorn Slough,
researchers were able to model the effect of this rehabilitation program on population
growth [
16
]. In 2002, the population in Elkhorn Slough was approximately 20 individuals,
and by 2015 it had grown to nearly 150 [
34
]. Based on release numbers and demographics,
as well as observed and estimated survival and reproductive rates of rehabilitated and
wild sea otters, surrogate-reared animals and their offspring were estimated to account
for 55% of overall population growth in Elkhorn Slough [
16
]. Additionally, the release of
female sea otters to this area likely contributed to a shift in the population from an area
dominated by transient males, to a stable reproductive population. In much the same way
that the presence of sea otters helps maintain kelp forests, increasing numbers of sea otters
in Elkhorn Slough supported eelgrass (Zostera spp.) growth and recovery from eutrophic
conditions, aiding in ecosystem restoration for other species in this habitat [
17
]. Specifically
researchers identified a trophic cascade involving sea otters, crabs, and sea slugs that
enhanced grazing of epiphytic algae from eelgrass blades, improving health and density
of seagrass meadows [
17
]. Compared to measurements prior to the recolonization of sea
otters, eelgrass extent increased 60% [
35
]. These outcomes have provided scientific support

J. Zool. Bot. Gard. 2022,3648
for surrogacy as a rehabilitation method and for releasing these rehabilitated individuals to
enhance population recovery and ecosystem restoration.
3.4. Collaborative Conservation Research
Beyond the direct population and ecosystem benefits of releasing sea otters, reha-
bilitation has also contributed to conservation efforts by informing research and devel-
opment of veterinary and animal welfare protocols. This includes clinical diagnosis and
treatment [36–39],
adaptation of methods from techniques and technologies of other aspects
of medicine to sea otters [
40
–
44
], expansion of the idiosyncrasies of pharmacology [
45
], and
development/maintenance of a robust archive of biological materials sampled from sea
otters over several decades [46–49].
Rehabilitation of sea otters at MBA has also inspired research to advance sea ot-
ter husbandry [
50
], oiled animal care [
39
,
51
], and knowledge of sea otter biology and
physiology [
23
,
41
,
52
–
55
]. Findings from these collaborative research projects may inform
wildlife managers about how best to anticipate, overcome, and prevent, risks to sea otters
throughout a range of scenarios within wild and long-term care settings.
Sea otters undergoing rehabilitation have participated in collaborative experimental
research that would be impossible to conduct in the wild. For example, during controlled
exposure within monitored pools, sea otters demonstrated their vulnerability to drowning
within commercial finfish and shellfish traps, which was a suspected population threat. This
result led to a successful policy change that required the modification of fishing equipment
with the addition of a rigid 5-inch ring to fyke openings, excluding most otters from
entering and likely reducing sea otter entrapment [
56
]. These research advancements have
either informed or directly aided sea otter conservation efforts and show how collaboration
can magnify the benefits of wildlife rehabilitation.
4. Conclusions
4.1. Key Takeaway
MBA’s Sea Otter Program exemplifies lessons learned and knowledge attained through
rigorous research, methodological adaptation, and collaboration. Understanding how these
factors have shaped the evolution of MBA’s program can be helpful to other rehabilitation
and conservation partnerships with similar goals [
28
]. The dissemination of information
among programs can aid in addressing challenges in wildlife rehabilitation. The resource-
intensive nature of wildlife rehabilitation is always a major obstacle, but collaboration
provides alternative solutions and extends resources to achieve program goals. For MBA
and other programs, increasing collaboration and partnerships continue to advance meth-
ods of rehabilitation, post-release monitoring, and analysis of impacts to wild populations,
informing and improving conservation efforts into the future.
4.2. The Future
The evolution of this program resulted from a need to address the increase in live sea
otter strandings, as well as the growing knowledge that rehabilitation methods should
be informed by a scientific approach focused on improving individual animal and pop-
ulation welfare, and carried out in partnership with other groups and organizations. As
the program continues to evolve, this knowledge and approach will be important when
addressing future challenges in sea otter conservation.
Since the study at Elkhorn Slough, MBA’s rehabilitation program and its partners have
continued to successfully release animals in estuaries and open coast kelp forests within the
southern sea otter’s current range. Long-term survival of and reproduction by released sea
otters have contributed to their species’ keystone role of promoting healthier seagrass and
kelp forest ecosystems [
17
,
18
,
20
]. These ecosystem benefits indicate that expanding releases
for surrogate-reared sea otters could have local population-level and ecosystem benefits in
other areas throughout the California coastline. Continued post-release monitoring of wild

J. Zool. Bot. Gard. 2022,3649
sea otters is essential to understand how releasing otters within historical areas could aid
population recovery and nearshore ecosystem restoration.
Although sea otter population abundance has increased along the central coast of
California, the range extent of the population has remained mostly unchanged for the
last decade (Figure 5). The growth of the existing wild population is limited by the lack
of range expansion likely caused by shark bite mortality at the northern and southern
peripheries [
13
]. Because range expansion may be critical for achieving population growth,
MBA and its partners must focus their rehabilitation and release efforts in areas where
population numbers are low to contribute to southern sea otter recovery.
J. Zool. Bot. Gard. 2022, 3, FOR PEER REVIEW 10
released sea otters have contributed to their species’ keystone role of promoting healthier
seagrass and kelp forest ecosystems [17,18,20]. These ecosystem benefits indicate that ex-
panding releases for surrogate-reared sea otters could have local population-level and
ecosystem benefits in other areas throughout the California coastline. Continued post-re-
lease monitoring of wild sea otters is essential to understand how releasing otters within
historical areas could aid population recovery and nearshore ecosystem restoration.
Although sea otter population abundance has increased along the central coast of
California, the range extent of the population has remained mostly unchanged for the last
decade (Figure 5). The growth of the existing wild population is limited by the lack of
range expansion likely caused by shark bite mortality at the northern and southern pe-
ripheries [13]. Because range expansion may be critical for achieving population growth,
MBA and its partners must focus their rehabilitation and release efforts in areas where
population numbers are low to contribute to southern sea otter recovery.
Figure 5. Southern sea otter population density; measured as otters per square kilometer across the
extent of the subspecies range from 1985–2019. MBA is located at 36°37′4.8″ latitude
[34]
.
Adult sea otters exhibit strong site fidelity [57], which creates challenges when at-
tempting to rehabilitate and release them outside of the current range. MBA’s method of
releasing surrogate-reared juveniles could be a useful approach in addressing the popu-
lation’s lack of range expansion. Because an estimated 42% of releasable live strandings
are young pups without an established home range, this age class presents an impactful
rehabilitation opportunity. Since the start of the surrogacy program in 2002, MBA has only
reared 28% of live stranded pups for release (Figure 4). Further partnerships with other
zoos and aquariums could increase the capacity for surrogate-rearing orphaned pups,
which may aid southern sea otter range expansion efforts. As the program continues to
develop, existing and emerging partnerships will be vital in understanding if surrogacy
could be applied to sea otter reintroduction efforts to advance sea otter recovery under
the ESA.
Author Contributions: Conceptualization, J.A.F., L.K. and T.E.N.; Methodology, J.A.F., L.K. and
C.Y.; Data Curation, L.K., T.E.N. and C.Y.; Writing—Original Draft Preparation, J.A.F., L.K. and
T.E.N.; Writing—Review & Editing, J.A.F., S.H., A.B.J., L.K., K.A.M., M.J.M., T.E.N., M.S. and C.Y.;
Visualization, L.K.; Supervision, J.A.F. and T.E.N. All authors have read and agreed to the published
version of the manuscript.
Funding: This research was supported by generous donor contributions to the Monterey Bay
Aquarium.
Figure 5.
Southern sea otter population density; measured as otters per square kilometer across the
extent of the subspecies range from 1985–2019. MBA is located at 36◦3704.8” latitude [34].
Adult sea otters exhibit strong site fidelity [
57
], which creates challenges when attempt-
ing to rehabilitate and release them outside of the current range. MBA’s method of releasing
surrogate-reared juveniles could be a useful approach in addressing the population’s lack
of range expansion. Because an estimated 42% of releasable live strandings are young
pups without an established home range, this age class presents an impactful rehabilitation
opportunity. Since the start of the surrogacy program in 2002, MBA has only reared 28%
of live stranded pups for release (Figure 4). Further partnerships with other zoos and
aquariums could increase the capacity for surrogate-rearing orphaned pups, which may aid
southern sea otter range expansion efforts. As the program continues to develop, existing
and emerging partnerships will be vital in understanding if surrogacy could be applied to
sea otter reintroduction efforts to advance sea otter recovery under the ESA.
Author Contributions:
Conceptualization, J.A.F., L.K. and T.E.N.; Methodology, J.A.F., L.K. and
C.Y.; Data Curation, L.K., T.E.N. and C.Y.; Writing—Original Draft Preparation, J.A.F., L.K. and
T.E.N.; Writing—Review & Editing, J.A.F., S.H., A.B.J., L.K., K.A.M., M.J.M., T.E.N., M.M.S. and C.Y.;
Visualization, L.K.; Supervision, J.A.F. and T.E.N. All authors have read and agreed to the published
version of the manuscript.
Funding:
This research was supported by generous donor contributions to the Monterey Bay Aquarium.
Institutional Review Board Statement:
This study operated under U.S. Fish & Wildlife Service
permits #MA032027-2 and LOA032027-2, and Monterey Bay Aquarium permits #MA186914 and
#032027. All animal handling was in accordance with the requirements of USDA Class R Research
Facility license # 93-R-0476.
Data Availability Statement: Not applicable.

J. Zool. Bot. Gard. 2022,3650
Acknowledgments:
Jack Ames, Greta Austin, Gena Bentall, Allie Bondi-Taylor, Sue Campbell, Dave
Casper, Jennifer Coffey, Chris DeAngelo, James Estes, Katie Finch, Krista Hanni, Mike Harris, Katie
Hawkins, Julie Hymer, Michele Jefferies, Sonny Knaub, Erin Lenihan, Kaitlyn Reilly, Marianne
Riedman, Julie Stewart, Kattie Stong, Candace Tahara, Marcie Tarvid, Bob VanWagenen, Thomas
Williams, Linda Yingling, Marissa Young, and the many staff, volunteers, and interns past and present
at MBA and TMMC who helped care for, and track the many animals in the program.
Conflicts of Interest: The authors declare no conflict of interest.
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